SUMMER 2013 VOLUME XLIX - Fabled Jewelryucational organization for the gem and jewelry in - dustry. Postmaster: Return undeliverable copies of Gems & Gemology to GIA, The Robert Mouawad

VOLUME XLIX

Contrast Patterns for Optimizing Brilliance in Colored Gemstone Faceting

Fluorescence Produced by Common Optical Defects in Diamond

Quick Reference Chart for Optical Defects in Diamond

Nephrite Jade from the Italian Alps

SUMMER 2013

THEQUARTERLY JOURNAL OF THEGEMOLOGICAL INSTITUTE OF AMERICA

EDITORIAL63 Integrating G&G with GIA’s Gemology Education

Duncan Pay

FEATURE ARTICLES64 Optimizing Face-Up Appearance in Colored Gemstone Faceting

Al GilbertsonUnderstanding the human visual system of interpreting contrast patterns canreveal facet-planning techniques to increase perceived brightness and optimize agem’s appearance.

82 Fluorescence Produced by Optical Defects in Diamond: Measurement, Characterization, and ChallengesYun Luo and Christopher M. BreedingStudies of 3D fluorescence spectra from diamonds with different optical centersreveal that variations in UV lamp output can greatly affect observedfluorescence color and intensity.

98 Nephrite Jade from Val Malenco, Italy: Review and UpdateIlaria Adamo and Rosangela BocchioAnalysis of 21 rough and gem-quality samples offers an update on the composi-tion and properties of this pale green gem from the Italian Alps.

NOTES AND NEW TECHNIQUES107 Optical Defects in Diamond: A Quick Reference Chart

James E. Shigley and Christopher M. BreedingA simple chart on optical defects in diamond, including those that producecoloration and fluorescence colors.

REGULAR FEATURES112 Thank You, Donors

113 Lab NotesFreshwater cultured pearls with damaged nacre • Calcium fluoride coating found on 13 “Fancy” pinkdiamonds • Diamond with fish-like inclusion • Large irradiated green-yellow diamond • Strong colorzoning representing complex diamond growth environment • Very large single-crystal rough diamond • Unusual curved color zoning in emerald • Rare faceted neptunite

120 Gem News InternationalAncient tourmaline and beryl from Afghanistan • Orangy pink coated “soft coral” • Strands of tiny akoyakeshi pearls • Green kyanite • Banded mimetite • Turquoise-rock crystal composite • Imitation Larimar

Summer 2013VOLUME 49, No. 2

pg. 105

pg. 65

pg. 117

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About the Cover

The lead article in this issue examines the visual contrast patterns that optimize brightness in faceted gemstones.Brightness is superbly demonstrated by the gemstones shown on the cover, part of a collection of more than 100 tril-liant-cut stones on display at GIA Carlsbad. Clockwise from the top: 61.98 ct kunzite, 48.31 ct sphalerite, 9.67 ctgrossular garnet, 7.71 ct zircon, 12.27 ct sphalerite, and 29.59 ct spessartine. Center: 25.15 ct fluorite. Collection cour-tesy of Roz and Gene Meieran; photo by Robert Weldon.Printing is by Allen Press, Lawrence, Kansas.GIA World Headquarters The Robert Mouawad Campus 5345 Armada Drive Carlsbad, CA 92008 USA© 2013 Gemological Institute of America All rights reserved. ISSN 0016-626X

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Editor-in-ChiefDuncan [email protected]

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Ahmadjan AbduriyimTokyo, Japan

Shigeru AkamatsuTokyo, Japan

Edward W. BoehmChattanooga, Tennessee

James E. ButlerWashington, DC

Alan T. CollinsLondon, UK

John L. EmmettBrush Prairie, Washington

Emmanuel Fritsch Nantes, France

Jaroslav HyršlPrague, Czech Republic

A.J.A. (Bram) JansePerth, Australia

E. Alan JobbinsCaterham, UK

Mary L. JohnsonSan Diego, California

Anthony R. KampfLos Angeles, California

Robert E. KaneHelena, Montana

Lore KiefertLucerne, Switzerland

Thomas M. MosesNew York, New York

Mark NewtonCoventry, UK

George R. RossmanPasadena, California

Kenneth ScarrattBangkok, Thailand

James E. ShigleyCarlsbad, California

Christopher P. SmithNew York, New York

Wuyi WangNew York, New York

Christopher M. WelbournReading, UK

gia.edu/gems-gemology

EDITORIAL GEMS & GEMOLOGY SUMMER 2013 63

Duncan Pay | Editor-in-Chief | [email protected]

One of the things I’ve always wanted to do is create synergy betweenGIA’s gemology courses and Gems & Gemology. Many of the studentassignments incorporate research from the journal, and adding G&Garticles as references would provide support and validation for the infor-mation in our coursework.

As we added video media to our eLearning courses, we featuredinterviews with many of GIA’s research scientists, some of whom werealso G&G authors. Providing their articles to our students was a naturalnext step.

In the past, I had discussed this idea with Alice Keller when she was editor-in-chief of G&G.Although everyone was willing, we had no practical way to achieve it at the time. Now that everyissue is available free of charge on the redesigned GIA website at www.gia.edu, we can realize thisambition.

Beginning with our Diamonds & Diamond Grading eLearning course, we’ll provide links at theend of every assignment to specially chosen G&G feature articles.

Besides illuminating some of the source material for our coursework, links to supporting articleswill provide a truly meaningful pathway into the resources on our new website. Students withinquiring minds will find manyavenues of interest.

For example, I believe a good numberof students would choose to explorethe important G&G articles oncolored diamond, diamond treatment,or diamond synthesis. Others might also download articles focused on mining, production, andthe diamond supply chain, or read about the many famous gems examined or graded by GIA’slaboratory.

This tie-in exposes the tremendous amount of important work that G&G authors—bothinternal and external to GIA—have done to enrich our collective knowledge on the many aspectsof diamond, and makes it available to a wider, and younger, audience.

We’ll also provide a short student study guide that explains the structure of a typical featurearticle and explains how to navigate one.

In time, we’ll add similar links to relevant G&G articles in our other gemology courses.

Let me take this opportunity to thank all our current G&G print subscribers and online users. Ihope to welcome many more of you in the near future.

INTEGRATING G&G withGIA’s Gemology Education

Besides illuminating some of the source materialfor our coursework, links to supporting G&G arti-cles will provide a truly meaningful pathway intothe resources on our new website.

64 OPTIMIZING FACE-UP APPEARANCE IN GEMSTONE FACETING GEMS & GEMOLOGY SUMMER 2013

T here are many challenges in choosing a facetarrangement that optimizes a colored stone’sface-up appearance. What contributes to an at-

tractive appearance? In the field of cognitive science,experts have identified rules that govern our percep-tion of visual cues such as line, color, form, brightness,contrast, and motion. The subconscious processing ofthese cues is the work of each person’s “visual intelli-gence system,” wherein every aspect of our visual ex-perience is framed. In gemstones, brightness dependson how we process visual cues, so some patterns ap-pear brighter than others even when the measurablelight return is identical. Studying these rules can helpformulate design strategies to make gemstonesbrighter and more interesting. Tools exist for exploringthese aspects of appearance. Using these, cutters canchoose elements that will optimize the design. Effec-tive design requires an exploration of the best anglecombinations and placement of facets for a given ma-terial. Nevertheless, choices about appearance arepersonal. And while preferences vary, this study as-sumes the goal of improving scintillation while main-taining as much brightness as possible. Most coloredstone cutters understand their own preferences regard-ing visual contrast, depth of color, spread (shallow ordeep), brightness, and scintillation. By understandingcertain aspects of optimization, they can modify de-signs to suit their own preferences. Ultimately, this

will lead to a faceted gemstone with maximum appealgiven the constraints of the material at hand. Thispaper focuses on gems with colors that are not easilyweakened by pronounced brightness or darkness, sim-ilar to the medium range of tone and strong saturationfound in peridot (figure 1).

UNDERSTANDING BRIGHTNESS AND CONTRASTUnderstanding what creates the impression of bright-ness can help us map and plan areas in a gemstoneto enhance observed brightness.

Cognitive scientists understand much of the com-plexity of the stimuli processed by our visual system.For example, even though variations in lighting re-sult in varying wavelengths of light reflected from acolored surface, our visual intelligence system actu-ally works as a subconscious processor, assigning aconstant hue, saturation, and tone (which scientistsrefer to as “lightness”). This collaboration betweenthe visual system and the brain is constantly extract-ing information from a flood of sensations to con-struct a visual world. In the words of leadingcognitive scientist Donald Hoffman (1998), “You area creative genius. Your creative genius is so accom-plished that it appears, to you and others, as effort-less. Yet, it far outstrips the most valiant efforts oftoday’s fastest supercomputers. To invoke it, youneed only open your eyes.”

These scientists work primarily with two-di-mensional printed (opaque) images or flat images ona computer monitor, and they consider brightness asubjective attribute or property of an object being

OPTIMIZING FACE-UP APPEARANCE INCOLORED GEMSTONE FACETINGAl Gilbertson

FEATURE ARTICLES

The human visual system interprets visual cues to perceive different intensities of brightness. Patterns oflight and dark contrast create impressions of brightness in faceted gemstones. These patterns generallyremain coherent in the viewer’s eye when the gemstone is tilted or rotated. Using computer-generatedcolor-coded contrast maps in facet planning can improve apparent brightness, optimizing a gemstone’sappearance.

See end of article for About the Author and Acknowledgments.GEMS & GEMOLOGY, Vol. 49, No. 2, pp. 64–81,http://dx.doi.org/10.5741/GEMS.49.2.64© 2013 Gemological Institute of America

OPTIMIZING FACE-UP APPEARANCE IN GEMSTONE FACETING GEMS & GEMOLOGY SUMMER 2013 65

observed. Gemstones are three-dimensional andtransparent, and the light reflected from withinthem has a greater impact on their face-up appear-ance than the light reflected from the surface. Ourvisual intelligence processes visual cues so we seea gem that seems to generate light from within it-self, in a pattern that changes as the gem moves.This pattern is generated by the interaction of lightwith the faceting design.

Jose Sasián, a professor of optical sciences at theUniversity of Arizona, explains that while looking ata gem, the observer appears to see more facets than ac-tually exist. Sasián (2007) calls these “virtual” facets.These perceived facets are a result of different levelsof contrast, caused by light striking all the facets andthen splitting, creating the appearance of many morefacets.

How we interpret visual cues is critical to under-standing what creates a gemstone’s beauty, and bystudying these cues we can identify the elements toinclude in gem design.

The following is a general overview of the visualcues relevant to faceted, transparent gems.

Invisible Surfaces. Termed by some vision scientistsas “the invisible surface that glows,” the illustrationcreated by G. Kanizsa (1955) shows two different tri-angles that are more luminous (i.e., brighter) than thebackground, and whose borders are easily observedeven though there are no lines defining them (figure2). Using a photometer, one cannot detect any edgesof the triangle. The borders and luminosity are purelythe construction of the observer’s visual intelligencesystem. The brain uses a variety of cues to constructthese images, which we will refer to as “invisible sur-face maps.” In figure 3, the invisible surface map onthe left has a more luminous square area than themap on the right. How the brain perceives the linesthat resemble small “check marks” causes this dullereffect.

In the three “plus-symbol” outlines in figure 4, thefirst contains a square luminous area in the center. Inthe second image, the sides of the square bow inward

Figure 1. The conceptsdealing with bright-ness, scintillation, andoverall appearance arebest evaluated in a gemwhose color is not eas-ily weakened by mak-ing it bright or overlydark, such as peridot.Photo by Robert Wel-don, © GIA.

Figure 2. Observers see a bright, luminous triangle inthe center of both figures, even though there are nodefining lines. Cognitive scientists attribute this “in-visible surface map” to how our brain interprets visualcues provided by the contrast of light and dark. FromKanizsa (1955).

Figure 3. The visual contrast cues in this pair of invis-ible surface maps are different, causing our brain tointerpret the left square as brighter than the rightsquare. From Albert (1955).


due to the addition of visual cues (the four black dots).In the third image, the bowing disappears because thefour sets of lines have been shortened to square upwith the black dots. (Note: The brain can interpret vi-sual cues in more than one way. For example, somesee a circular rather than a square luminous area inthe leftmost image.)

Varying combinations of bright and dark cancause the observer to perceive different intensities ofbrightness. This does not address personal prefer-ences for different combinations. For example, theinvisible surface maps in figures 5A–5G demonstratevarious visual cues that create a bright circular areain the center. In each of these examples, the differentcues and their arrangements result in varying degreesof perceived brightness, leading to the impression of

an edge that is not really there—the invisible surface.Different types of pattern elements (such as bluntlines, dots, or wedges) can produce similar appear-ances, depending on how they are arranged. Elementsof varying brightness can also be embedded orstacked within each other (figures 5H–5J), creatingmultiple bright areas. Shifting the center of these em-bedded areas (figure 5I) does not disturb the impres-sions of brightness; the center has moved along withthe areas of contrast. Although these areas showstrong contrast, they are still coherent and bright,much like when a faceted gemstone is rocked. Theyare also present in non-round shapes such as the mar-quise or oval, as shown in figure 5J.

The ability to see these illusory bright areas in aninvisible surface map is enhanced by movement.When the image in figure 6 was “flickered” rapidlyon a computer monitor, the illusory center becamebrighter. When the flickering image was also rotated,the apparent brightness increased significantly. Theflashing of light and dark patterns caused by rotatingand flickering the image equates to the scintillationseen when we move a gemstone back and forth.Stronger contrast (black or gray areas against whitebackgrounds) also equates to stronger scintillation.Vision scientists have found that in certain cases animage stays organized or coherent in a viewer’s mindwhen the direction of observation is changed, asthrough movement.

Figure 4. These “plus-symbol” outlines have slightlydifferent visual cues. The first contains a squarebright middle area. In the second, the square appearsto have concave sides due to the four dots. With thethird, the bowing has been removed by shifting thefour sets of lines. From Petry (1987).

Figure 5. These invisible surface maps have slightly different contrast cues, resulting in the impression of bright orluminous circles (A–G). Contrast cues can also be stacked or embedded within each other (H–J) to give the impres-sion of multiple areas of brightness.

Brightness Contrast. Appraiser Michael Cowing,FGA, has published several articles on evaluating di-amond cut quality, coining the term “brilliance con-trast” to describe how contrast causes the brightnessobserved in diamonds (2009). Each of the circles infigure 7 is 50% dark and 50% light by surface area.A light meter confirms that each one is equallybright when printed on paper (even the gray ones).The checkered pattern of the bottom left circlemakes it perhaps the most visually interesting. If agem were able to return 100% of the light (all white),and no dark areas were visible, it would measure

brighter than a stone with dark areas of contrast—but its appearance would be far less appealing. For in-stance, the right column in figure 7 seems duller thanthe left due to weaker contrast. These images showthat while good light return is an important aspectof “brilliance,” contrast is a critical factor in face-upbrightness. Obviously, there comes a point when toomuch darkness or a poor distribution of darkness isless pleasing.

Figure 8 shows a common optical illusion knownas “White’s Illusion.” Although the rectangles in Bseem darker than those in A, they are actually ofequal luminance. In fact, they have the same graycolor. The gray areas embedded in dark stripes (A) ap-pear brighter than the gray areas embedded in whitestripes (B). This illustrates the concept of “lateral in-hibition,” in which the perceived brightness of anarea depends upon its surroundings (White, 1979).


In Brief• A gem’s brightness and attractiveness depends not only on how much light is returned but also on the contrast pattern or contrast distribution created by virtual facets.

• An idealized contrast plot shows the types of contrast distribution that contribute to effective gem designs to be used by faceters.

• Following rules for optimization, such as creating a design with the right contrast distribution, improves a gem’s appearance and increases its fire.

Figure 7. Each of these circles is 50% dark and 50%light by surface area. Yet the circles on the right aredull due to weak contrast. A gemstone’s visual interestdepends on good contrast. If it returned all light andhad no contrast, the gemstone would be uninteresting.

Figure 8. The rectangles on the right appear darkerthan those on the left, but they are actually the sameshade of gray. This demonstrates that the perceivedbrightness of an area depends on the surroundingsand the contrast. From White (1979).

Figure 6. Observers see a markedly increased bright-ness in the center circle when this invisible surfacemap is flickered on a computer monitor. When theimage is rotated and flickered simultaneously, thebrightness further increases. From Petry (1987).

In figure 9, the horizontal stripe and all six boxeshave the same brightness and color, but the squares’apparent brightness depends on the contrast of the sur-rounding area. In this illusion demonstrating “simul-taneous lightness contrast” (an example of lateralinhibition), apparent lightness is different from quan-titative lightness, the real measurement of the totallightness reflected from an object. The phenomenonalso occurs when a colored area is placed on a darkbackground, making it appear clearer, brighter, ormore luminous. In figure 10, for example, the navetteshapes at the bottom are identical, but they appear tobe different colors when placed on alternating lightand dark backgrounds (C). The difference is accentu-ated with the addition of an interwoven background(A and B).

Summary of Vision Science. Combining the ideas ofinvisible surfaces and brightness contrast, we can de-rive that darker contrast, placed in the right locations,can give faceted gems a brighter appearance. The areasof contrast need to be evenly distributed and notgrouped together; this is particularly true for areasunder the table. Our eye tends to gravitate toward thecenter to gather an overall impression of brightness.The diagrams in figure 11 illustrate how the place-ment of dark areas affects brightness. The patterns areidentical but contain varying levels of contrast. Theimage of highest contrast (bottom right, for most ob-servers) also has the brightest-looking center. This isa common goal in facet design, as dark centers, or“nail heads,” are undesirable in the jewelry trade.

From cognitive science we know that the appar-ent brightness of an invisible surface of definable

shape results from certain visual cues relating to dif-ferences of light and dark. The effect is further en-hanced by movement, and invisible surfaces can bestacked or embedded within each other. Strong con-trast makes a gemstone appear brighter and more ap-pealing, and the position of the contrast is also


Figure 10. The navette shapes throughout this imagehave the same tone but appear darker or lighter de-pending on the adjacent areas. From Sarcone andWaeber (undated).

Figure 9. The stripe and the small squares are all thesame shade of gray, again illustrating that perceivedbrightness relies upon its surroundings and the con-trast, which changes as the environment changes.From Purves (2011).

Figure 11. Varying the levels of contrast affects the ap-pearance of brightness. Each circle has the same pat-tern, but the areas of contrast vary in strength. Thecircle with the highest contrast (bottom right) has thebrightest-looking center.

A

B

C

important. Scintillation is more dynamic when thereis strong contrast between adjacent virtual facets.

If we understand what causes the cues for bright-ness in any shape, we can use this information to de-sign effective facet patterns by using strong contrastand ending the lines of contrast to produce a brightcenter. A gem’s brightness and attractiveness dependsnot only on how much light is returned—angles arestill important—but also on the contrast pattern cre-ated by virtual facets. Once an effective pattern is es-tablished, the major elements of that pattern mustremain in effect when the gem is tilted to maintainthe appearance of brightness. This means that thepavilion angles cannot be cut near an angle that allowsthe gem to “window,” letting light leak through. If theslightest tilt interrupts the pattern due to a window,the pattern is not effective because the contrast pat-tern has been eliminated. The impact of these effectsmay vary according to the level of brightness, as dic-tated by refractive index and color saturation.

TOOLS FOR ASSESSING CONTRASTIf contrast is an important part of faceting various gemmaterials, there needs to be a reliable method to de-termine elements of contrast. Most critical is the con-trast caused by the reflection of the observer’s headand torso. Harding (1975) first identified this criticalelement: the effect of an observer’s head blocking raysof overhead illumination. He calculated the rays re-turned from the gem to the viewer’s eyes, as well asthe illumination blocked by the viewer’s head.

Regarding head obstruction, Harding writes, “Forultimate liveliness it should be possible to see reflec-tions in the table from both sides of the pavilion withboth eyes at once. At a viewing distance of one foot,as shown in [figure 12], the angle between reflectionsto both eyes (two different rays) is about 12°. To seereflections from both sides with both eyes, therefore,the minimum external table reflection angle must beat least 6°.” While not directly discussing the needfor contrast, Harding alluded to its importance. Ofcourse, liveliness stems from scintillation, the resultof strong contrast between neighboring facets whenthe gem, the light source, or the observer moves.

This concept was also part of Kazumi Okuda’sgroundbreaking work in about 1980. His experimentswith reflectors—“hearts and arrows” viewers haveevolved from these devices—led to the FireScope™introduced by JDM in Japan. JDM used the black re-flection of the lens as a dark contrast against a red re-flecting field (figure 13). Studying the black reflection,they determined the importance of certain reflection

patterns in diamond appearance, as shown in an un-dated FireScope brochure, circa 1987.

It should be noted that an observer both blockslight from the rear and reflects light from the frontor side. In most environments, however, far less light


Figure 12. A gemstone’s liveliness is the result of scin-tillation: the strong contrast between neighboringfacets when the gem, the light source, or the observermoves. An observer’s head (shown from above) ob-structs overhead light, causing a sharp change in thelight streaming into the gem. Note that at a viewingdistance of one foot (approximately 30 cm), the anglebetween the two reflected rays that return to botheyes is about 12°. From Harding (1975, figure 8).

Figure 13. The FireScope by JDM uses the black reflec-tion of the viewing lens as a dark contrast against ared reflecting field. Studying the patterns of differentdiamonds, JDM concluded that the most attractivediamonds have a certain contrast pattern. From anundated FireScope brochure, circa 1987.


is reflected into the gem from the observer’s head andshoulders than from around and above the observer.The observer’s reflection therefore serves as themajor source of contrast in the lighting environment.

To better understand this, consider what a facetedgem might look like in a totally diffuse white-lit en-vironment (figure 14). If the gem reflected nothingbut white light, it would have no contrast (A). If youwere to cover your face and shoulders with a fluores-cent red mask and view the gem in the same envi-ronment, you would see red contrast (B). If youmoved closer to the gem, there would be even morered reflected throughout it (C).

In 1997, this author started experimenting withcolor coding of light (and contrast) entering a stonefrom various angles (“Reflector technologies,” un-dated). By constructing a hemisphere or dome withconcentric rings of color (figure 15) and viewing thestone through an aperture at the top of the dome, onecan see that the gem gathers its light from the col-ored rings. DiamCalc, a 3D modeling program intro-duced in Russia in March 1999, uses ray tracing toalter the proportions and angles of a diamond imageviewed on a computer monitor. By 2000, color-codedlighting environments were added, allowing themodification of angle of arc as well as color. Diam-Calc can model virtual polished gemstones in a vari-ety of realistic lighting environments, includingGemCad’s ISO and COS, Fire Scope™, Ideal-Scope,ASET (Angular Spectrum Evaluation Tool), and AG,

the author’s own environment. GemCad is a popularcomputer-aided design (CAD) program used to createaccurate 3D models of a faceted gemstone. DiamCalcaccepts GemCad and other designs and allowschanges in table size and girdle thickness, as well asfacet angles and azimuths, for a variety of standardshapes. DiamCalc can also create motion pictures ofa gem being rocked or otherwise moved from side toside in these lighting environments. The software iswidely used in the diamond cutting industry to planrough and design new cuts. It can accept files fromGemCad (.asc format), Sarin (.srn), Helium (.mmd),and Autodesk (.dxf or .stl), as well as certain .txt files.It can generate the following file formats: AutodeskDXF (.dxf), GemCad (.asc), and binary and ASCII STL(both in .stl format). For colored stone cutters, it al-lows variations in refractive index for modeling var-ious gem materials.

DiamCalc does not model double refraction, so theeffects of a closed or dark c-axis cannot be predicted.Many stones are dichroic, which means one sees dif-ferent colors in different directions through the gem.Some gems with this property will show nearly iden-tical colors in all directions, while some will show onlydifferences in color density (darker or lighter tone). Forexample, tourmaline often has extreme dichroism, andthis characteristic is referred to by many gem cuttersas a “closed c-axis” or “dark c-axis.” In other words,light does not pass through one axis (direction) of thestone, or only passes in a limited amount.

Figure 15. Gemstonesgather light from the sur-rounding viewing environ-ment. When placed undera hemisphere lined withconcentric rings of variouscolors (left and center), agemstone (right) returnsthe colors of the dome.

Figure 14. These photos showthe same gemstone under dif-ferent viewing conditions: (A)under totally diffused whitelight; (B) under the same en-vironment, with the observerwearing a red mask and gar-ment; and (C) with the ob-server standing closer. Fromthese, it is apparent that theobserver sees much of theirown reflection, as dark con-trast in the gemstone.

A B C


Comparison of Two Important Models. While Diam-Calc supports a variety of lighting environments,this paper deals with two of particular value in de-sign optimization: AG and ASET (figure 16). Theseare variations of the color coding of light entering adiamond from specific surrounding arcs, patented in2000 (Gilbertson, 2003) and 2004 (Caudill et al.2008), respectively. While either can be used as a pri-mary environment for planning or as a secondarydouble check, the AG environment offers certain ad-vantages as the primary. Comparing the three-colorASET and the five-color AG patterns for the samestone, observe how their angles of light orientationdiffer. Key information about both the observer(black, 83°–90°) and the lower angles of light entrylikely producing a strong contrast (dark violet,40°–55°) are not represented well in the ASET image.Three color-coded zones do not provide enough in-formation, as certain patterns with strong contrast(black) can produce some of the visual cues leadingto different preferences.

If a design is planned with AG and then checkedwith ASET, however, nuances and slight weaknessesin design can be captured and modified later. Theseexamples represent diamond’s RI and the sets of an-gles considered optimum for diamond appearance.Since individuals may prefer different patterns,

which can vary depending on RI, it is advisable to de-termine personal preference before analyzing pat-terns with AG and ASET lighting.

DiamCalc also allows the background to be color-coded. A black background is the default setting forboth the AG and ASET environments, but white isalso available. Areas where light passes through thegem from the background (“windows”), are indicatedas white in the contrast plot when using the whitebackground.

PRACTICAL APPLICATIONPast work can be useful for further understanding theAG lighting environment. For example, both GIAand the American Gem Society have determinedthat the most appealing round brilliant-cut diamondshave a balance of contrast and brightness (GIA, 2006;Sasián, 2007). The contrast maps of a typical well-cutdiamond are shown in figures 16 and 17 to illustratethe relative balance of the various color-coded lightentry angle ranges. Much like the invisible surfacemap examples in figure 5, these color-coded contrastmaps can explain the pattern seen in the cut gemwith AG lighting (figure 17).

With the AG environment, note that there is verylittle black (83º–90º). The black areas representing theretro-reflection of the observer should be minimized

Figure 16. Two of thelight color-coding mod-els supported by Diam-calc—AG andASET—can be used formapping contrast ingemstone designs. Dif-ferent aspects of con-trast in the samegemstone can be seenusing the three-colorASET environment andthe five-color AG envi-ronment.

ASET (+ white)Green = 0° (horizon) to 45°Red = 45° to 75°Blue = 75° to 90°

AG (+ white)Light Blue = 0° (horizon) to 40°Dark Violet = 40° to 55°Green = 55° to 70°Red = 70° to 83°Black = 83° to 90°

Blue75°-90°

Red45°-75°

Green0° (horizon) to 45°

Light Blue0° (horizon) to 40°

Violet40°-55°

Green55°-70°

Red70°-83°

Black83°-90°

None


or removed in planning colored stones. The lowest an-gles of light entry represented by violet (40º–55º) willappear darker, along with any areas of windowing,which produces a very nice balance of varying con-trasts within the gem. These examples are comparableto the dark areas in the invisible surface maps.

The contrast maps display a substantial amountof green, which is represented by light coming fromaround the observer’s head (55º–70º). The red (70º–83º) is arranged in a narrow, wagon-wheel patternfrom the girdle edge to the near-center. Red areas canappear dark or bright, depending on the observer’sproximity to the gem or how much it is tilted. Bothof these colors indicate the primary areas of bright-ness in a gem, comparable to the white area in theinvisible surface maps. An effective design requiresthese areas of brightness to be prominent and welldistributed, with the dark areas creating a balanced,contrasting pattern in the gem.

Contrast maps are similar to a much more com-plex stacked invisible surface set (such as figure 5H–J). As the invisible surface maps are moved androtated, the apparent brightness increases dramaticallyand remains organized in a viewer’s mind even whenthe direction of observation is changed. This meansthat movement (rotating and flickering) of the invisi-ble surface maps is comparable to the scintillationseen when a gemstone moves back and forth. Withthe proper types of contrast in adjacent virtual facetsof the red areas, the gem will be more interesting andattractive, and in many cases appear brighter. Notethat while brightness may be the goal, too many areasof brightness can lighten the saturation of the color inlarge portions of the gem, lowering its market value.

EXAMPLESFigure 18 shows examples of various gems purchasedfrom the trade for GIA’s Dr. Eduard J. Gübelin Col-lection. The individual gems were scanned using anon-contact measuring device to derive the facet an-gles and arrangement. A photo of each gem, showingthe representative pattern viewed face-up, is accom-panied by an AG contrast map derived from Diam-Calc. The observer’s face and torso are about 18–20inches from the stone, and the photo captures a goodrepresentation of what the observer would typicallysee in the gem. The following is a brief discussion onthe appearance of each gem.

Figure 18A: This native-cut golden sapphire (RInear 1.77) is particularly bright because the center ofthe gem reflects light gathered from around the ob-server and returns that light to the observer. Yet theouter areas window slightly, and in lighter coloredgems this is distracting. This view can be explainedby looking at the color-coded contrast map (AG withwhite contrast map). Red and green indicate higher-contrast areas that provide some brightness in thoseparts of the gem. Note that these extend out to thegirdle, which is very important. The outer areas con-tain blue, resulting from lower-angle lighting. Theouter white areas are the windows where the ob-server sees through the gem.

Figure 18B: When gently rocking this apatite (RInear 1.64), the observer sees much of their own darkreflection in the middle. The apparently bright outeredges in the photograph of the stone are actually dull;the observer sees through the gem. This produces astone that is not very attractive or visually dynamic.The black area of the color-coded contrast map (AG

Figure 17. For this sample gemstone, there is little black (retro-reflection of the observer) in the AG environment.Red reflection (70°–83° arc) is arranged in a narrow, wagon-wheel pattern from the girdle edge to the near-center.Red will be bright when the gemstone is held at some distance, but dark if the gem is close to the observer. Theevenly distributed green shows where light is returned from around the observer’s head (55º–70º arc). Violet (40º–55º arc) comes from a low angle on the horizon and is generally dark. The lowest angles (0º–40º arc) would be seenas light blue. Together, these work to compose a uniformity of varying contrasts within the gem.


with white contrast map) is a reflection of the ob-server. Red and green indicate higher contrast areasof brightness, and some of the outer areas containdull blue-green, resulting from lower-angle lighting.Again, the outer white areas are windows.

The next two examples show better cut optimization:Figure 18C: Despite this amber’s soft appearance

(RI near 1.54) caused by facets that are slightlyrounded and less crisp, its brightness—even whenrocked—comes from effective use of high-angle entrylight to provide dynamic contrast and minimal ob-server reflection (black). In the red areas of the map,the observer’s reflection may come into view whenthe gem is slightly tilted. The prominent green areasrepresent a large amount of bright light entering thegem. The even distribution of red and green fromculet to girdle adds to the attractiveness. Minimalareas of blue (lower-angle lighting) and white (win-dowing) keep this gem bright.

Figure 18D: This grossular garnet (RI near 1.74) isbright and does not window easily, even whenrocked. Its brightness comes from the effective useof high-angle light entry to create a good mix of dy-namic contrast, with little reflection of the observer.Red areas indicate that when the gem is slightlytilted, the observer’s reflection may come into view.The abundance of green areas helps by directingbright light into the gem. For maximum visual ap-peal, the red and green areas should be evenly distrib-uted and extend from culet to girdle. In this map,there is little blue (lower-angle lighting) or white(windowing).

APPLICATION TO GEMCAD-BASED OR 3-D WIREFRAME DESIGNSThe following discussion provides examples of how toread and interpret the AG contrast maps to optimize

cutting schemes. Six different GemCad designs specif-ically for quartz (or other gems with an RI near 1.55)were chosen from the DataVue file of GemCad de-signs. The name of the design, the creator, and the pub-lication where it first appeared are listed. Each showsa table where the pavilion depth and crown heightchange by 1% of girdle width (and all pavilion andcrown angles change accordingly). The resulting anglescan be obtained from the GemCad file, but for simplic-ity this article uses crown and pavilion percentage dif-ferences. The table size is constant, as altering it wouldresult in many more combinations. The original de-sign’s proportions are outlined and marked “original.”For reference, the graphic design is also shown, accom-panied by a contrast plot for an idealized round bril-liant. The idealized contrast plot demonstrates thetypes of color distribution that contribute to effectivedesigns. It serves as a visual reference for the types ofdominant colors and balance that might be desired.

Design 13022 (figure 19): This design performs wellwith a variety of angle differences. It is a very forgivingdesign that can be used with a variety of crown heightsto better utilize the rough. But note that all of thesecontrast plots have a predominance of green in themiddle. Where does the contrast belong? Green repre-sents brightness, but brightness alone is not terriblyinteresting. For more visual interest, a cutter could trya 46% pavilion/21% crown or a 47% pavilion/12%crown modification to add contrast. As mentioned be-fore, trying several patterns will help identify whichspecific elements are the brightest and most attractive.

Design 13061 (figure 20): This example demon-strates the need for caution in trusting a cutting plan,regardless of the source. The original gem is fairlydull, perhaps due to a typographical error in the plan,a design not meant for quartz, or incorrect enteringof the angles. While a large amount of red around the

Figure 18. Four gem-stones from GIA’s Dr.Eduard J. Gübelin Col-lection were scannedusing a non-contact op-tical measuring deviceto obtain a 3D image ofeach. Photos showingthe representative pat-terns when viewed face-up are equated to theAG contrast maps de-rived from DiamCalc.

A B C D


girdle edge does not always produce the best design,the 41% pavilion/11% crown combination may pro-vide the most contrast, with some blue at the girdleedge to break up the red.

Design 13096 (figure 21): This design offers

abundant contrast, and the resulting gemstonewould be quite dynamic. Whereas the contrastareas with combinations of red and red/black canslightly darken the stone, green/red is generally abetter combination. Designs should minimize blue

Figure 19. In this design, the six center pavilion main facets tend to gather light from the same direction, withoutbreaking it up much (seen here as large green center areas). For more visual interest, a cutter could try a shallowercrown and pavilion, which would give it more contrast into the center.

London ShieldNorman Steele, Seattle Facet Design, Oct. 1988, p. 3PAVILION DEPTH %44% 45% 46% 47% 48% 49% 50%

11%

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points in the center. For this design, a 45% pavil-ion/11% crown or 41% pavilion/17% crown wouldbe more effective.

Design 13138 (figure 22): Of the triangular designschosen for these illustrations, this is probably the

most dynamic example. It is another forgiving designand also has high contrast all the way into the middleof the stone, with greens and reds throughout. Whilethe original proportion set has a little too much bluein that quadrant of the plots, it would still produce a

Figure 20. This design is fairly dull, and a much steeper pavilion and shallow crown would dramatically improveits appearance.

Barion Old Mine TriangleBen Dawson, Facets, June 1989PAVILION DEPTH %36% 37% 38% 39% 40% 41% 42%

10%

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very good appearance. Slightly increasing the paviliondepth—for instance, 47% pavilion/14% crown—would improve the design.

Design 13141 (figure 23): Note the prominence ofred among these choices. The red areas start to pickup reflections of the observer (black areas) when

slightly tilted, sometimes darkening the stoneslightly. Therefore, this design should not be usedwith dark material, and only with slightly light ormedium colors. The original angle combinationsoffer a good balance between contrasts of differentlight-entry angles. If the material is slightly dark, a

GemFaire 94Jim Summers, New Mexico Facetor, Aug. 1994PAVILION DEPTH %40% 41% 42% 43% 44% 45% 46%

9%

10%

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13096DATAVUE #

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Figure 21. This design presents high contrast. The cutter merely needs to choose steeper pavilion angles (≥44%pavilion depth) and slightly shallower crown angles to avoid windowing.


44% pavilion/12% crown will produce a little lessdarkness in the stone.

Design 13146 (figure 24): Note that this gem has anarrow range of feasible pavilion depth. At 45%, thereis strong windowing, which also occurs in the whitearea in the 46% column. While not shown here, tilting

the example in the 46% column will also produce win-dowing. At 50%, the substantial amount of blue (low-angle light entry) does not allow much brightness. Theoriginal proportions will work very well, but higherproportions of green in a contrast map—for instance,48% pavilion/17% crown—are generally preferable. To

TrilogyRobert Strickland, TFG Newsletter, Oct.-Dec. 1996, Vol. 17, No. 4, p. 18PAVILION DEPTH %43% 44% 45% 46% 47% 48% 49%

11%

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Figure 22. This is a forgiving design with high contrast into the center. With pavilion depths from 43% to 49% anda crown ranging from 12% to 17%, all working effectively, this design can be adapted to shallow or thick rough.


achieve good contrast, the adjoining facets need to haveoffset angles. This design only does so in a very narrowrange of proportions.

Computer modeling can assist in effective designby simulating the best angle combinations and/or

modifying the design (adding or removing facets, orchanging their placement). By using lighting schemessuch as AG and ASET in design planning, facetarrangement can be optimized to produce the mostvisually interesting results.

Brazil Cushion Triangle 1Richard C. Walker, Facets, Sept. 1988, p. 3PAVILION DEPTH %44% 45% 46% 47% 48% 49% 50%

9%

10%

11%

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13141DATAVUE #

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Figure 23. Another forgiving design with high contrast, this should be used with lighter materials. The red areasstart to pick up reflections of the observer when the stone is tilted, darkening its appearance.


GENERAL CUTTING CONSIDERATIONS1. Designs for equal-sided gems (e.g., square, round,

equilateral triangular) can easily be made moredynamic. Elongated shapes are inherently moredifficult to optimize to the same degree.

2. Step cuts are more difficult to optimize. Withthe addition of four or more rows on the pavil-ion, the difficulty increases. In optimizing stepcuts, very careful attention must be paid to stepwidth, as well as the design execution.

Figure 24. This design is effective in a limited range of proportions and should be used with lighter materials.

Third MillenniumErnie Hawes, New Mexico Facetor, Nov.-Dec. 1999PAVILION DEPTH %45% 46% 47% 48% 49% 50% 51%

9%

10%

11%

12%

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ORIGINAL

3. Some designs are more effective for certain RIranges than others. For example, the standardround brilliant is far more effective for gemswith a high RI (diamond, zircon, etc.) than forlower-RI materials.

4. The gem’s physical size also dictates designconsiderations. For example, when cutting a 10mm gem, a simple single-cut design with eightpavilion and eight crown facets (plus the tablefacet) is not as effective as a 57-facet round bril-liant design. A 181-facet design, for instance,does not succeed unless the gem is of substan-tial size, because tiny facets are less distinctand look “fuzzy.”

5. Adding small facets to designs that containlarge facets is rarely practical. For example,splitting stars into three small facets whileleaving the others at a normal size will have lit-tle effect and may actually diminish the design.Often that center facet provides less contrastthan if there were only two facets.

6. Every now and then, faceters concern them-selves with dispersion, which jewelers referto as “fire.” It is a measurement that indi-cates how much light is spread by differentmaterials. Generally, lower-RI gems do notcontain much visible fire. Adding color satu-ration to the material hides what little firemight be there. On the other hand, highly dis-persive gem materials (with dispersion valuesabove 0.039) provide some unique opportuni-ties to display fire. This effect depends on twoconsiderations:

a. Lighting environment: Where the lighting isprimarily diffused (e.g., reflected from awhite ceiling with no direct spot-type

source directed at the gem), the observerwill see little fire. If the lighting environ-ment provides strong contrast, using brightspot-lighting against a dark background, fireis strongly enhanced.

b. Strong contrast: Areas of strong contrast inthe gem will create fire as those areas alter-nate between dark and bright when the gemis rotated. Figure 25 shows a gem being ro-tated in 2º increments with the light sourcein a fixed position. As the gem is rotated, themovement of facets causes them to fluctu-ate between dark and light. At the thresholdbetween light and dark, the observer will seefire. If the gem is moved slowly, with facetsonly slightly changing in relation to thelight source and the reflection to the eye, thechange in color of the facet will be gradual.If movement is sudden, the observer mayonly see where the facet is dark and thenlight, without seeing the fire. When a facetonly slightly darkens or lightens, fire isfaint.

Following these rules for optimization, such ascreating a design with strong contrast, will alsoimprove the appearance of a gem and increase itsfire.

Before implementing personal preferences, thefaceter should be aware that the colored gem marketis very focused on color: hue, saturation and tone.Color quality is critical, but often suffers in lightlycolored gems when the design is modified towardbrightness. Instead, optimization may be needed toenhance the color first and foremost, with scintilla-tion a secondary priority. Understanding the ele-ments of brightness can help the faceter achieve itwithout compromising color.

Figure 25. Each image shows a 2º rotation clockwise from the previous image. A spot light source contributes asmall amount of fire (seen here as red, blue, green, or yellow virtual facets). As the gem is rotated, some virtualfacets go from light to dark (examples are circled). As a facet nears the border between light and dark, the observerwill see fire. Some of these flares of color last through larger degrees of rotation than others (larger red circles).While not illustrated, when a facet only slightly darkens or lightens, fire is faint. Strong changes in contrast createstronger fire. More fire is exhibited by materials of higher dispersion values.



ABOUT THE AUTHORMr. Gilbertson is the project manager of cut research for GIA inCarlsbad, California.

ACKNOWLEDGMENTSThe author acknowledges Dr. Ilene Reinitz for her many helpful

suggestions and the organization of this paper. The author greatlyappreciates comments and suggestions about content from DaleCarriere, Lisa Elser, Nathan Renfro, Michael Cowing, and WayneEmery.

Albert M.K. (1995) Genericity and the Perception of Visual Con-tours and Surfaces. Ph.D. dissertation, University of California,Irvine, p. 25.

Caudill J., Sasian J., Yantzer P. (2008) Methods, apparatus, and sys-tems for evaluating gemstones. US Patent number: 7336347,filed Dec 20, 2004, issued Feb. 26, 2008.

Cowing M. (2009) Describing diamond beauty—assessing the op-tical performance of a diamond. ACA Gem Laboratory,http://www.acagemlab.com/articles/Describing.htm [date ac-cessed: Aug. 30, 2012].

Gilbertson A. (2003) Device for judging symmetry, brightness, andefficacy of light return in precious stones. U.S. Patent 6665058,filed May 24, 2000, issued Dec. 16, 2003.

Harding B. (1975) Faceting limits. G&G, Vol. 15, No. 3, pp. 78–88.Hoffman D. (1998) Visual Intelligence: How We Create What We

See. W.W. Norton & Co, New York, NY.GIA (2006) Diamond Grading Lab Manual. Gemological Institute

of America, Carlsbad, California, p. 21.Kanizsa G. (1955) Margini quasi-percettivi in campi con stimo-

lazione omogenea [Quasiperceptual margins in homogenously

stimulated fields]. Rivista di Psicologia, Vol. 49, No. 1, pp. 7–30. Translated by W. Gerbino, in Petry and Meyer, 1987, pp. 40–49).

Petry S.J., Meyer G.E. (1987) The Perception of Illusory Contours.Springer-Verlag, New York, NY.

Purves D. (2011) An empirical explanation: Simultaneous brightnesscontrast. Center for Cognitive Neuroscience, Duke University,http://www.purveslab.net/research/explanation/brightness/brightness.html [date accessed: Aug. 30, 2012].

Reflector technologies (undated) Good Old Gold, www.goodoldgold.com/technologies/reflectortechnologies/history [date accessed:June 5, 2013].

Sarcone G., Waeber M.-J. (undated) Colors of the mind,http://www.archimedes-lab.org/color_optical_illusions.html[accessed on Aug. 30, 2012].

Sasián J., Quick J., Sheffield J., Caudill J., Yantzer P. (2007) Evaluationof brilliance, fire, and scintillation in round brilliant gemstones.Optical Engineering, Vol. 46, No. 9, p. 60936014–6093625.

White M. (1979) A new effect on perceived lightness. Perception,Vol. 8, pp. 413–416.

REFERENCES

gia.edu/gems-gemology

For online access to all issues of GEMS & GEMOLOGY, visit:

82 FLUORESCENCE PRODUCED BY OPTICAL DEFECTS IN DIAMOND GEMS & GEMOLOGY SUMMER 2013

Fluorescence is the emission of electromagneticradiation (e.g., visible light, ultraviolet light, X-rays, and gamma rays) from a substance, stimu-

lated by the absorption of incident electromagneticradiation. The emission persists only as long as thestimulating radiation is continued. The terms fluo-rescence and photoluminescence often appear inter-changeably, but gemologists commonly use theformer to describe the visible light emission from ul-traviolet (UV) excitation. In most cases the emittedlight has a longer wavelength, and therefore lower en-ergy, than the absorbed radiation. Diamonds contain-ing no defects or impurities generally do not absorbvisible and UV light (>230 nm) and thus produce nocolor or fluorescence. But when impurities or defects(often referred to as color centers) are present, theymay absorb visible and UV light to produce color, flu-orescence, or both. In diamonds with multiple colorcenters, the fluorescence from one defect may evenexcite the emission from another center more effi-ciently than the external UV light. Conversely, the

fluorescence from one color center may be absorbedby other defects, dramatically reducing the overallfluorescence. Phosphorescence commonly refers tovisible light emitted by a diamond after the stimu-lating UV light source has been discontinued. Whilerelated to fluorescence, it is a relatively uncommonvisual property of gem diamonds and not a focus ofthis study.Fluorescence in diamonds has been studied for

nearly a century (e.g., Becquerel, 1868; Mani, 1944;Shipley, 1947; Wild and Biegel, 1947; Cotty, 1956;Dyer and Matthews, 1958; Collins, 1974, 1982; Fritschand Waychunas, 1994; Eaton-Magaña et al., 2007; Hol-loway, 2009; Shigley and Breeding, 2013). While muchis known and published about diamond defects andfluorescence, most gemologists do not have ready ac-cess to this information. This article seeks to clearlyoutline the defects that cause fluorescence in dia-mond, and explain how the gemological tools used toevaluate this property may impact observations. Fordecades, investigations of diamond fluorescence havemainly focused on visual observation (Moses et al.,1997; figure 1), while more recent studies have dealtwith individual spectra and the physics of individualdefects. The application of 3D fluorescence spec-troscopy has been limited. Eaton-Magaña et al. (2007)

FLUORESCENCE PRODUCED BY OPTICALDEFECTS IN DIAMOND: MEASUREMENT,CHARACTERIZATION, AND CHALLENGESYun Luo and Christopher M. Breeding

FEATURE ARTICLES

Three-dimensional fluorescence spectra were collected from both natural-color and treated diamondswith common color centers (including N3, H3, H4, 480 nm, and N-V) to characterize the fluorescenceproduced by each defect. Unlike individual spectra, 3D presentations of multiple spectra allow quickand simultaneous determination of the fluorescence-producing defect(s), the excitation energy that yieldsmaximum fluorescence intensity, the variation of fluorescence with excitation, and the peak positionand band shape of individual and overall fluorescence emissions. The combination of 3D fluorescencespectra from common defects and emission spectra from several standard ultraviolet light sources re-vealed noticeable inconsistencies in the fluorescence observed. Our data indicate that variations in UVlamp output can significantly affect the fluorescence color observed in gem diamonds.

See end of article for About the Authors and Acknowledgments.GEMS & GEMOLOGY, Vol. 49, No. 2, pp. 82–97,http://dx.doi.org/10.5741/GEMS.49.2.82© 2013 Gemological Institute of America

presented a few spectra for diamond in this format,and Hoover and Theisen (1993) investigated other col-ored gemstones with this approach. Visual evaluation of fluorescence is standard prac-

tice in gemological laboratories, and fluorescencecolor and intensity are often documented on labora-tory reports. When selecting diamonds, jewelers alsorely on fluorescence to ensure a good color matchunder a variety of lighting circumstances. The mostcommon excitation source is a handheld UV lamp,which often has dual modes for long-wave (LW) andshort-wave (SW) UV radiation. The typical color cen-ters in diamond fluoresce more intensely underLWUV excitation. Fluorescence assessment reliesmainly on visual observation at room temperature—fluorescence can vary in intensity and color at differ-ent temperatures—and sometimes requires a set ofreference diamonds for comparison. Observation offluorescence can be affected by three main factors: (1)the nature of the emission from the UV light source;(2) the nature of the defect(s) responsible for the fluo-rescence; and (3) methodology, including the viewinggeometry and the distance from the radiation source.Within current industry practices, complications existfor each of these factors.First, the excitation produced by different light

sources may vary and not consist of “pure” LWUVor SWUV light, which generally have wavelengths of365 nm and 254 nm, respectively. Differences in ex-citation wavelengths between lamps may produceinconsistent fluorescence reactions. Warm-up time,

the materials used in the UV filters, and aging oflamps and filters can also affect the radiation output.Secondly, multiple defect centers may exist withinthe same diamond and produce different emissionpeaks simultaneously. To the human eye, multipleemissions combine to produce a single, albeit mixed,fluorescence color (e.g., blue + yellow = apparentwhitish fluorescence). Visual evaluation of fluores-cence does not allow for identification of multipledefects or irregular emission peaks. Finally, the dis-tance between the radiation source and the diamondas well as the stone’s orientation (table-down versusface-up) may produce noticeably different fluores-cence by changing the amount of excitation energythat interacts with the diamond.In this study, a high-resolution luminescence

spectrometer was used to study fluorescence emis-sions from common color centers in gem diamondsby obtaining three-dimensional scans of excitation,emission, and fluorescence intensity. From the 3Dscans, we can quickly and simultaneously determinethe nature of observed fluorescence and the energyat which the fluorescence maximizes or changes bysystematically varying the excitation energy wave-length. Furthermore, emission characteristics suchas peak position and band shape that are characteris-tic of particular defect centers can be evaluated. With detailed, direct knowledge of fluorescence-

producing diamond defects in hand, we surveyed sev-eral common UV light sources to better understandhow much variability exists in UV excitation and to

FLUORESCENCE PRODUCED BY OPTICAL DEFECTS IN DIAMOND GEMS & GEMOLOGY SUMMER 2013 83

Figure 1. For decades, UV lamps have been used in the jewelry industry and by gemological laboratories to assessdiamond fluorescence. Left: A gemologist examines fluorescence reactions from a suite of colorless faceted dia-monds in a long-wave UV fluorescence box. Right: A group of rough stones illustrates the range of fluorescence col-ors seen in diamond under LWUV excitation. Note that GIA evaluates fluorescence of individual stones, not inbulk as shown here. Photos by Eric Welch.

further investigate the effect of UV source on observedfluorescence colors. While a few previous articles havemade similar investigations (e.g., Eaton-Magaña et al.,2007; Pearson, 2011), our survey includes newer LED-based sources that have only recently seen widespreaduse in the industry. The outcome of this study couldbe beneficial to both the diamond industry and gemo-logical laboratories in that accurate, consistent, andreproducible fluorescence measurements are vital forindustry confidence. In addition, better methods formeasurement of fluorescence from different defectcenters may lead to more effective methods of detec-tion and separation of natural, synthetic, and treateddiamonds.

MATERIALS AND METHODSSamples. Three-dimensional fluorescence spectrawere collected from 25 faceted diamonds, including19 natural-color samples and six treated by high-pres-sure, high-temperature (HPHT) and irradiation (table1). GIA issues reports on thousands of colored dia-monds each year, providing a large selection of sam-ples. The diamonds in this study, all of which carriedGIA reports indicating natural- or treated-color ori-gin, were chosen as representative of their respectivedefect group. While multiple fluorescence-producingcolor centers occur in most diamonds, each of oursamples was dominated by one of the following:

1. N3 center 2. H3 or H4 center 3. 480 nm band 4. N-V center

Emission Spectra from Industry UV Light Sources.To evaluate the excitation energy produced, we col-lected emission spectra from various UV lightsources over the 200–900 nm range using an OceanOptics USB 2000 CCD spectrometer with a UV-transmitting fiber-optic cable. Output spectra fromfive UV sources—including a GIA UV lamp (model

745000), a custom-made GIA fluorescence measure-ment device with UV LEDs (not shown), a handheldUVP Mineralight hobbyist lamp, a UV LED loupe,and a commercial 365 nm LED light source (figure 2,A–D)—were measured and output peak positionswere recorded.

3D Luminescence Spectroscopy.A Thermo AmincoBowman II (ABII) luminescence spectrometer (figure


Figure 2. UV light sources fromthis study include (A) a standardgemological UV lamp, (B) the Min-eralight hobbyist lamp, (C) a com-mercial UV fluorescence loupe, (D)a fiber-optic LED light source, and(E) the Thermo ABII luminescencespectrometer. Photos by Eric Welch(A) and Christopher M. Breeding(B–E).

In Brief • 3D fluorescence spectra allow quick, simultaneous char-acterization of the excitation energy that maximizes fluo-rescence, variation in fluorescence with excitation, aswell as position and band shape of individual and overallfluorescence emissions.

• Common mercury-based UV lamps and LED-based UVloupes do not produce pure 365 nm LWUV emissions.

• UV lamp output variation can significantly affect fluores-cence color and intensity observed in diamond.

• A standardized UV excitation source is necessary for ac-curate and reproducible determination of fluorescence.

2E) was used to investigate the samples’ fluores-cence. The analyses were conducted at room tem-perature to simulate typical observation conditions.Three-dimensional fluorescence spectra wererecorded in the 300–750 nm emission range (2 nmresolution, 4 nm bandpass) using an excitation of220 to 500 nm (5 nm intervals, 4 nm bandpass). De-tector voltage was adjusted so that the highest peakin the spectrum comprised 80%–90% of the instru-ment’s maximum fluorescence intensity range. TheABII spectrometer is not configured with excitationfilters, so most of the 3D spectra collected containedfirst-, second-, and sometimes third-order artifactsproduced by the spectrometer grating at 1×, 2×, and3× the excitation wavelength. In most of the spectra

presented, the 2× and 3× artifacts have been re-moved. The 1× artifact was retained to avoid poten-tial data loss.Each 3D scan took approximately four hours to

complete and consisted of 57 individual spectra. Theadvantage of a 3D plot is that all aspects of excitationand emission can be derived. Any of the 57 fluores-cence emission spectra for a given excitation can beseparated, and data for excitations not specifically an-alyzed can be interpolated. In addition, photolumi-nescence excitation (PLE) spectra for a givenemission wavelength can be obtained to see the ef-fect of excitation light frequency on fluorescence.Figure 3 illustrates these features in the anatomy ofa 3D fluorescence spectrum.


Figure 3. Top left: 3D fluorescence spectra are composed of many individual fluorescence spectra collected at dif-ferent excitation wavelengths. This example from a colorless diamond containing N3 defects (sample 2) showshow a single spectrum (top left, blue line) at a given excitation (365 nm) can be extracted and examined in detail(bottom left). PLE excitation spectra can also be extracted from the 3D data (top left, red line and bottom right).Top right: Absorption (UV-Vis) and PL emission spectra confirm the presence of a defect such as N3 and relate tothe data taken from a 3D spectrum. Fluorescence (bottom left) and PL (top right, blue line) emissions from the de-fect are similar and longer in wavelength than the ZPL, whereas PLE (bottom right) and UV-Vis absorption spectra(top right, red line) correlate and show defect-produced bands at wavelengths shorter than the ZPL.

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PL Intensity (counts)Fluorescence Spectroscopy

Additional Absorption and PL Spectroscopy.Ultravi-olet/visible/near-infrared (UV-Vis-NIR), Fourier-transform infrared (FTIR), and photoluminescence(PL) spectra were collected to complement the fluo-rescence data, providing additional detail about thedefects under more readily measurable conditions(again, see figure 3). UV-Vis-NIR spectra were col-lected with an Ocean Optics integrating sphere andHR 4000 CCD spectrometer over the 380–1000 nmrange (~1 nm resolution) at ~77K temperature. FTIRspectra (not shown) were collected to identify dia-mond type using a Thermo Nexus 6700 FTIR spec-trometer (6000–400 cm–1, 1 cm–1 resolution, 128scans, room temperature). Breeding and Shigley(2009) describes diamond type and its use in gemol-ogy. Photoluminescence spectra were collected usinga Renishaw inVia Raman microscope (325, 488, 514,633, and 830 nm laser excitations, various scanranges, and ~77K temperature).

RESULTSUV Light Sources. GIA UV Lamp. Gemologists useconventional UV lamps (figure 2A) to observe astone’s fluorescence color in response to long- orshort- wave radiation. The lamps in this study weresold by GIA Instruments until 2009 and are stillprevalent in the trade. It is well known that tradi-tional UV lamps do not provide single characteristic365 nm (LWUV) and 254 nm (SWUV) emission lines(Williams, 2007; Pearson, 2011) due to the variety ofmaterials used in UV filters and the aging of lampsand filters. Rather than a single 365 nm emissionpeak, LWUV lamps often emit 404 and 435 nm linesand a broad band that extends from the UV to the vis-ible region of the spectrum. Similarly, SWUV lampsalways have distinct peaks at 254, 315, and 365 nminstead of a single 254 nm emission. All of theseemission lines, as well as several weaker ones, areproduced by the mercury lamp inside the units. Thefilter materials used to remove mercury radiation arenot 100% efficient and leak undesired emissions. Asthe filters age, the leaked emissions become strongerand more prominent.Examination of two handheld UV lamps manu-

factured by GIA and used at its laboratory revealed amajor peak at 368 nm (FWHM = 17 nm) with LWUVexcitation, accompanied by a small peak at 404 nm(figure 4A). In addition to the 252 nm (FWHM = 3nm) SWUV emission, which shifted 2 nm from typ-ical 254 nm SWUV, there were major peaks at 312,365, 404, and 435 nm, as well as minor peaks at 296,302, and 334 nm. Interestingly, the peak intensity at

365 nm (the typical LWUV emission) was more in-tense than the 252 nm SWUV peak (figure 4B), likelydue to filter aging. The existence of this intense 365nm peak in the excitation may have a pronouncedeffect on what is observed as SWUV fluorescence. Be-cause most gemologists use UV lamps for manyyears and never replace the filters, these tests are rep-resentative of industry practices.

UVP Mineralight Lamp.The UVP Mineralight is an-other dual LW-SW lamp widely used in the industryand by hobbyists (figure 2B). Though similar in ap-pearance and function to the GIA UV lamps, thislamp showed different results. LWUV excitation pro-duced an intense broad band at 355 nm, along withthe primary LW peak at 365 nm (FWHM = 37 nm)and weak emissions at 313, 405, and 437 nm. Short-wave excitation showed a similar array of peaksusing the GIA lamp, with major emissions at 254(FWHM = 4 nm), 313, and 366 nm, as well as minorpeaks at 297, 303, 335, and 405 nm (figures 4C and4D). Note: Both the GIA and Mineralight lamps are

able to produce LWUV and SWUV because they con-tain low-pressure mercury lamps that emit initiallysharp mercury lines, but the phosphors inside thelamp are creating a conversion to broadband wave-lengths at a longer wavelength. The lamps emit arange of light that spans both LWUV and SWUV.They are equipped with a daylight filter that removesmost of the visible light so that mainly the desiredUV band passes through the filter (R. Geurts, per-sonal communication, 2012).

Digital GIA LED Fluorescence Device. GIA uses acustom-made fluorescence meter with LWUV LEDsto measure the fluorescence intensity documentedon its diamond grading reports. Designed to improvefluorescence measurement consistency, this instru-ment uses an LED excitation source with a singleemission peak at 367 nm and an FWHM of 14 nm(figure 4E).

UV LED Loupe. A generic commercial UV loupesometimes used in the trade (figure 2C) was also ex-amined. The LED excitation source from this loupegave a single peak at 403 nm with an FWHM of 17nm (figure 4F).

Commercial LED Light Source. For comparison withthe other LED sources, we also tested a commer-cially available “365 nm” LED light source manufac-tured by Ocean Optics (figure 2D). This excitation



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Figure 4. The UV light sources from this study showed clear differences in emission characteristics.

source showed a single peak at 364 nm with anFWHM of 10 nm (figure 4G).

ABII Excitation Light Source.The ABII spectrometer(figure 2E) was selected to provide well-constrained,high-resolution fluorescence spectra. To understandhow its excitation compared to that of other sources,different excitation wavelengths of the ABII CWXenon source were examined (the instrument canproduce excitation of 200–950 nm). As shown in fig-ures 4H and 4I, when the instrument was set to 365nm excitation with 4 nm bandpass, the resultant

emission showed a narrow peak at 366 nm with anFWHM of 5 nm. With a 16 nm bandpass parameter(which most closely resembled the output of a GIALW-UV lamp), a peak was observed at 367 nm withan FWHM of 15 nm. To precisely characterize thefluorescence from a given excitation wavelength, wechose the smallest available bandpass setting (4 nm),and thus the narrowest excitation emission, for the3D-fluorescence spectra collection.

N3 Center. The N3 center is the most commoncolor-producing defect in diamond, consisting of a va-


TABLE 1. Diamonds examined in this study.

Sample Natural color Colora Weight Shape LWUV SWUV Prominentor treated (ct) reactionb reactionb color center

1 Natural Colorless (D) 1.10 Round Medium green None

2 Natural Colorless (D) 0.37 Round Strong blue Medium green

3 Natural Colorless (E) 0.31 Round Medium blue None

4 Natural Near-colorless (I) 1.12 Round Strong blue Weak green N3

5 Natural Near-colorless (I) 1.51 Round Strong blue Weak green

6 Natural Faint yellow (L) 1.01 Cushion Strong blue Medium green

7 Natural Very Light pink 1.02 Heart Strong blue Medium blue

8 Natural Fancy Light greenish yellow 0.14 Round Strong yellow Medium yellow

9 Natural Fancy yellow-green 0.69 Round Strong blue + Medium blue +yellow (uneven) yellow (uneven)

10 Natural Fancy Intense greenish yellow 1.01 Heart Medium to strong Weak yellow H3yellow + blue

11 HPHT-treated Fancy Vivid green-yellow 2.34 Round Strong green + Medium greenweak blue

12 Natural Fancy Intense yellowish green 3.10 Rectangle Very strong green Strong green

13 Natural Fancy Light yellow-green 0.58 Round Strong green Strong green H4

14 Natural Fancy Light yellowish green 1.04 Round Strong green Medium green

15 Natural Fancy Deep orange-yellow 0.40 Round Strong yellow Medium yellow

16 Natural Fancy Deep brownish 1.62 Pear Strong orange Medium to strongorangy yellow orange

17 Natural Fancy Vivid yellow-orange 0.72 Pear Strong orange Strong orange 480 nm band

18 Natural Fancy Intense orange-yellow 1.02 Marquise Strong orange Strong yellow

19 HPHT-treated Fancy Intense orangy yellow 0.19 Round Strong yellow Medium yellow

20 HPHT-treated Fancy Intense yellow 0.39 Round Strong orange Medium orange(partial)

21 Natural Fancy brown-pink 1.51 Old Mine Weak red Weak to medium red

22 Natural Very Light pinkish brown 2.01 Pear Very weak orange Very weak orange

23 HPHT-treated Fancy red 1.49 Square Weak red Medium redand Irradiated N-V

24 HPHT-treated Fancy Deep pink 0.90 Oval — —and Irradiated

25 Irradiated Fancy red 0.17 Round Strong red Very strong red

aAssigned using standard GIA color grading practices.bLWUV and SWUV reactions were observed using excitation from a standard handheld UV lamp.

cancy surrounded by three nitrogen atoms on a {111}plane. The zero phonon line (ZPL), the identifyingemission for N3, occurs at 415 nm. This line, alongwith a broadband emission with dominant peaks at429, 439, and 450 nm, results in typical blue fluores-cence (Collins, 1982).

Absorption and PL Spectroscopy. UV-Vis-NIR spec-tra for samples 1–7 all showed the N3-related ZPLat 415 nm. Sample 7 also showed a 550 nm band,which causes the stone’s pink bodycolor. FTIRanalysis identified them as type Ia diamonds withboth A and B nitrogen aggregates in various concen-trations. Samples 1 and 3 showed more A aggregates,which are known to quench fluorescence (Collins,

1982), possibly explaining the weaker fluorescenceobserved (table 1). PL spectra confirmed the pres-ence of N3 in sample 2 (figure 3). The 503.2 peakin the PL spectra of samples 1, 3, and 7 revealed anH3 center as well. The H3 center in sample 1 wasthe source of the visible greenish component of thefluorescence.

Fluorescence Spectroscopy. Among the seven dia-monds examined in this category, six have color inthe D-to-Z range (colorless to pale yellow) and one hasa light pink color (figure 5). All seven showed rela-tively intense fluorescence emission, with the ZPL at415 nm and three peaks at 429, 439, and 450 nm su-perimposed on a ~400–550 nm broadband, all charac-


Figure 5. Diamondswith N3 defect centersinclude samples 1–3,which are colorless (1and 3 have a brownishhue); samples 4–6,which are near color-less to faint yellow (notshown); and sample 7,a pink diamond withboth N3 and H3 defectcenters. Samples withthe H3 center (8–11)and H4 center (12–14)are yellow to lightgreen. Diamonds withthe 480 nm band (15–20) are yellow to or-ange, while those withN-V centers (21–25) arepale to intense pink orred. Photos by DonMengason and RobisonMcMurtry.

teristic of the N3 center (Eaton-Magaña et al., 2007).The 3D fluorescence spectra indicated that this N3-related emission reaches its maximum at 395 nm ex-citation energy and is not excited above 430 nm(figure 6). Figures 6A and 6B show fluorescence spec-tra collected on sample 2 but with different bandpasssettings (4 and 16 nm). From these two spectra, it isclear that the bandpass does not affect the position ormaximum intensity of N3 fluorescence. Similar re-sults occurred for other defects. Although the band-pass of 16 nm most closely resembles the output of ahandheld LWUV light source, the 4 nm bandpass cho-sen for all the 3D fluorescence spectra in this studyadequately represented the corresponding excitation.Aside from the N3-related emission, which is not

active with excitation energy above 435 nm, sample7 showed a 520 nm emission band with a maximumat 470 nm excitation. This feature is caused by the

H3 center, which was observed from photolumines-cence spectra in these three samples but not in theother four from this category. As stated earlier, mostdiamonds contain multiple color centers.

H3 and H4 Center. The H3 center consists of a va-cancy trapped at an A aggregate of nitrogen, whichgives an uncharged defect consisting of two nitrogenatoms separated by a vacancy—for instance, (N-V-N)0. Optical absorption at this center has a ZPL at503 nm and creates a yellow bodycolor in diamond,while also commonly producing green luminescencewith visible-light stimulation. The H4 center con-sists of four nitrogen atoms separated by two vacan-cies. It is created when a vacancy migrates throughthe diamond lattice and combines with a B aggregateof nitrogen. This center has a ZPL at 496 nm and typ-ically produces yellow color in diamond. Both H3


Figure 6. These 3D fluorescence spectra were collected from diamonds with N3 as the major defect center. The toptwo spectra are from the same sample using different excitation energy peak widths. Sample 7 (bottom left) con-tains both N3 and H3 centers. UV-Vis-NIR spectra (bottom right) confirm the particular fluorescence defects. Exci-tation artifacts are marked in blue.

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and H4 centers can occur naturally or during treat-ment (Collins, 1982).Seven diamonds were examined in this category,

including six samples determined by GIA to be nat-urally colored and dominated by H3 and H4 (threeeach), as well as one HPHT-treated diamond domi-nated by H3 (samples 8–14; figure 5). Sample 8 is aFancy Light greenish yellow stone that fluorescedstrong yellow under LWUV and medium yellowunder SWUV. Samples 9, 10, and 11 all have somecombination of yellow and green bodycolors and ex-hibited an uneven fluorescence with blue and yellowzones. Samples 12, 13, and 14 have yellowish greenbodycolors and showed very strong green fluores-cence under both long- and short-wave UV.

Absorption and PL Spectroscopy. UV-Vis-NIR spec-tra showed the H3-related ZPL at 503 nm for samples

8, 9, 10, and 11, as well as ZPL at 415 nm from theN3 center. The H3 defect requires the presence of ag-gregated nitrogen, making the occurrence of N3 insuch stones very likely. Samples 12, 13, and 14showed H4-related ZPL at 496 nm in the UV-Vis-NIRspectra. FTIR analysis identified sample 8 as type IaAdiamond, and samples 9, 10, and 11 as type Ia withboth A and B aggregates in various concentrations.Samples 12, 13, and 14 are type IaB diamonds. Strong503 nm peaks for samples 8, 9, 10, and 11 and 496nm peaks for samples 12, 13, and 14 in the PL spectrafurther confirmed the presence of dominant H3 andH4 centers, respectively (figure 7D).

Fluorescence Spectroscopy. The 3D fluorescencespectra of samples 8–11 show an emission maximumat 520 nm with a wide band extending from ~480 to650 nm, a feature that manifested itself as a green or


Figure 7. These 3D fluorescence spectra were collected on diamonds with H3 (samples 8 and 10) and H4 (sample12) as the major defect centers. Both H3 samples also contained weak N3 emissions. In the bottom right corner,PL spectra show the presence of H3 and H4 in the respective samples. Excitation artifacts are marked in blue.

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yellowish green fluorescence (figures 7A and 7B).This emission feature is caused by H3 and has a max-imum at 470 nm excitation. Unlike N3, the 503 nmZPL of H3 is not seen at room temperature. The N3-related fluorescence feature was also observed withvarious intensities due to different defect concentra-tions (figure 7B). The spectrum for 365 nm excita-tion, which most closely approximates the LWUVlamp, showed both H3 and N3 emissions at rela-tively low intensity. Fluorescence spectra from theHPHT-treated sample (11) were not noticeably differ-ent from those of other H3-dominated natural-col-ored samples. The 3D fluorescence spectra of samples 12–14

(see sample 12 in figure 7C) showed an emission peakcentered at 512 nm with a band from ~470 to 630 nmthat resulted in green color from H4 fluorescence.This emission feature increases at 395 nm excitationand maximizes at 470 nm. Similar to H3, the ZPL forH4 (496 nm) is not visible at room temperature butwas clearly seen in liquid nitrogen–cooled PL spectrafor these samples. Both H3- and H4-related fluorescence emissions

showed a broad fluorescence band at ~470 to 650 nm.But the H3 fluorescence peak is shifted to the higher-wavelength side and has a wider tail toward this di-rection, resulting in a yellowish fluorescence ratherthan the green fluorescence of H4 (figure 8).

480 nm Band. Although the structure of the 480nm band is not understood, it is known to be asso-ciated with yellow fluorescence in diamond. Six di-amonds with 480 nm bands in the UV-visibleabsorption spectra were examined (samples 15–20;figures 5 and 9). Four of the samples were naturallycolored, and two were HPHT-treated. Samples 15–19 had a combination of orange and yellow in body-color and fluoresced strong yellow to orange andmedium yellow to orange under long- and short-wave UV lamps, respectively. Sample 16 had abrownish color component as well. Sample 20 hadyellow bodycolor and showed strong orange andmedium orange fluorescence under long- and short-wave UV, respectively.

Absorption and PL Spectroscopy.UV-Vis-NIR spectrashowed the typical 480 nm absorption band for all sixsamples (figure 9D). FTIR analysis identified all ofthem as type IaA diamonds with traces of isolated ni-trogen. Sample 18 contained much higher concentra-tions of aggregated nitrogen impurities than the othersamples. PL spectra at 514 nm excitation showed a

wide band from 600 nm to more than 850 nm, typicalof diamond with 480 nm bands.

Fluorescence Spectroscopy. 3D fluorescence spectrafrom 480 nm-band diamonds are complex. All of thesamples showed two major features: (1) a wide bandcentered at ~653 nm (maximum shifts between 630and 655 nm) that maximized with 485 nm excitationenergy, and (2) a ~539 nm-band (maximum shifts be-tween 505 and 541 nm) that increased with 420, 345,and 285 nm excitation energies (figure 9, A–C). Thecombination of both bands ranged from ~500 to 700nm and produced yellow to orange fluorescencewhen excited by visible light (near-LWUV). The bandin the red part of the spectrum (630–655 nm) couldbe excited independently of the ~539 nm band usinglonger-wavelength light. The fluorescence from this


Figure 8. Fluorescence spectra collected at 470 nm ex-citation from H3 (top, sample 8) and H4 centers (bot-tom, sample 12) using the ABII luminescencespectrometer show distinct differences in emissionpeak position and distribution (represented by dashedlines). Excitation artifacts are marked in blue.

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feature is likely the same as the PL broadband seenafter excitation with a 514 nm laser. In general, theband’s intensity increased with the size of the 480nm absorption band. No clear correlations explainthe differences in the ~539 nm band. The two HPHT-treated samples showed no obvious systematic dif-ferences from the naturally colored samples.

N-V Center. The N-V center consists of a single ni-trogen atom adjacent to a vacancy in the diamondlattice. The center can exist in an uncharged state,(N-V)0 with ZPL at 575 nm, or in a negative chargestate, (N-V)– with ZPL at 637 nm. N-V defects arecommonly associated with orange and red fluores-cence (Collins, 1982).We examined five diamonds with N-V centers

(samples 21–25; figures 5 and 10): two naturally col-ored, two multi-treated, and one irradiation-treated.Samples 21 and 22 were brownish pink and very light

pinkish brown natural-color diamonds that showedweak orange to red fluorescence under both long- andshort-wave UV lamps. Samples 23–25 were red anddeep pink diamonds that had undergone combina-tion treatments (HPHT + irradiation + annealing;samples 23–24) or standard irradiation + annealingtreatment (sample 25). The treated diamonds exhib-ited red fluorescence under both LWUV and SWUVlights.

Absorption and PL Spectroscopy. The UV-Vis-NIRspectra of samples 21 and 22 featured a broad 550 nmband (thought to be caused by plastic deformation)that contributed to their pink color, as well as the (N-V)– center at 637 nm. FTIR indicated type IIa stoneswith no measureable nitrogen or hydrogen impuri-ties. PL spectra showed evidence for significant con-centrations of (N-V)0, H3, and (N-V)– defects (figure10D). For samples 23 and 24, UV-Vis spectra indicated


Figure 9. These 3D fluorescence spectra collected on diamonds with 480 nm visible absorption bands as the majordefect center vary considerably. In the bottom right corner, UV-Vis-NIR spectra show differences in the shape andintensity of the 480 nm bands. Excitation artifacts are marked in blue.

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an abundance of (N-V)– centers; FTIR identified themas type IaAB with traces of isolated nitrogen. PL spec-tra showed both (N-V)0 and (N-V)– centers as well asH3 defects. For sample 25, UV-Vis spectra indicatedthe presence of a strong (N-V)– center and FTIRdemonstrated a low concentration of type Ib isolatednitrogen defects. PL spectra showed both (N-V)0 and(N-V)– centers, together with H3 centers.

Fluorescence Spectroscopy. The 3D fluorescencespectra for most of the N-V center samples are com-plicated by multiple fluorescence-producing defects,sometimes as many as three. Both naturally coloredsamples (21 and 22; figure 10A) showed the fluores-cence emission feature of the (N-V)0 center, with ZPLat 575 nm and an emission band extending from 575to more than 700 nm with peaks at 586, 600, and 618nm. We also saw clear fluorescence from two defects:N3 (triplet peaks at 410–450 nm) and H3 (a 520 nm

peak that maximized at 470 nm excitation). Despiteits presence in PL spectra, fluorescence from (N-V)–

was not observed in these samples. Sample 21 alsodisplayed fluorescence of unknown origin at ~340–360 nm. The treated samples (23–25) contained boththe (N-V)0 and (N-V)– centers as overlapping bands,with the latter fluorescence band dominating at 660nm and extending beyond 750 nm (figures 10B and10C). Sample 25 (figure 10C) featured only N-V de-fects in the fluorescence spectrum, consistent withthe occurrence of mainly isolated nitrogen impurities(type Ib). Samples 23 and 24 contain aggregated ni-trogen impurities and, as expected, showed fluores-cence from N3 and H3 color centers.

DISCUSSIONUV Light Sources. Emissions from the widely usedmercury-based UV lamps (GIA and UVP Minera-light lamps) do not contain pure 365 nm LWUV and


Figure 10. These 3D fluorescence spectra collected on diamonds with N-V centers show combinations of severaldefect centers. In the bottom right corner, PL spectra from corresponding samples confirm the presence of N-V cen-ters. Excitation artifacts are marked in blue.

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99)

C

254 nm SWUV peaks, but instead show multiple ex-citation energies of widely varying bandwidths. Sim-ilarly, the popular LED UV loupe has a visibleemission of 405 nm, rather than the standard forLWUV (365 nm). The emissions from GIA’s LED flu-orescence meter and commercial LED light sourcesshow a well-constrained LWUV emission in the364–367 nm range. The variability in excitationwavelengths and bandwidths among commonlyused lamps and LED UV sources demonstrates thatthe colors and intensities of observed fluorescencein a single sample can vary depending on the lightsource. UV lamp emissions tend to fluctuate accord-ing to the age of the bulbs and filters as well aswarm-up times, making it very difficult to achieveconsistent results from one source to another. LEDsources are far more constrained in emission band-width and purity, but they are manufactured in sucha wide range of wavelengths that consistency amongdifferent products remains a problem. Nevertheless,the well-controlled emissions suggest that LEDs canprovide better accuracy and consistency in interpret-ing the fluorescence response to a LWUV source, aslong as an LED near 365 nm is used.

Fluorescence Colors from Different Defect Centers.3D fluorescence spectra provide an excellent oppor-tunity to examine fluorescence produced by individ-ual defects as well as the contributions of multipledefects. By directly depicting the relationship be-tween UV excitation and fluorescence emission,these spectra illustrate the emission resulting fromthe various optical centers. Fluorescence spectrafrom diamonds dominated by individual color cen-ters are relatively simple and consistent, as discussedfor each defect in the Results section. In most diamonds, multiple defect centers occur to-

gether. Even under pure 365 nm LWUV excitation, thefluorescence color will be a mixture of the fluorescencefrom different defect centers. The fluorescence mayalso have uneven zoning due to defect distributions.Visual observation alone is not an adequate basis forinterpreting a diamond’s fluorescence color with re-spect to the corresponding defect centers. The energyof the excitation source can have a profound effect onthe resulting fluorescence color and luminescencespectra, and it must be carefully considered.

Potential Effects of UV Light Sources on Fluores-cence Color and Intensity. Analysis clearly showsthat LWUV sources emit not only varying intensitiesand bandwidths of light at 365 nm, but also “extra”

peaks resulting from mercury lamps and leaking fil-ters. Our 3D fluorescence spectra demonstrate thatsmall changes in excitation wavelength, even from a“pure” LWUV emission, can significantly affect theintensity and possibly the color of the fluorescence.For example, the intensity of N3 luminescence (mea-sured at 439 nm) when excited by 400 nm excitationis approximately double that of the same emissionmeasured at 360 nm excitation (figure 6). The mix-ture of the emission peaks from the UV lamp will af-fect the apparent color and intensity of thefluorescence, limiting the effectiveness and consis-tency of visual observation.To illustrate the potential variations introduced

by “extra” excitation energy, figure 11A shows thefluorescence emission peaks from sample 15 (ex-tracted from the 3D fluorescence spectra of thissample containing the 480 nm band) at 365, 405,and 435 nm excitation energies. These are the threeemission peaks measured from the GIA LWUVlamp (365 nm being the strongest). The spectrawere processed to produce equivalent colors byconversion to equivalent CIE L*a*b* color valuesusing GRAMS AI software (including artifact re-moval, 2° viewing angle, and CIE D65 illumination;all spectral intensities were scaled up 30× to facili-tate color reproduction). The fluorescence peakgenerated by 365 nm excitation is centered at 520nm, producing a green color with a slightly yellowtint, whereas the fluorescence peaks caused by 405and 435 nm excitation energies are shifted up to~545 nm with a tail extending beyond 750 nm,adding an orange-red component to the yellowishgreen fluorescence. The strong yellow fluorescenceof this diamond under the conventional gemologi-cal UV lamp is a mixture of the three emission col-ors from these LW-UV excitation peaks. Under a“pure” 365 nm LED source, this diamond shows ayellowish green fluorescence. While it would beideal to illustrate this effect with photos, we couldnot achieve a long enough exposure to photographthe fluorescence.These multiple emission peaks from the hand-

held UV lamp can also affect the intensity of the flu-orescence color observed. Figure 11B shows thefluorescence emission peaks from sample 7 (ex-tracted from the 3D fluorescence spectra of its N3center) at the same 365, 405, and 435 nm excitationenergies used in the example above. Compared to365 nm excitation, the fluorescence color with 405nm excitation is almost twice as intense. The 435nm excitation gives a relatively small emission peak


centered at ~520 nm due to the presence of the H3center, resulting in a weak green color. “Extra” emis-sion from the conventional UV lamp at 405 nmcauses the diamond’s blue fluorescence to be moreintense than that from a “pure” 365 nm LED source.Such discrepancies contribute to problems with con-sistency and reproducibility of fluorescence observa-tions within the industry.

Fluorescence as a Tool for Identifying Treatment.Al-though we tested a limited number of samples, somedifferences in the fluorescence behavior of naturaland treated diamonds were observed. In diamondswith H3 or 480 nm band defects, 3D fluorescencespectra did not show significant differences betweenthe natural-color and treated samples. Yet treated di-amonds tended to show much more fluorescence


Figure 11. A comparison of diamond fluorescence color (samples 7 and 15) from a conventional UV lamp and asingle 365 nm excitation shows the effect of multiple emissions on the color and intensity of diamond fluores-cence. Colors were reproduced from spectra by conversion to equivalent CIE L*a*b* values with CIE D55 illumi-nation using Thermo GRAMS AI software. Excitation artifacts are marked in blue.

0

2

4

6

8

10

WAVELENGTH (nm)

FLU

OR

ESC

ENC

E IN

TEN

SITY

2nd orderexcitation

365 nmexcitation

0

2

4

6

8

10 405 nm

0

2

4

6

8

10

300 400 500 600 700 400 500 600 700

435 nm

0

2

4

6

8

10

300

435 nm

0

2

4

6

8

10 405 nm

0

2

4

6

8

10 365 nm

B. Sample 7A. Sample 15

from the (N-V)– center, partially overlapping with theband from the (N-V)0 center, whereas naturally col-ored stones showed a dominant (N-V)0 defect (again,see figure 10). Because the fluorescence from the (N-V)– center was much more intense in the treated di-amonds and shifted to longer wavelengths of >750nm, the fluorescence color from the treated dia-monds with both N-V centers was a more intense redcolor than in the untreated samples with only the (N-V)0 center, which produced an orange color. Whilethis trend for N-V centers after HPHT treatment iswell documented (e.g., Fisher and Spits, 2000) andalso proved true in this study, gemologists should notrely solely on the observation of orange or red fluo-rescence to ascertain diamond treatment.

CONCLUDING REMARKSTesting of diamonds with various primary defectcenters has shown that to define their fluorescence

characteristics, a UV source with consistent outputenergy is necessary. Traditional gemological UVlamps and light sources used in the diamond indus-try produce widely variable emissions, making itdifficult to achieve reproducible fluorescence obser -vations. LED light sources can provide narrow, wellconstrained UV emissions to produce more reliablediamond fluorescence reactions. This study characterizes the fluorescence gener-

ated by the most common defect centers in dia-mond. Changes in fluorescence relative toexcitation energy were carefully examined to deter-mine where fluorescence maxima occur for eachdefect, as well as the peak positions and bandshapes that can impact fluorescence colors and in-tensities. Our findings demonstrate the diamondindustry’s need for a standardized UV excitationsource, to provide consistent and reproducible de-terminations of fluorescence.


ABOUT THE AUTHORSDr. Luo ([email protected]) is supervisor of global metrology andDr. Breeding is a research scientist at GIA in Carlsbad.

ACKNOWLEDGMENTSThe authors thank GIA’s Ronnie Geurts, Wuyi Wang, Tom Moses,Jim Shigley, and Sally Eaton-Magaña, and GIA consultants MartinCooper and Chris Welbourn, for many helpful discussions. Assis-tance from David Nelson, John Innis, and Dylan Hand in collectionof spectroscopic data at GIA is also greatly appreciated.

Becquerel M.E. (1868) Sources de Lumière: Ses Causes et Ses Effets[Sources of Light: Its Causes and Effects]. Librairie de FirminDidot Frères, Paris, 431 pp.

Breeding C.M., Shigley J.E. (2009) The “type” classification systemof diamonds and its importance in gemology. G&G, Vol. 45,No. 2, pp. 96–111, http://dx.doi.org/10.5741/GEMS.45.2.96.

Collins A.T. (1982) Colour centers in diamond. The Journal ofGemmology, Vol. 18, No. 1, pp. 37–75.

——— (1974) Visible luminescence from diamond. Industrial Di-amond Review, Vol. 34, pp. 131–137.

Cotty W.F. (1956) Identification of diamonds by their fluorescence.The Journal of Gemmology, Vol. 5, No. 7, pp. 339–341.

Dyer H.B., Matthews I.G. (1958) The fluorescence of diamond. Pro-ceedings of the Royal Society of London: Series A, Mathemat-ical and Physical Sciences, Vol. 243, No. 1234, pp. 320–335,http://dx.doi.org/10.1098/rspa.1958.0002.

Eaton-Magaña S., Post J.E., Heaney P.J., Walters R.A., BreedingC.M., Butler J.E. (2007) Fluorescence spectra of colored dia-monds using a rapid, mobile spectrometer. G&G, Vol. 43, No.4, pp. 332–351, http://dx.doi.org/10.5741/GEMS.43.4.332.

Fisher D., Spits R.A. (2000) Spectroscopic evidence of GE POLHPHT-treated natural type IIa diamonds. G&G, Vol. 36, No. 1,pp. 42–49, http://dx.doi.org/10.5741/GEMS.36.1.42.

Fritsch E., Waychunas G.A. (1994) Gemstones. In M. Robbins, Ed.,Fluorescence: Gems and Minerals Under Ultraviolet Light,Geoscience Press Inc., Phoenix, AZ.

Holloway G. (2009) Blue fluorescence in diamond. The AustralianGemmologist, Vol. 23, No. 9, pp. 408–414.

Hoover D.B., Theisen A.F. (1993) Fluorescence excitation-emissionspectra of chromium-containing gems: An explanation for theeffectiveness of the crossed filter method. The Australian Gem-mologist, Vol. 18, No. 6, pp. 182–187.

Mani A. (1944) The fluorescence and absorption spectra of dia-mond in the visible region. Proceedings of the Indian Academyof Sciences A, Vol. 19, pp. 231–252.

Moses T.M., Reinitz I.M., Johnson M.L., King J.M., Shigley J.E.(1997) A contribution to understanding the effect of blue fluo-rescence on the appearance of diamonds. G&G, Vol. 33, No. 4,pp. 244–259, http://dx.doi.org/10.5741/GEMS.33.4.244.

Pearson G. (2011) Review of ultraviolet sources for gem fluores-cence and testing. The Journal of Gemmology, Vol. 32, No. 5-8, pp. 211–222.

Shigley J.E., Breeding C.M. (2013) Optical defects in diamond: Aquick reference chart. G&G, Vol. 49, No. 2, pp. 107–111,http://dx.doi.org/10.5741/GEMS.49. 107.

Shipley R.M. (1947) Notes on the abundance and color of fluores-cent diamonds. G&G, Vol. 5, No. 9, pp. 395–397.

Wild G.O., Biegel H. (1947) The fluorescence of diamonds. TheGemmologist, Vol. 16, No. 193, pp. 228–229.

Williams B. (2007) Technology update—ultraviolet light. GemMarket News, Vol. 26, No. 1, pp. 8–11.

REFERENCES

98 NEPHRITE JADE FROM VAL MALENCO, ITALY GEMS & GEMOLOGY SUMMER 2013

N ephrite jade is an almost monominer-alic rock, composed primarily of tremo-lite [Ca2Mg5Si8O22(OH)2] to actinolite

[Ca2(Mg,Fe)5Si8O22(OH)2] amphiboles (Leake et al.,1997). Although tremolite-actinolite is consideredthe predominant phase in nephrite jade, its specificweight percentage range is still debatable.

Major sources include the Kunlun Mountains inQinghai Province and the Xinjiang Uygur Au-tonomous Region of China; the East Sayan Moun-tains of Siberia; Chuncheon in South Korea; SouthWestland in the South Island of New Zealand; andCowell, Australia (Harlow and Sorensen, 2005; Liuet al., 2011a,b; Zhang et al., 2011).

A new deposit of gem-quality nephrite jade (figure1) was discovered at the beginning of the 2000s atAlpe Mastabia, located in the Val Malenco district inthe Sondrio province of northern Italy (figure 2). Mr.Pietro Nana first noticed an attractive green stone inthe discarded waste materials of an abandoned talcmine (figure 3) located at an altitude of 2,077 meters(Nichol and Geiss, 2005). The events leading to the

discovery of the Alpe Mastabia nephrite as well asthe geologic environment bear striking similaritiesto those reported by Dietrich and De Quervain (1968)for the better-known nephrite deposit at Scortaseo(Val Poschiavo, Switzerland), situated less than 20km away.

NEPHRITE JADE FROM VAL MALENCO,ITALY: REVIEW AND UPDATEIlaria Adamo and Rosangela Bocchio

FEATURE ARTICLES

Alpe Mastabia, in the Val Malenco district of northern Italy, has been a source of nephrite jade since theearly 2000s. Twenty-one samples from this locality were investigated by classical gemological methods;X-ray powder diffraction, combined with quantitative phase analysis; scanning electron microscopy incombination with energy-dispersive spectrometry; electron microprobe analysis; mass spectrometry;and mid-infrared spectroscopy. From a mineralogical standpoint, this jade consists mainly of tremoliteamphibole, with variable amounts of other constituents, especially calcite (up to approximately 30wt.%), but also pyroxene, apatite, and sulfide minerals. Its pale green color is related to the low ironcontent of the tremolite amphibole, whereas the other minerals are responsible for different colors (cal-cite for white, molybdenite and galena for gray). On the basis of minor and trace-element composition,we can classify this jade as dolomite-related nephrite (para-nephrite). Although new material could berecovered from this area, future production will probably be limited by access difficulties.

See end of article for About the Authors and Acknowledgments.GEMS & GEMOLOGY, Vol. 49, No. 2, pp. 98–106,http://dx.doi.org/10.5741/GEMS.49.2.98© 2013 Gemological Institute of America

Figure 1. Nephrite jade from Val Malenco is used in gemsand ornamental carvings, such as these bird statuettes(approximately 15 cm high). Courtesy of Pietro Nana.

This study aims to provide a review and updateof the nephrite jade from Val Malenco, by investigat-ing a suite of rough and cut gem-quality samples

using X-ray powder diffraction combined with quan-titative phase analysis based on the Rietveld method;scanning electron microscopy in combination withenergy-dispersive spectrometry (SEM-EDS); electronmicroprobe analysis in wavelength dispersion mode(EMPA-WDS); mass spectrometry; and mid-infrared(IR) spectroscopy.

GEOLOGIC SETTINGVal Malenco is an extremely interesting geological andmineralogical district (Adamo et al., 2009) situated inthe Rhetic Alps near the Italian-Swiss border betweenthe Southern Alps and the so-called “root zone” of theAlpine nappes. The main geological unit is an ultra-mafic body (the “Malenco unit”) that is one of thelargest ophiolitic masses of the Alps (figure 2). It is ex-posed in an area of about 130 km2 and consists of ser-pentinized peridotite with minor relicts of lherzoliteand harzburgite (Trommsdorff et al., 1993). The AlpeMastabia talc mine is situated in a narrow tectoniczone (Lanzada-Scermendone) at the southern marginof the Malenco unit (figure 2). About 300 meters awayis serpentinized rock, and the rocks around the talcmine are orthogneisses and schists (see box A) of thepre-Mesozoic crystalline basement, situated amongTriassic white calcitic to dolomitic marbles. The ori-gin of the talc deposit, as well as of tremolite andnephrite, is ascribed to metasomatic processes within

NEPHRITE JADE FROM VAL MALENCO, ITALY GEMS & GEMOLOGY SUMMER 2013 99

Switzerland

Italy

France

Austria

Alpe Mastabia,Val Malenco

ly

0 5 km

Malenco Unit

Alpe Mastabia

46˚ 15'N

Austroalpine nappes

N

Figure 2. Alpe Mastabia in Val Malenco, northernItaly, has been producing gem-quality nephrite jadesince the beginning of the 2000s. The inset showsthe area’s main geologic features. The AlpeMastabia talc/nephrite deposit is enclosed inschists, gneiss, and marbles.

Figure 3. Left: A view ofthe Alpe Mastabia talcmine with the nephritedeposit. Right: PietroNana stands near theentrance. Courtesy ofPietro Nana and Vin-cenzo De Michele.

the dolomitic marbles during the Alpine metamor-phism (Montrasio, 1984; Nichol and Giess, 2005).

HISTORY AND PRODUCTIONDuring the years of operation at the Alpe Mastabiatalc mine, from 1964 to 1994, nephrite boulders asso-ciated with the talc were ignored or discarded aswaste (Andreis, 1970; De Michele et al., 2002; Nicholand Giess, 2005). The mine was abandoned, and en-trances to its horizontal tunnels and galleries thatonce led to the ore body have mostly caved in or beenbarricaded (again, see figure 3), making the deposit dif-ficult to access. In 1995, while examining the wastematerial outside the mine, Mr. Nana noticed someattractive nephrite boulders. Recognizing their gemo-logical value, he consigned rough samples to lapidaryworkshops in China and Idar-Oberstein, Germany.The production and marketing of nephrite jade fromAlpe Mastabia started at the beginning of the newmillennium, with about 25 tons produced since thediscovery. Production still flourishes due to the highquality of the finished jewelry pieces and other orna-mental objects.

MATERIALS AND METHODSWe examined 21 samples from the Val Malenco de-posit, consisting of 13 cut (3.33–25.34 ct; figure 4) andeight rough (0.35–2.50 ct) specimens. All 13 cut sam-

ples underwent standard gemological testing to de-termine their refractive index (RI), specific gravity(SG), and ultraviolet (UV) fluorescence.

X-ray powder diffraction measurements were car-ried out on six rough specimens to determine thejade’s mineralogical composition. Data were col-lected by means of a Panalytical X’Pert-PROMPDX’Celerator X-ray powder diffractometer, usingCuKα radiation (λ=1.518 Å) at a beam voltage of 40


Nappe: A large body or sheet of rock that has shiftedfar from its original position by thrust faulting duringcontinental collisions. Also known as an allochton.

Ultramafic (or ultrabasic): Describing igneous andmeta-igneous rocks with very low silica content (lessthan 45% SiO2), generally greater than 18% MgO, highFeO, and low potassium. Ultramafic rocks are usuallycomposed of greater than 90% mafic minerals, whichare dark and have high magnesium and iron contents.

Peridotite: Coarse-grained ultramafic rock consistingmainly of olivine (at least 40% by volume) and pyroxene(ortho-/clino-). Peridotites are distinguished according totheir different mineralogical composition. Dunite con-tains more than 90% olivine. Wherlite is mostly com-posed of olivine (40–90%), clinopyroxene, and a minoramount of orthopyroxene (<10%). Lherzolite containsolivine (40–90%) and approximately equal amounts of

clinopyroxene and orthopyroxene. Harzburgite containsolivine (40–90%), orthopyroxene, and small amounts ofclinopyroxene (<10%).

Orthogneiss: Rock derived from the metamorphism ofigneous rocks. Orthogneiss is distinguished from para -gneiss, which derives from sedimentary rocks.

Schist: Metamorphic rock having a foliated or platedstructure called schistosity, in which the flaky miner-als (micas) are visible to the eye.

Metasomatic: Referring to a process by which thechemical composition of a rock or portion of rock is al-tered in a pervasive manner. Metasomatism involvesthe introduction or removal of chemical componentsas a result of the rock’s interaction with aqueous solu-tions. During metasomatism, the rock remains in asolid state.

BOX A: GEOLOGICAL GLOSSARY

Figure 4. These cut nephrite jades from Val Malenco(3.33–25.34 ct) were investigated in this study. Photoby Monica Odoli.

kV and a current of 40 mA. X-ray powder diffractionpatterns were collected over the 9–80° range of thescattering angle 2θ, with steps of 0.02° 2θ and a counttime of 25 seconds per step. The phase identificationwas based on data from the PDF-2 database (Interna-tional Center for Diffraction Data, Newton Square,Pennsylvania). Quantitative phase analysis (box B)was performed with the Rietveld method using the

GSAS software package (Larson and Von Dreele,1994) to treat the experimental 2θ-profile.

The microstructural features of six rough sampleswere investigated using a Cambridge STEREOSCAN360 scanning electron microscope (SEM), with an ac-celeration current of 15 kV. Semi-quantitative chem-

ical analyses were performed using the electron mi-croscope’s EDS system (ISIS 300 Oxford).

We also performed quantitative chemical analy-ses in situ of the fibrous crystals constituting the fourrough nephrite samples previously analyzed with X-ray powder diffraction. We used a JEOL JXA-8200electron microprobe in wavelength-dispersive mode(EMPA-WDS) under the following conditions: 15 kVaccelerating voltage, 15 nA beam current, and acount time of 60 seconds on peaks and 30 seconds onthe background. The following standards were used:natural grossular (for Si and Ca), anorthite (Al), fay-alite (Fe), olivine (Mg), rhodonite (Mn), omphacite(Na), ilmenite (Ti), K-feldspar (K), and pure V and Crfor those elements. The raw data were corrected formatrix effects using a conventional ΦρZ routine inthe JEOL software package.

The trace-element composition of the same fi-brous crystals in four rough samples was determinedby laser ablation–inductively coupled plasma–massspectroscopy (LA-ICP-MS). The instrument con-sisted of a Quantel Brilliant 266 nm Nd:YAG lasercoupled to a Perkin Elmer DRCe quadrupole ICP-MS. The spot size was 40 µm, using NIST SRM 610glass as an external standard and Ca as an internalstandard, as analyzed by microprobe. Precision andaccuracy estimated on the basaltic glass standardBCR2 were better than 10%.

Additional information was derived from hydro-gen isotope composition, obtained through multipleanalyses of a few milligrams of selected tremolite


Quantitative phase analysis (QPA) is used to deter-mine the concentration of various phases present in amixture after the identity of every phase has been es-tablished (qualitative phase analysis). Powder diffrac-tion is a direct method to identify and quantify phaseson the basis of their unique crystal structures(Pecharsky and Zavalij, 2003; Dinnebier and Billinge,2008).

Among existing QPA methods, the Rietveld (1969)technique appears to be one of the fastest and most reli-able. The foundation of the Rietveld method is that thedifference between the measured and calculated wholepowder diffraction profile should be close to zero bymeans of the following minimized function (Pecharskyand Zavalij, 2003):

where Y1obs is the observed and Y

1calc is the calculated in-

tensity of a point i of the powder diffraction pattern, andwi is the weight assigned to the ith data point.

The entire calculated powder diffraction pattern isbased on simultaneously refined models of the crystalstructures, diffraction optics effects, instrumental factors,and other specimen features. Rietveld refinement of multi-phase samples can generate a relatively accurate QPA, be-cause the Rietveld scale factors determined during the re-finements for every phase in the mixture are proportionalto the weight of the corresponding phases (Pecharsky andZavalij, 2003; Dinnebier and Billinge, 2008).

BOX B: QUANTITATIVE PHASE ANALYSIS

In Brief• Nephrite jade is an almost monomineralic rock, composed mainly of tremolite to actinolite amphiboles.

• The nephrite deposit at Alpe Mastabia, located in northern Italy’s Val Malenco district, has been producing nephrite jade since the beginning of the 2000s.

• The nephrite from Val Malenco is associated with dolomitic marbles (para-nephrite).

• This jade’s pale green color is due to the low concentration of iron, although other minerals (i.e., calcite, molybdenite, and galena) can also influence the color.

fibers by mass spectrometry following standard pro-cedures (Vennemann and O’Neil, 1993).

Mid-infrared absorption spectroscopy (4000–600cm–1) was carried out on four rough specimens usinga Nicolet Nexus Fourier-transform infrared (FTIR)spectrometer, operating in transmission mode withKBr pellets, at a resolution of 4 cm–1 and 200 scans persample.

RESULTSGemological Properties. The gemological propertiesof the 13 cut jades from Val Malenco are listed intable 1.The color of both the polished and rough sam-ples ranged from a common white and white-greento a rarer yellowish green and green (figure 4). Tworough samples had a blackish gray color (similar tothe bracelet’s color in figure 11). The RI was constant,while SG ranged from 2.74 to 2.96, with the lowervalues in the whitest samples. The SG values of thetwo blackish gray rough samples were 2.80 and 2.86.All the stones were opaque and inert to long- andshort-wave UV radiation. Irregular striped or spottedcolor zoning was observed in nearly every sample.

X-ray Powder Diffraction Data. Quantitative phaseanalysis based on XRPD data showed that five spec-imens consisted mainly of tremolite amphibole, withvarious amounts of other minerals, especially calcite.This mineral was generally less than 5 wt.%, thoughexceptional values of about 25–30 wt.% were foundin the two most whitish samples (table 2; figure 5).

Microstructure. The nephrite jade from Val Malencoshowed a micro- to crypto-crystalline texture thatconsisted of a dense intergrowth of fine (about 10–20μm long) randomly oriented bundles of tremolite


Figure 5.Based on Rietveld refinement of the X-raypowder diffraction pattern (9–80° 2θ-angle range) ofthe white nephrite sample 4C, the main constituentphases are about 70 wt.% tremolite and 30 wt.% cal-cite (peak positions marked in black and red, respec-tively). The lower pattern represents the residualbetween the calculated and experimental curves.

INTE

NSI

TY (

a.u.

)

QUANTITATIVE PHASE ANALYSIS

0.5

80.0

0.5

1.0

0.0

70.060.050.040.030.020.010.0

1.5

2θ (degrees)

TABLE 2. Mineralogical composition (wt.%) of thesix rough nephrite jade samples from Val Malenco.

Sample

Color

Tremolite

Calcite

4S

Green

100

0

6A

Green

99

1

6B

White-green

97

3

13

White-green

95

5

12

White

76

24

4C

White

70

30

TABLE 1. Gemological properties of the 13 cut nephrite jade samples from Val Malenco, Italy, investigated inthis study.

A

Whitishgreen

Opaque

1.60

2.95

6.5

Inert

B

Greenishwhite

Opaque

1.60

2.89

6.5

Inert

C

White-green

Opaque

1.60

2.89

6.5

Inert

D

Greenishwhite

Opaque

1.60

2.89

6.5

Inert

E

Greenishwhite

Opaque

1.60

2.96

6.5

Inert

F

Whitishgreen

Opaque

1.60

2.90

6.5

Inert

G

Greenishwhite

Opaque

1.60

2.86

6.5

Inert

H

White

Opaque

1.60

2.77

6.5

Inert

I

White

Opaque

1.60

2.74

6.5

Inert

L

Greenishwhite

Opaque

1.60

2.85

6.5

Inert

M

Yellowishgreen

Opaque

1.60

2.96

6.5

Inert

N

Yellowishgreen

Opaque

1.60

2.96

6.5

Inert

O

Green

Opaque

1.60

2.96

6.5

Inert

Color

Diaphaneity

Refractiveindexa

Specificgravity

Mohshardness

UVfluorescence

aMeasured by the distant vision method

fibers (figure 6). Other minerals were identified bySEM-EDS as calcite, diopside, apatite, and opaqueminerals (molybdenum, iron, lead, and zinc sulfides;see figure 7). Calcite was widespread in almost all

samples, whereas the other minerals were rarer. Inparticular, molybdenite and galena were more concen-trated in the blackish gray nephrite samples. Theseminerals were distributed unevenly in nephrite.

Chemical Composition. The chemical compositionof the fibrous crystals in the jade is reported for foursamples in table 3.

Chemical analyses of the fibrous mineral showeda composition close to that of tremolite amphibole,Ca2Mg5Si8O22(OH)2, according to the classification ofLeake et al. (1997), with a low concentration of mosttrace elements. All elements of the first transition se-ries (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn), as wellas the alkaline earth metals (Sr, Ba), and alkaline met-als (K, Rb, Cs) were always less than 0.1 wt.%, withthe lone exception of Na, ranging from 0.14 to 0.20wt.% as Na2O. Among the chromophore ions, ironwas the most abundant, with contents ranging from527 to 670 ppm (as Fe), followed by vanadium atabout 200 ppm (as V); chromium was much lower,with concentration ≤4 ppm (as Cr; table 3).

In terms of stable isotopic composition, the


Figure 8. The IR spectrum of the white nephrite sam-ple 4C shows absorption bands of tremolite (labeledT) and calcite (C).

WAVENUMBERS (cm-1)

AB

SOR

BA

NC

E

IR SPECTRUM

0.1

3000 2000 1000

0.4

0.5

0.6

0.7

1.0

3674T0.3

0.3

0.8

0.9

2513C

1799C

1423C

1108T

1067T

1000T

949T

949T

876C

758C

686T712C

Figure 7. SEM photos show the mineralogical compo-sition of the blackish gray (top) and white specimens(bottom). Tremolite is labeled T, calcite C, galena G,and molybdenite M.

Figure 6. Nephrite jade from Val Malenco is characterized by a finely fibrous texture, as shown in these SEM photos.

nephrite samples had a hydrogen isotopic meanvalue (δD) of –113± 4.8‰.

Mid-Infrared Spectroscopy. The samples’ mid-IR ab-sorption spectra, collected in transmission modewith KBr pellets (figure 8), were characterized bybands at 3674, 1108, 1067, 1000, 949, 922, 758, and688 cm–1, typical of tremolite (Hawthorne and DellaVentura, 2007). The whitest samples (12 and 4C) alsocontained the absorption features of calcite (2513,1799, 1423, 876, and 712 cm–1; Farmer, 1974).

DISCUSSIONThe various samples from Val Malenco exhibited RIvalues typical for nephrite jade (O’Donoghue, 2006).Their SG values, which showed variation with thecolor of the stones, were in agreement with those com-monly reported for this jade (SG=2.9–3.1; O’Donoghue,2006), except for the lower values in the two whitesamples (2.77 and 2.74, respectively; see H and I, table1). These SG values are compatible with a significantamount of calcite, whose SG (2.70 ± 0.01) is lower thanthat of tremolite. The Mohs hardness of 6.5 and thefinely felted fibrous texture are typical of nephrite fromlocalities worldwide (O’Donoghue, 2006).

The fine fibers of tremolite amphibole occurred to-gether with other unevenly distributed constituents.Calcite was the most abundant, although its con-tent varied from 0 to about 30 wt.%; pyroxene, ap-atite, and sulfide minerals were rarer. The variableamount of calcite corresponded with a white hue(figure 9), while molybdenite and galena were re-sponsible for the gray and black hues.

Chemical analysis of the tremolite fibers revealeda low abundance of minor and trace elements, with

iron as the most abundant chromophore ion. Yet itscontent shows comparable values in the various sam-ple colors from white to green (again, see figure 9). Thissuggests that the occurrence of other mineral phases(e.g., calcite) could influence the jade’s color variation.

Nephrite’s minor and trace-element chemicalcomposition plays an important role in tracing its ge-ologic origin. It is used to distinguish nephrite asso-ciated with dolomitic marbles (dolomite-related


TABLE 3. Average chemical composition of tremoliteamphibole in the nephrite jade from Val Malenco.

4S

59.410.010.260.030.01

23.1413.220.140.04

________96.26

0.001

8.1270.0010.0410.0030.0014.7191.9370.0380.007

1.2421.0

2152.10

81.2584

0.190.46

52.76.880.720.14

6A

59.870.020.04bdlb

0.0123.0113.160.150.04

________96.31

0.000

8.1760.0020.007bdl

0.0014.6841.9260.0390.007

1.4212.2

2712.47

80.7527

0.190.57

42.07.210.680.18

6B

59.600.020.290.010.01

23.1213.120.180.05

________96.39

0.000

8.1370.0020.0460.0010.0014.7051.9190.0470.008

1.3818.7

2934.20

84.5572

0.290.81

51.56.460.930.39

4C

58.980.020.480.080.02

22.8913.420.200.04

________96.12

0.002

8.0930.0020.0770.0090.0024.6811.9720.0530.008

1.1619.2

2202.20

87.8670

0.190.66

38.95.340.230.66

Sample

Oxides (wt.%)SiO2

TiO2

Al2O3

FeOMnOMgOCaONa2OK2O

Total

Fe/(Fe+Mg)

Ions per 23 oxygensSiTiAlFeMnMgCaNaK

Element (ppm) ScTiVCrMnFeCoNiZnSrYZr

Electron microprobe analysesa

LA-ICP-MS analysesc

a Ten points per sample were analyzed. FeO is the total iron. Cr is below detection limit in all samples.

b Abbreviation: bdl = below detection limit (0.01 wt.%).c Five points per sample were analyzed.

Figure 9. Calcite contents obtained by X-ray powderdiffraction analyses (see table 2) are shown for sixnephrite jade samples.

CALCITE CONTENT

SAMPLES

CA

LCIT

E (w

t. %

)

White-green

GreenGreen White-green

WhiteWhite

0

10

20

30

nephrite or para-nephrite) from that associated withserpentinite rock (serpentinite-related nephrite orortho-nephrite); see, for instance, Nichol (2000) andSiqin et al. (2012). In particular, various authors (e.g.,Siqin et al.) have shown that serpentine- anddolomite-related nephrite minerals can be separatedon the basis of their Fe/(Fe+Mg) ratio (0.064–0.118 and0.001–0.074, respectively) and their concentrations ofCr, Co, and Ni, which are higher in nephrite associ-ated with serpentinite. Based on the very lowFe/(Fe+Mg) ratio (always <0.002), as well as the lowcontents of Co (0.19–0.29 ppm), Cr (2.10–4.20 ppm),and Ni (0.46–0.81 ppm) found in the nephrite jadefrom Val Malenco (table 3 and figure 10), we can clas-sify this material as dolomite-related nephrite or para-nephrite.

The possible formation process for this type ofnephrite deposit is commonly ascribed to a metaso-matic reaction involving dolomite replacement by sili-cic fluids (Harlow and Sorensen, 2005). This isconsistent with the reaction proposed by Nichol andGiess (2005) for nephrite from Val Malenco, whichproduces excess calcite as isolated grains or aggregates:

5CaMg(CO3)2 + 8SiO2 + H2O = Ca2Mg5Si8O22(OH)2 + 3CaCO3 (dolomite) (silica) (tremolite) (calcite)

Yet the occurrence of diopside grains as rare relictswithin tremolite also suggests a second stage of for-mation involving the intermediate formation of diop-side from dolomite, subsequently replaced bytremolite. In any case, the formation of the AlpeMastabia deposit in Val Malenco implies an intensefluid-rock reaction by hydrothermal solutions, perco-lating at the contact between the dolomitic marbles

and the enclosing schists (Nichol and Giess, 2005).The very low δD-depleted value determined on thisnephrite also suggests a possible contamination of thehydrothermal fluid with water of meteoric origin (Yuiand Kwon, 2002; Harlow and Sorensen, 2005).

CONCLUSIONSNephrite jade from Val Malenco, northern Italy, en-tered the market at the beginning of the 2000s. Sincethe discovery of nephrite there in 1995, the deposithas produced about 25 tons of gem-quality rough,


CR VS. CO AND NI

Cr Cr

10

20

30

0

40

50

10 20 30 40 500 10 20 30 40 500

Co

500

0

1000

Ni

Serpentinite-RelatedNephrite

Dolomite-RelatedNephrite

Serpentinite-RelatedNephrite

Dolomite-RelatedNephrite

nephrite fromVal Malenco, Italy nephrite from

Val Malenco, Italy

Figure 10. Chromiumversus cobalt andnickel plots of the Ital-ian nephrite jade (greentriangles) are comparedwith nephrite datafrom Siqin et al. (2012).

Figure 11. These necklaces (top) and bracelet (bot-tom) consisting of approximately 10 mm diameterspheres are fashioned from nephrite jade from ValMalenco. Photos by Pietro Nana.

carved into ornamental objects or fashioned into jew-elry (figure 11). This study, performed on both cut andrough specimens, shows that nephrite jade from ValMalenco is composed of tremolite amphibole. It con-tains a low concentration of iron as a chromophore,in agreement with its pale green color. Variableamounts of other constituents also influence the

color: Calcite is responsible for the rather commonwhite hue, while molybdenite and galena cause theblack and gray colors. The nephrite’s compact mi-crostructure and soft color make it an attractive gemmaterial. Although new finds could be limited by ac-cess difficulties, the geologic features of the depositsuggest significant potential for further production.


ABOUT THE AUTHORSDr. Adamo ([email protected]) is junior researcher, and Dr. Boc-chio is professor of mineralogy, in the Earth Sciences departmentof the Università degli Studi di Milano, Italy.

ACKNOWLEDGMENTSThe authors thank Mr. Pietro Nana (Sondrio, Italy) for providingsamples and useful information about the material investigated inthis study. We also thank Mr. Andrea Risplendente (Universitàdegli Studi di Milano) for assistance with microprobe analyses;

Dr. Alberto Zanetti (CNR-IGG, Pavia) for assistance with LA-ICP-MS measurements; Dr. Valeria Diella and Mr. Agostino Rizzi(CNR-IDPA, Milan) for SEM-EDS analyses; and Dr. Monica Dapi-aggi (Università degli Studi di Milano) for collaboration during theX-ray powder diffraction data collection and analysis. The au-thors are also indebted to Dr. Luigi Dallai (CNR-IGG, Stable Iso-topes Laboratory, Pisa) for hydrogen isotope measurement. Dr.Loredana Prosperi (Istituto Gemmologico Italiano, Milan) andMrs. Nerina Saggiomo (Milan) are acknowledged for collabora-tion during this research.

Adamo I., Bocchio R., Diella V., Pavese A., Vignola P., Prosperi L.,Palanza V. (2009) Demantoid from Val Malenco, Italy: Reviewand update. G&G, Vol. 45, No. 4, pp. 280–287, http://dx.doi.org/10.5741/GEMS.45.4.280.

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Leake B.E., Woolley A.R., Arps C.E.S., Birch W.D., Gilbert M.C.,Grice J.D., Hawthorne F.C., Kato A., Kisch H.J., KrivovichevV.G., Linthouut K., Laird J., Mandarino J.A., Maresch W.V.,Nickel E.H., Rock N.M.S., Schumacher J.C., Smith D.C.,Stephenson N.C.N., Ungaretti L., Whittaker E.J.W., Youzhi G.(1997) Nomenclature of amphiboles: Report of the Subcommit-tee on Amphiboles of the International Mineralogical Associ-ation, Commission on New Minerals and Mineral Names.American Mineralogist, Vol. 82, No. 9/10, pp. 1019–1037,http://dx.doi.org/10.1180/minmag.1997.061.405.13.

Liu Y., Deng J., Shi G., Sun X, Yang L. (2011a) Geochemistry andpetrogenesis of placer nephrite from Hetian, Xinjiang, North-west China. Ore Geology Review, Vol. 41, No. 1, pp. 122–132,

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Yang L., Sun X. (2011b) Geochemistry and petrology ofnephrite from Alamas, Xinjiang, China. Journal of AsianEarth Sciences, Vol. 42, No. 3, pp. 440–451, http://dx.doi.org/10.1016/j.jseaes.2011.05.012.

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REFERENCES

NOTES & NEW TECHNIQUES GEMS & GEMOLOGY SUMMER 2013 107

Despite the commercial value of natural-color di-amonds, distinguishing them from treated dia-

monds remains a significant identification challenge.While some diagnostic visual features exist (inclu-sions, color or growth zoning, and absorption bandsseen with a spectroscope), the separation of naturalfrom synthetic or treated diamonds is not alwayspossible using standard gemological methods. Insuch cases, advanced spectroscopic analysis at a pro-fessional gem-testing laboratory is required. Imagingof luminescence distribution patterns is also a help-ful tool for recognizing synthetic diamonds (Mar-tineau et al., 2004; Shigley et al., 2004).In a laboratory setting, the identification of dia-

monds is based mainly on the detection of tiny im-perfections in the atomic lattice. These “defectcenters” may include foreign impurity atoms (typi-cally nitrogen, and occasionally boron or hydrogen);carbon atom vacancies in the lattice (either single orclusters of neighboring vacancies); carbon atoms po-sitioned in between normal lattice locations (intersti-tials); and dislocations where planes of carbon atomsare offset from one another due to plastic deforma-tion. Not all of these lattice imperfections create spec-troscopic features, but several do so by allowing the

diamond to absorb particular energies of incidentlight or radiation. Defects can occur randomly or inparticular locations within the lattice. Diamonds cancontain more than one type of defect, and in naturaldiamonds, defects can be altered over geologic timein the earth or by exposure to heat or radiation duringcolor treatment.So-called optical defects (or optical centers) cause

absorption in the visible or near-visible portions of theelectromagnetic spectrum, often producing coloration(e.g., figure 1). Luminescence reactions result whendefects absorb higher-energy incident radiation andthen reemit lower-energy radiation as visible light.Optical defects occur in very low concentrations inall diamonds, and their presence can be detected usingspectroscopic techniques. A theoretically “pure andperfect” diamond containing no such defects wouldappear colorless.

OPTICAL DEFECTS IN DIAMOND: A QUICK REFERENCE CHARTJames E. Shigley and Christopher M. Breeding

NOTES & NEW TECHNIQUES

Gem diamonds owe much of their value to theircolor, or lack thereof. Defects in the atomic struc-ture of diamond are responsible for this color andare important for the identification of color treat-ments. This article and its tables are intended asa quick reference for gemologists as they readabout various common diamond defects in thegemological literature.

See end of article for About the Authors.GEMS & GEMOLOGY, Vol. 49, No. 2, pp. 107–111,http://dx.doi.org/10.5741/GEMS.49.2.107© 2013 Gemological Institute of America

Figure 1. The red color of the graining in this Fancy reddiamond from Brazil is caused by absorption relatedto the 550 nm band. This band, the most commoncause of pink to red color in natural, untreated dia-monds, is thought to be the result of a defect createdby plastic deformation. Photo micrograph by Jian Xin(Jae) Liao; magnified 50×.

108 NOTES & NEW TECHNIQUES GEMS & GEMOLOGY SUMMER 2013

TABLE 1. Important optical defects in diamond and their effect on color and luminescence.

GR1: A defect with a pair of absorption lines at 740.9 nm (1.673 eV)and at 744.4 nm (1.665 eV) and associated bands. Thought toconsist of a vacancy in a neutral charge state (V0). Produced bynatural or artificial irradiation. UV, PL

Optical defect and spectroscopicLWUV DiamondView

Colormeans of detection

fluorescence luminescence(~365 nm lamp) (<220 nm source)

No effect No effect No effect

May contributeto a green color No effect No effect

No effect No effect

No effect No effect

May contributeto other colors No effect No effect

ND1: A defect with an absorption line at 393.6 nm (3.150 eV).Thought to consist of a vacancy in the negative charge state (V–).Produced by natural or artificial irradiation. UV

N3: An impurity and intrinsic defect with an absorption line at415.2 nm (2.985 eV) and associated bands. Thought to consist ofthree substitutional nitrogen atoms surrounding a vacancy (3N+V).Often occurs with the associated N2 (477.2 nm) and several otherrelated bands (465, 452, 435, and 423 nm) in “Cape” diamondspectra. All are naturally occurring. UV, PL, EPR

480 band: A naturally occurring optical defect of uncertain struc-ture (sometimes attributed to substitutional oxygen) in type Idiamonds with a broad absorption band centered at 480 nm(2.580 eV). UV

H4: An impurity and intrinsic defect with an absorption line at496.2 nm (2.498 eV). Thought to consist of four substitutionalnitrogen atoms surrounding two vacancies (4N+2V). Occurs naturally or can be pro duced by irradiation followed by annealing.UV, PL

H3: An impurity and intrinsic defect with an absorption line at503.2 nm (2.463 eV) and associated bands. Thought to consist oftwo substitutional nitrogen atoms separated by a vacancy in aneutral charge state (N-V-N)0. Occurs naturally or can be producedby irradiation followed by annealing or by high-pressure, high-temperature annealing. UV, PL

3H: A defect with an absorption line at 503.4 nm (2.462 eV).Thought to be related to interstitial carbon (I). Produced by naturalor artificial irradiation. UV, PL550 band: An optical center of uncertain structure with a broadabsorption band centered at 550 nm (2.250 eV). Thought to resultfrom plastic deformation of the lattice structure. Occurs naturally.UV

NV0: An impurity and intrinsic defect with an absorption line at575 nm (2.156 eV) and associated bands. Thought to consist of asingle substitutional nitrogen atom associated with a vacancy in aneutral charge state (NV0). Occurs naturally or can be produced byirradiation followed by annealing. PL, EPR, UV

595 band: An optical defect of uncertain structure with an absorptionband at 594.4 nm (2.086 eV). Thought to be related to nitrogen.Occurs naturally or can be produced by irradiation followed byannealing. UV

NV–: An impurity and intrinsic defect with an absorption line at637 nm (1.945 eV) and associated bands. Thought to consist of asingle substitutional nitrogen atom associated with a vacancy in anegative charge state (NV–). Occurs naturally or can be producedby irradiation followed by annealing or by high-pressure, high-temperature annealing. PL, EPR, UV


ColorOptical defect and spectroscopic

LWUV DiamondView

means of detectionfluorescence luminescence

(~365 nm lamp) (<220 nm source)

No effect No effect

Hydrogen: Defect(s) of uncertain structure with many relatedinfrared absorption lines, most notably at 3107 cm–1 (0.385 eV).Occurs naturally. This defect can also produce yellow and violetcolors. IR, UV

May contributeto a green color No effect No effect

H2: An impurity and intrinsic defect with an absorption line at986.3 nm (1.256 eV, 10125 cm–1) and associated bands. Thoughtto consist of two substitutional nitrogen atoms separated by avacancy in a negative charge state (N-V-N)–. Occurs naturally orcan be produced by irradiation followed by annealing or by high-pressure, high-temperature annealing. IR, PL


H1c: An impurity and intrinsic defect of uncertain structure withan infrared absorption line at 1934 nm (0.6408 eV, 5171 cm–1).Thought to be associated with nitrogen B centers. Occurs naturallyor can be produced by irradiation followed by annealing. IR


H1b: An impurity and intrinsic defect of uncertain structure withan infrared absorption line at 2024 nm (0.612 eV, 4941 cm–1).Thought to be associated with nitrogen A centers. Occurs naturallyor can be produced by irradiation followed by annealing. IR

Boron: A defect with a primary infrared absorption line at 2803cm–1 (0.348 eV) and associated lines, and a band extending intothe visible region. Thought to consist of single substitutional boronatoms. Occurs naturally. This defect produces red phos phores -cence. IR

Quenchesluminescence

Quenchesluminescence

A center: A defect with an infrared absorption band at 1282 cm–1

(0.159 eV). Thought to consist of two adjacent substitutionalnitrogen atoms (N-N). Occurs naturally. IR

No effect No effect

B center: A defect with an infrared absorption band at 1175 cm–1

(0.146 eV). Thought to consist of four adjacent substitutional nitrogenatoms surrounding a vacancy (4N+V). Occurs naturally. IR

No effect No effect

C center: A defect with an infrared absorption band at 1130 cm–1

(0.140 eV). Thought to consist of a single substitutional nitrogenatom (N). Occurs naturally or can be produced by high-pressure,high-temperature annealing of diamonds containing A or Bcenters. IR, UV, EPR


H1a: An impurity and intrinsic defect of uncertain structure withan infrared absorption line at 1450 cm–1 (0.180 eV). Thought to beassociated with interstitial nitrogen. Occurs naturally or can beproduced by irradiation followed by annealing. IR


Platelet: An impurity and intrinsic defect of uncertain structurewith an infrared absorption line at about 1360 cm–1 (0.169 eV).Thought to be associated with groups of interstitial carbon atoms.Occurs naturally. IR

No effect No effect

Vacancy cluster: A defect of uncertain structure with increasingabsorption toward the blue end of the spectrum. Thought to consistof groups of vacancies. Occurs naturally. UV

UV = Ultraviolet-visible absorption spectroscopyIR = Infrared absorption spectroscopy

PL = Photoluminescence spectroscopyEPR = Electron paramagnetic resonance spectroscopy

Phosphorescence Phosphorescence

As a quick reference for gemologists, table 1 liststhe most common lattice defects, including thosethat can create color and/or luminescence reactionsin diamond. The scientific name of the defect, as wellas the wavelength (or wavenumber) and electron volt(eV) positions of the main and associated spectralbands, are shown along with photos of representativediamonds. The most common spectroscopic tech-nique used to detect the defect center is indicated bya code shown in italics.

Some precautions should be kept in mind whenusing this table. Each lattice defect is known to pro-duce a particular diamond color or luminescence. Forinstance, the GR1 center produces green or blue-green color. But the reverse is not necessarily true—for example, not all green diamonds owe their colorto the GR1 center. In fact, there are several causes ofgreen color. In some cases, a diamond contains morethan one optical defect, and its color stems from acombination of defects. In other cases, a diamond’s

110 NOTES & NEW TECHNIQUES GEMS & GEMOLOGY SUMMER 2013

TABLE 2. Spectroscopic techniques for characterizing lattice defects in diamond.

Type ofspectroscopy

Absorption(transmission)

Absorption(transmission)

Luminescence

Luminescence

Luminescence

Resonanceabsorption ina changingmagneticfield

Typical scanrange

250–800 nm

400–11,000cm–1

100–2000cm–1 Ramanshift

350–1000 nm

400–700 nm

Advantages

Evaluation of color-causing defects;relativelyinexpensive

Determination ofdiamond type;relatively in -expensive; defectconcentrations canbe quantified bynormalization

Identification ofdiamond; analysisof internal strain

Detection ofHPHT treatment;characterization oflow-concentrationdefects; smallanalysis area allowsfor detailedinvestigation

Evaluation ofinternal structure;detection of defectscausingluminescence

Detection of verylow-concentrationdefects; evaluationof specific defectstructures andcharges

Disadvantages

Large samplesabsorb too muchlight, causingdetector saturation;difficulty quantifyingresults from facetedstones because ofthe uncertain pathlength of light travel

Large samplesabsorb too muchlight, causingdetector saturation

Expensive; yieldslittle informationregarding treatment;difficulty analyzingstrongly fluorescentsamples

Expensive; difficultyanalyzing stronglyfluorescent samples;variety of laserexcitations requiredto activate variousdefects; requirescarefully controlledcryogenic testtemperatures

Requires an electronbeam and a vacuum;provides littleinformation aboutcolor treatment

Very expensive;long sample runtimes; provides littleinformation aboutcolor treatment

Comments

Staple technique ingemologicallaboratories; can beperformed withscanning ordispersive detector

Staple technique ingemologicallaboratories

Typically used fordiamond vs. non-diamond identifica-tion (provides littleother information)

Lasers of variouswavelengths usedfor excitation (mostcommonly 325,488, 514, 532, and633 nm); requiredfor effectivetreatment detection

Rarely used, limiteddata obtainable

Typically used fordefect research

Technique

Ultraviolet/visible/near-infrared(UV-Vis-NIR)

Mid- to near-infrared(IR)

Raman

Photolumin escence(PL)

Cathodoluminescence(CL)

Electron-spin/paramagneticresonance (ESR, EPR)

Commonlydetected featuresand defects

ND1, N3, N2,H3, H4, 595nm, and GR1

A and Baggregatecenters, Ccenters, varioushydrogen-relateddefects, H1a,H1b, H1c, H2,and “ambercenters”

DiamondRaman line(1332 cm-1)

N3, 490.7 nm,H4, H3, NV0,NV–, GR1, H-and Ni-relateddefects

A band, B band,N3, H3, and H4

C centers, NVdefects

Testconditions

~77 Ktemperature

Roomtemperature

Roomtemperature

~77 Ktemperatureor lower

Roomtemperature

Roomtemperature

color may arise from absorption caused by one opti-cal center, while its luminescence may result fromanother optical center.Table 2 provides a comparison of the most com-

mon spectroscopic techniques for diamond charac-

terization. For further reading on color in diamond,the Additional Reading list serves as a referenceguide to access the much larger range of gemologicaland technical literature on diamond identification.


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Cunningham D. (2011) The Diamond Compendium. NAG Press,Robert Hale Ltd., London.

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Eaton-Magaña S., Post J.E., Heaney P.J., Walters R.A., BreedingC.M., Butler J.E. (2007) Fluorescence spectra of colored dia-monds using a rapid, mobile spectrometer. G&G, Vol. 43, No.4, pp. 332–351, http://dx.doi.org/10.5741/GEMS.43.4.332.

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Ed., The Nature of Diamonds. Cambridge University Press inassociation with the American Museum of Natural History,New York, pp. 23–47.

Hofer S.C. (1998) Collecting and Classifying Coloured Diamonds:An Illustrated Study of the Aurora Collection. Ashland Press,New York.

Martineau P.M., Lawson S.C., Taylor A.J., Quinn S.J., Evans D.J.F.,Crowder M.J. (2004) Identification of synthetic diamond grownusing chemical vapor deposition (CVD). G&G, Vol. 40, No. 1,pp. 2–25, http://dx.doi.org/10.5741/GEMS.40.1.2.

Shigley J.E., Breeding C.M., Shen A.H. (2004) An updated charton the characteristics of HPHT-grown synthetic diamonds.G&G, Vol. 40, No. 4, pp. 303–313, http://dx.doi.org/10.5741/GEMS.40.4.303.

Tappert R., Tappert M.C. (2011) Diamonds in Nature: A Guide toRough Diamonds. Springer, New York, pp. 45–68.

Zaitsev A.M. (2000) Vibronic spectra of impurity-related opticalcenters in diamond. Physical Review B, Vol. 61, No.19, pp.12909–12922, http://dx.doi.org/10.1103/PhysRevB.61.12909.

——— (2001) Lattice Defects in Diamonds: A Data Handbook.Springer-Verlag, Berlin.

ADDITIONAL READING

ABOUT THE AUTHORSDr. Shigley ([email protected]) is a distinguished research fellow,and Dr. Breeding is a research scientist, at GIA’s laboratory inCarlsbad, California.

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LAB NOTES GEMS & GEMOLOGY SUMMER 2013 113

Atypical Freshwater CULTUREDPEARLS with Damaged NacreRecently the East Coast laboratory re-ceived four baroque-shaped pearlsranging in size from 9.07 × 13.50 ×14.03 mm to 9.32 × 11.34 × 15.77 mmand weighing between 10.63 and 13.60ct. On each of the four samples, theoutermost surface nacre layers exhib-ited large holes and gaps, revealing oneor more distinct nacreous layers un-derneath (figure 1). These underlyingnacreous layers displayed good lusterand overlapping platelet surface struc-tures, and the large gaps between theinner and outermost nacre layers indi-cated that smaller pearls had been usedas nuclei during the culturing process.

Further gemological testing by en-ergy-dispersive X-ray fluorescence(EDXRF) and inductively coupled

plasma–mass spectrometry (ICP-MS)confirmed that both the outer andinner nacre layers originated from afreshwater environment. Some ofthese pearls contained widely varyingamounts of trace elements (i.e., Mnand Mg) between the outer and innerlayers, but previous studies havefound that uneven distribution oftrace elements can also occur in apearl’s cross section (R. Lu et al., “Op-erational considerations of EDXRF,LA-ICP-MS, and photoluminescencetechniques in the analysis of pearls,”Summer 2011 G&G, pp. 149–150).

Two did not show any distinct in-ternal demarcation when examinedwith X-radiography in various direc-tions (figure 2). This lack of a clear in-ternal boundary may be due to multipleculturing attempts using the same pearlas a nucleus, which can cause over-lapped internal structures and multipledistinct nacreous layers under the sur-face (figure 1, sample 3). In addition,structures typical of non-bead culturedpearls were observed in these micro X-radiographs, suggesting that freshwatercultured pearls were used as nuclei dur-ing the culturing process.

Finally, photographs of the X-rayfluorescence reactions of all fourpearls were taken in a dark environ-ment (figure 3). Various intensities ofgreen and yellowish green fluores-cence could be observed within eachnacreous layer, presumably due tovarying concentrations of manganesebetween layers and among the pearlsthemselves (H.A. Hanni et al., “X-rayluminescence, a valuable test in pearlidentification,” 2005 Journal of Gem-mology, 29, 5/6, pp. 325–329). Moreinterestingly, reddish fluorescencewas also observed around the dam-aged areas of the nacre in samples 3and 4. This was possibly caused byforeign material between the “nu-cleus-pearl” and the outer nacre lay-ers, which may also contribute to thelack of distinct demarcation observedin the cultured structure.

While similar types of pearls withintact outer nacre surfaces have beenreported on previously (E. Strack, “Chi-nese freshwater cultured pearls beadedwith baroque freshwater culturedpearls,” Fall 2011 G&G, pp. 244–245),the ambiguous internal structures, in-teresting X-ray fluorescence properties,

EditorsThomas M. Moses | Shane F. McClure

© 2013 Gemological Institute of America

GEMS & GEMOLOGY, Vol. 49, No. 2, pp. 113–118,http://dx.doi.org/10.5741/GEMS.49.2.113

Editors’ note: All items were written by staffmembers of GIA laboratories.

Figure 1. These four atypical freshwater cultured pearls with damaged nacre reveal one or more distinct nacreouslayers underneath. Left to right: samples 1–4.

and large gaps in the outer nacre layersof these four samples offer a rare viewof their internal physical structure andappearance, obtained free of destruc-tive testing.

Chunhui Zhou

DIAMONDCalcium Fluoride Coating Found On 13 “Fancy” PinksCoating gemstones to alter or im-prove their color is the oldest knownenhancement method. Early coatings,particularly on diamond, were easilydetected, often visible using a 10×loupe. But advances made after WorldWar II resulted in more durable coat-ings and films that were subtler andharder to detect.

A common coating was calciumfluoride (CaF2) doped with gold (Au)nanoparticles. CaF2 causes a broad ab-sorption band at about 520 nm, simi-lar to the band at about 550 nm thatlargely accounts for the pink color ofnatural diamonds.

Recently submitted to the EastCoast laboratory for identification andgrading was a group of 13 pink dia-monds (figure 4). The round brilliants

ranged from 0.42 to 0.50 ct and had aFancy pink to Fancy Intense pinkcolor. Figure 4 also shows the patchyappearance characteristic of coated di-amonds. Microscopic examinationusing reflected light revealed obviouscoating on the pavilion facets, withpatchy colorless areas where it hadbeen removed (figure 5).

The UV-visible spectra of all 13 di-amonds exhibited a broad band cen-tered at about 520 nm, not at 550 nmas expected. This band is responsiblefor the pink coloration, and the 520nm position identified the coating asfluoride.

This example demonstrates thattraditional treatments such as coatingare still prevalent in the trade, andgreat care must be taken to identifythem. Because coatings are not per-manent, all 13 diamonds were issuedidentification reports disclosing thetreatment.

Fish-Like InclusionIt is always a pleasant surprise to finda new and interesting inclusion duringroutine observation. But an inclusion

that reminds us of a particular shape,an effect known as pareidolia (Winter2007 Lab Notes, pp. 363–364), is a geo-logic wonder.

The New York laboratory recentlyreceived a natural yellow (graded asFancy yellow) “Cape” 0.51 ct rectangu-lar faceted diamond exhibiting such afeature. Examination of the stone re-vealed a series of table-reaching frac-tures and clouds that seemed to formthe outline and scale-like detail of a fish(figure 6). The inclusion is large in rela-tion to the stone, encompassing nearly75% of the table.

114 LAB NOTES GEMS & GEMOLOGY SUMMER 2013

Figure 3. X-ray fluorescence images of the four cultured pearls showingvarious degrees of green or yellowish green fluorescence between innerand outer layers. Atypical orangy red fluorescence is also visible betweenthe layers in samples 3 and 4.

Figure 4. These face-up images of0.45 ct and 0.5 ct pink round bril-liants are representative of the 13coated pink diamonds submitted.

Figure 2. X-radiographs show partial demarcation between the outer and inner structures of cultured pearls 1 and2, but fail to reveal any clear boundaries in samples 3 and 4.

Nearly all fractures in diamondresult from the interaction amongmultiple cleavage directions (TheMicro World of Diamonds, GemworldInternational, 2000, p. 97). While oftendetrimental to the value of a stone,this inclusion serves as a useful iden-tifier, and such findings help keep thestudy of gems enjoyable.

Martha Altobelli

A Large Irradiated Green-Yellow Artificially irradiated diamonds arecommon in the trade, and identifyingthem remains a challenge. The NewYork lab recently identified a large di-amond as artificially irradiated basedon careful spectroscopic analysis anda review of the lab’s database.

This 24.16 ct oval-cut diamond(20.47 × 14.00 × 10.72 mm) was colorgraded as Fancy Intense green-yellow

(figure 7). The color was distributedevenly throughout the stone, with nocolor zoning detected. It showedstrong yellow and blue fluorescence tolong-wave UV radiation, and moderateyellow fluorescence to short-wave UVradiation. This fluorescence reactionand absence of chalkiness are seen insome natural diamonds with a similarbodycolor. Absorption spectrum in themid-infrared region showed saturatedabsorptions in the one-phonon region,indicating a type Ia diamond with ahigh concentration of nitrogen. Alsorecorded were a moderate plateletpeak at 1368 cm–1 (approximately 2.1cm–1 intensity) and a weak absorptionat 1433 cm–1. No hydrogen-related ab-

sorption or H1b/H1c center in thenear-infrared region was recorded.Absorp tion spectrum of this diamondin the ultraviolet/visible/near-infrared(UV-Vis-NIR) region at liquid-nitrogentemperature (figure 8) showed a mod-erately strong absorption from the N3(415.2 nm) and H4 (496.0 nm) centers,as well as weak absorptions at 512.8,594.4, and 741.2 nm (GR1). Absence ofthe H3 optical center was confirmedby photoluminescence spectroscopy at


Figure 5. Photomicrographs of the diamonds from figure 4, taken with re-flected light at 80× and 100× magnification, reveal the coating applied tothe pavilion facets.

Figure 6. This pavilion view ofthe 4.76 × 4.30 × 2.75 mm Fancyyellow diamond displays the“fish” inclusion scene. The fishappears to be facing to the right.Magnified 40×.

Figure 7. This 24.16 ct oval-cut dia-mond (20.47 × 14.00 × 10.72 mm)was color graded as Fancy Intensegreen-yellow, and identified as ar-tificially irradiated and annealed.

Figure 8. After irradiation and annealing treatment, a significant amountof optical center H4 was introduced. This is mainly responsible for thecolor improvement from Fancy brownish greenish yellow to Fancy In-tense green-yellow. N3 absorptions in two spectra in this plot were nor-malized to the same intensity.

WAVELENGTH (nm)

UV-VIS-NIR SPECTRA

450 500 550 600 650 700 750

.1

.2

.3

.4

.5

.6

.7

AB

SOR

BAN

CE

Before treatment

After treatment

H4

741.2

(GR1)594.4

512.8

N3


liquid-nitrogen temperature with 488nm laser excitation. A fluorescenceimage collected using the Diamond-View showed a gradual change from apredominantly blue table region to amostly green upper pavilion and girdlearea. The spectral features observed inthis large diamond are rarely encoun-tered in natural diamonds, raising thepossibility of artificial irradiationtreatment.

A search of the GIA database founda very good match between this stoneand a previously tested diamond. Thetwo diamonds were identical in meas-urements and weight, as well as their in-frared absorption spectroscopic features,though the previous grade was Fancybrownish greenish yellow. This signifi-cant improvement in color appearanceis attributed to the relatively high con-centration of the H4 center produced bythe artificial irradiation/annealing treat-ment confirmed in this study.

Despite its suspicious spectroscopicfeatures, this irradiated diamondshowed some gemological features nor-mally observed in diamonds with sim-ilar natural color. This exampledemonstrates the value of careful spec-tral and gemological analysis, combinedwith a review of the GIA database, ingem identification.

Wuyi Wang, Paul Johnson, andEmiko Yazawa

Strong Color Zoning ReflectsComplex Growth EnvironmentA 2.08 ct emerald-cut diamond re-cently submitted to the Carlsbad lab-oratory received a color grade of FancyDark orangy brown. Its strong colorzoning, visible without magnification(figure 9), consisted of a dark orangybrown section with a few near-color-less bands and a near-colorless area.The orangy brown section showed nu-merous very small oriented reflectiveinclusions, visible in figure 9 only asdark clouds, that are typically associ-ated with type IaA diamonds coloredby 480 nm visible absorption bands.Both the near-colorless side and thecolorless bands displayed very few ori-ented reflective inclusions.

The diamond’s unusual fluores-cence under both long- and short-wave UV illumination can be seen infigures 10 and 11, respectively. Underlong-wave UV (handheld lamp) thenear-colorless section showed typicalblue fluorescence. The orangy brownsection displayed a yellowish fluores-cence, which is common in type IaAyellow diamonds. Under the higher-energy, shorter-wavelength UV exci-tation of the DiamondView, thedis tinction between the colors becameeven more pronounced, and the bluefluorescence of the near-colorlessbands was clearly visible within theyellowish green fluorescence of theorangy brown section. Yellow phos-phorescence, common in type IaA di-amonds colored by 480 nm visibleabsorption bands, was also observed inthe orangy brown area.

Infrared spectroscopy revealed atype Ia diamond with both A and B ag-gregates. When IR spectra were col-lected separately from thenear-colorless and orangy brown sec-tions, distinct differences were noted.The orangy brown section contained~33 ppm of A-aggregated nitrogen and~15 ppm of B-aggregated nitrogen,whereas the near-colorless sectionshowed significantly higher concen-trations: approximately 139 ppm of Aaggregates and 100 ppm of B aggre-gates. In addition to the higher overallnitrogen content, the near-colorlessportion contained a higher proportion

of B-aggregated nitrogen impurities. The unique zoning observed in this

diamond likely reflects changing con-ditions during growth. Variations in ni-trogen and possibly oxygen content inthe earth’s interior—480 nm defectsare reportedly related to oxygen impu-rities in diamond—could have pro-duced the noteworthy color andfluorescence zoning that reveal thecomplex growth history.

Troy Ardon

Very Large Rough Diamond Throughout history, the discovery ofvery large diamond rough has been arare occurrence. Not only is it un-likely to survive the journey fromdeep in the earth to the surface, butmodern extraction methods, includ-ing the use of crushers to break largerock, can reduce such specimens to

Figure 11. This DiamondViewimage of the color-zoned diamondshows an even more pronounceddistinction between the colors.

Figure 9. The strong color zoningin this Fancy Dark orangybrown diamond was visible at10× magnification.

Figure 10. Under long-wave UV il-lumination at 10× magnification,the diamond’s color zones showedblue and yellowish fluorescence.


smaller pieces. Therefore, the recentexamination of a 1,138 ct rough dia-mond (62.51 × 47.61 × 45.56 mm; fig-ure 12) provided a unique opportunityto document the largest single-crystalnatural diamond ever examined byGIA. While it is possible there havebeen larger unreported specimens, asearch of public sources (e.g., I. Bal-four, Famous Diamonds, 5th ed., An-tique Collectors Club, 2008) suggeststhis could be the second-largest roughdiamond in history—between the3,106 ct Cullinan and the 995 ct Ex-celsior, both of gem quality.

Known to be from the DemocraticRepublic of the Congo, this stone dis-played Raman spectroscopic featurescharacteristic of diamond. The sheersize presented a challenge with IR ab-sorption spectroscopy analysis, as itwas too large for the regular samplechamber, beam condenser, or DRIFTunits. Instead, we used an infrared mi-croscope with reflective mode and ob-tained a high-quality absorptionspectrum. The rough was identified asa natural type IaA diamond with veryhigh nitrogen concentration. We alsodetected a weak hydrogen-related ab-sorption peak at 3107 cm–1, a com-mon feature in natural diamond. Alsorecorded were strong absorptionbands at approximately 3300, 2920,1700, and 1550 cm–1, attributed to mi-cron and sub-micron inclusions. Pho-toluminescence spectra were recordedat liquid-nitrogen temperature with

various laser excitations. The mainemission features were broad bands at700 and 787 nm. The crystal also dis-played a very weak blue fluorescenceunder long- and short-wave ultravio-let radiation, another typical feature.

The irregular morphology of the1,138 ct rough was quite interesting, asdiamond usually occurs in octahedral ordodecahedral forms. But such a mor-phology is less likely to be maintainedas a large crystal forms. Numerous ran-domly shaped and distributed inclusionsmay have contributed to the irregularcrystal growth. These inclusions alsocaused the gray color appearance.

The specimen’s strong surface dis-solution provided a visual documentof its journey from deep in the earth.At the high temperatures in theearth’s interior, diamond can remainstable only under very high pressure.As the diamond was transported tothe surface, the decrease in pressurewould have dissolved the stone unlessit made the journey rapidly. The sur-face of the 1,138 ct crystal speaks tothe change that took place during itsjourney and represents the fine linebetween our experiencing this rareitem and never having known it at all.

John M. King and Wuyi Wang

Unusual Curved Color ZoningIn EMERALDWhile curved color zoning is typicallyassociated with melt-grown synthet-ics, particularly flame-fusion productssuch as synthetic corundum and syn-thetic spinel, an unusual naturalemerald with this feature was re-cently examined in the Carlsbad andBangkok laboratories. This 1.17 ctemerald was obtained for GIA’s per-manent reference collection (samplenumber 100305160993) at a streetmarket in Kabul, Afghanistan, for itsvery unusual inclusion scene. Thestone was represented as being ofAfghan (Panjsher) origin, but the in-ternal inclusions seemed to resemblethose of emeralds collected from theSwat Valley of Pakistan. Carefulchemical analysis by laser ablation–inductively coupled plasma–mass

spec trometry (LA-ICP-MS) was per-formed at the GIA lab in Bangkok.The chemical data showed a fairlyeven composition within the sampleexcept for chromium, which variedproportionately with the green colorzoning (from approximately 300 to9000 ppmw Cr). The chemical data ofthe unusual emerald were comparedto those of reference standards fromknown deposits, particularly Panjsherand the Swat Valley, to investigate itsprobable origin. The data showed aclose match only with the referenceemeralds from the Swat Valley, mak-ing that the most likely origin.

The gemological properties showedan RI of 1.589–1.597 and a visible spec-trum consistent with emerald. Thestone showed no reaction to a standard4-watt gemological UV light source.Microscopic examination revealed nu-merous inclusions of pyrite, carbon-ates, and reflective thin films orientedperpendicular to the optic axis (parallelto the length of the stone), a typical as-semblage of a natural emerald. Themost unusual observation about thisstone was a prominent green “S” shapecolor zone that ran down its length(figure 13). Emerald’s hexagonal struc-ture would ordinarily lead one to ex-pect planar or angular color zoningrelated to the crystal morphology. Thepresence of curving zones in a facetedemerald was an anomaly that neededfurther examination.

One possible explanation for the

Figure 12. This 1,138 ct single-crystal natural diamond (62.51 ×47.61 × 45.56 mm) is the largestever examined by GIA.

Figure 13. This 1.17 ct emerald,which hosted pyrite and carbon-ate crystals, displayed unusualcurved zoning.

PHOTO CREDITS:Chunhui Zhou—1, 2, 3; Jian Xin (Jae) Liao—4, 7; Paul Johnson—5; Martha Altobelli—6;Troy Ardon—9, 10, 11; Joshua Balduf—12;Sasithorn Engniwat—13; Nathan Renfro—14,16; Robison McMurtry—15

unusual zoning is that compressionalgeological forces caused shearing alongthe emerald crystal’s basal plane. Thiswas supported by the appearance ofpyrite grains, which looked as if single,brittle pyrite crystals had been shearedand slightly displaced parallel to thebasal plane of the beryl host (figure 14).This apparent lateral shearing move-ment throughout the emerald crystalcould have caused the pyrite grains toseparate into aligned tabular fragmentsoffset from each other and the berylhost. Also observed between the pyritegrains were planar optical irregulari-ties. These planes suggested localizedshear zones that would have signifi-cantly higher defect concentration,giving rise to the optical nonconfor-mity consistent with their location be-tween the tabular pyrite inclusions.Under cross-polarized illumination,we observed dense clusters of birefrin-gent crystals that were essentially in-visible under non-polarized lighting.The low relief of these dense inclu-sions suggested they were beryl inclu-sions within the beryl host, possibly aresult of partial recrystallizationcaused by dynamic environ mentalconditions.

Gemology is generally a non-de-structive, observational science, whichcan be limiting at times. Destructivetechniques could have revealed thecrystallographic orientation of thepyrite grains with respect to eachother and explained the stone’s un-usual structure. Because this was aunique sample, destructive testing

was not a practical approach. Whilethe exact cause of this unusual zoningremains unknown, it is certainly in-teresting and thought provoking.Thediscovery of such gems demonstratesthat there are complex geological con-ditions we do not yet understandwhich, when observed, invite furthergemological exploration.

Nathan Renfro, Vincent Pardieu,and Supharart Sangsawong

Rare Faceted NEPTUNITEAn 11.78 ct faceted “black” octagonalmodified step-cut stone was recentlypresented to the Carlsbad laboratoryfor identification (figure 15). Standardgemological testing revealed an RI of1.69–1.73 and a hydrostatic SG of3.19. Microscopic examination with afiber-optic light source showed thestone was actually a very dark orangyred. It was heavily included with frac-tures and platelets, as well as ran-domly oriented unidentified thinneedles evenly distributed throughoutthe gem (figure 16). These tests sug-gested neptunite, an identity con-firmed using Raman spectroscopy.

Neptunite commonly occurs inassociation with, and as a guest in-clusion in, the rare blue mineralbenitoite (E.J. Gübelin and J.I.Koivula, Photoatlas of Inclusions in

Gemstones, Vol. 1, ABC Edition,Zurich, 1986). Both minerals are Ti-bearing silicates. Benitoite may con-tain whitish inclusions of crossite(an amphibole) or natrolite (a zeo-lite), so it is possible that the thinneedles in this neptunite are com-posed of one of these metamorphicminerals. The main source of neptu-nite is San Benito, California, whereit is found along the walls of natro-lite veins in blueschist (B. Laurs etal., “Benitoite from the New IdriaDistrict, San Benito County, Califor-nia,” Fall 1997 G&G, pp. 166–187).The type locality for this material isthe Narsarsuk pegmatite in Green-land (O.V. Petersen and O. Johnsen,“Mineral species first describedfrom Greenland,” Canadian Miner-alogist Special Publication No. 8,2005, pp. 76–77). Neptunite crystalshave been found in sizes up to a fewinches, but they are rarely facetedbecause of their brittle nature andrelative softness (5–6 on the Mohsscale). The few crystals that arefaceted usually weigh less than 1 ct,making this large specimen of par-ticular interest. To the best of ourknowledge, this is the first facetedneptunite identified by GIA.

Amy Cooper and Tara Allen


Figure 16. The orangy red neptu-nite contained dense needles ofunknown composition. Field ofview: 1.72 mm.

Figure 15. This unusual 11.78 ctfaceted neptunite appeared to beblack but was actually a darkorangy red.

Figure 14. Arrays of tabular offsetpyrite fragments were seenthroughout this unusual emerald.Field of view: 0.86 mm.

COLORED STONES AND ORGANIC MATERIALS

Ancient tourmaline and beryl from Afghanistan. A largeprivate collection of beads and carvings from antique ex-cavations, assembled in the 1970s by a collector inAfghanistan, was recently examined. The pieces wereclaimed to be found near the ancient city of Bactra (mod-ern-day Balkh), 300 km northwest of Kabul near the borderwith Uzbekistan. Bactra was a center of the Bactrian civi-lization, which flourished from 2500 to 1500 Bc. The col-lection contains several thousand drilled beads, mostlyagate, carnelian, and rare blue chalcedony. The next mostabundant materials are turquoise—some as small as 1 mmin diameter—and lapis lazuli. Less common are garnet (twotypes of almandine), rock crystal, amethyst, serpentinite,and steatite, as well as organic materials identified asamber, pearl, and mother-of-pearl. Other very interestingfinds are treated rock crystal and milky quartz, both con-taining blue glass spots on their surfaces, similar to me-dieval sapphire imitations (Fall 2001 GNI, pp. 243–245).

The two most interesting pieces, a pink bird (figure 1)and a very pale blue bead (figure 2), were studied in detail.The bird had a light green bottom section, measured 13.9× 13.6 × 7.6 mm, and weighed 9.52 ct, with a refractiveindex close to 1.63. It was strongly pleochroic (pink andcolorless), and it was uniaxial negative in a conoscope. Inboth short- and long-wave UV light the center was inert,but a thin triangular zone of light blue fluorescence wasvisible near the surface. These tests confirmed the stone’sidentification as tourmaline. It was originally a “water-melon” tourmaline, pink with a green rim, but only asmall part of the green rim had been preserved.

The pale blue bead was set in a heavily corroded metal,probably bronze. The entire piece measured 20.7 × 12.3 ×6.7 mm and weighed 20.28 ct, with an RI close to 1.59. The

stone was weakly pleochroic (very light blue and colorless),inert in UV light, and uniaxial negative in a conoscope.These results indicated a very pale aquamarine. The iden-tification of both beads was confirmed by their Raman pat-terns, collected by A. Gilg (Technical University ofMunich).

Both beads are possibly among the oldest of their kind.Large and historically significant rubellites have been re-ported from the 14th and 16th centuries, and a single berylbead from Nubia has been dated back to Predynastic time(before 3200 Bc), but few details are known. The first beryllocality of significance was reportedly the Egyptian emeralddeposit exploited as early as the Ptolemaic era (after 332 Bc).

Both tourmaline and aquamarine are typical pegmatiteminerals. Gem-bearing pegmatites have been mined sincethe 1970s in the Nuristan province of eastern Afghanistanand northern Pakistan—the possible origin of both beads.

Jaroslav Hyršl ([email protected])Prague, Czech Republic

120 GEM NEWS INTERNATIONAL GEMS & GEMOLOGY SUMMER 2013

Contributing EditorsEmmanuel Fritsch, CNRS, Team 6502, Institut des Matériaux Jean Rouxel (IMN), University of Nantes, France ([email protected])Franck Notari, GGTL GemLab–GemTechLab, Geneva, Switzerland ([email protected])Kenneth Scarratt, GIA, Bangkok, Thailand ([email protected])

Figure 1: This 9.52 ct pink tourmaline is part of an ex-tensive private collection of ornaments claimed to befrom ancient Afghanistan. Photo by Jaroslav Hyršl.

© 2013 Gemological Institute of America

GEMS & GEMOLOGY, VOL. 49, NO. 2, pp. 120–124,http://dx.doi.org/10.5741/GEMS.49. 2.120

Editors’ note: Interested contributors should send information and illustra-tions to Justin Hunter at [email protected] or GIA, The RobertMouawad Campus, 5345 Armada Drive, Carlsbad, CA 92008.

Orangy pink coated “soft coral.” Dyeing white coral to im-itate popular colors such as red, orange, and pink is awidely known practice. But a bead strand examined at theGem Testing Laboratory in Jaipur, India, revealed a color-ing method unfamiliar to gemologists (figure 3).

The strand weighed approximately 380 ct and containedspherical beads ranging from 6 to 15 mm in diameter. Thesewere identified as coral belonging to the species Melithaeaocracea of the order Alcyonacea (e.g., M.c. Pederson, Gemand Ornamental Materials of Organic Origin, Elsevier But-terworth-Heinemann, Oxford, 2004, pp. 192–218). Their sur-face showed deep pores and dull luster. The presence ofpores was sufficient to identify the beads as soft coral, whichis also characterized by a spongy, brittle, rough appearance.

Although their identification was straightforward, thebeads’ appearance caused doubt regarding their color origin.When viewed under magnification (figure 4), distinct colorconcentrations were visible within the surface pores andcavities. The coloring agent was restricted to the surface,

producing an enamel-like appearance in the trenches whilethe ridges appeared white. This evidence suggested that thebeads were coated with paint rather than dyed.

Although the microscopic features were sufficient foridentification, further tests confirmed those findings.Under UV light, the beads displayed bright orange fluores-cence (more strongly under short-wave), a feature com-monly associated with pink-orange dyes. No typicalabsorption spectra were visible under a desk-model spec-troscope or recorded with a UV-Vis-NIR spectrometer. Thisis because the beads’ dull luster, opacity, and rough, unevensurfaces neither reflect light (in diffused reflectance mode)nor absorb it (in transmission mode). Weak and broad ab-sorption bands were displayed at approximately 540 and680 nm, and the presence of calcium carbonate (aragonite)was confirmed by Raman spectroscopy.

Such “soft coral” is commonly dyed red and the poresare filled with a polymer to enhance polish and luster. Butthis specimen’s color and luster were unusual. The lab alsoreceived similar coral strands in pink and black, suggestingthis dye method can produce a variety of colors.

Gagan Choudhary ([email protected])Gem Testing Laboratory, Jaipur, India

Strands of tiny akoya keshi pearls.How small can a pearl be?At the American Gem Trade Association show in Tucson,the Japanese Pearl Exporting co. presented some akoya keshipearls only 0.7–0.9 mm in diameter (figure 5). At this size, itis difficult to distinguish individual pearls when looking at astrand. According to the seller, the single strand shown infigure 5 contains more than 300,000 keshi pearls, whichwould take one person four years to drill and assemble.

Traditional tools are used to drill these tiny pearls. Athick wooden board is soaked overnight to soften it, andeach pearl is embedded in the board to keep it stable. A

GEM NEWS INTERNATIONAL GEMS & GEMOLOGY SUMMER 2013 121

Figure 2: This aquamarine bead, reported to be fromAfghanistan, weighs 20.28 ct and is likely one of theoldest of its kind. Photo by Jaroslav Hyršl.

Figure 4. Under magnification, distinct color con-centrations are visible within the pores and cavitiesof this “soft coral.” The apparent use of a coloringagent only on the surface, evidenced by the enamel-like appearance within the trenches and the white-ness of the ridges, suggests these beads were coated,not dyed. Photomicrograph by Gagan Choudhary;magnified 48×.

Figure 3. This string of orangy pink “soft coral” beads(6–15 mm in diameter) displayed a rough surface andlarge pores. Photo by Gagan Choudhary.

very sharp, thin drill is used to bore a hole in each pearl.By pulling a thread attached to the drill, the worker cankeep rotating the drill until it reaches the desired depth.

“Keshi,” the Japanese word for poppy seeds, form as by-products of the akoya culturing process. They account for lessthan 0.5% of all annual akoya production, which has dimin-ished in recent years. Akoya keshi pearls come in varioussizes, shapes, colors, and lusters. Strands are often paired withcolored stones such as ruby and sapphire (figure 6).

Tao HsuGIA, Carlsbad

Green kyanite. At the Riverpark Inn show in Tucson, gemdealer Tom Schneider (San Diego, california) exhibited aparcel of kyanite displaying an unusual saturated yellowishgreen color (figure 7). Mr. Schneider said he purchased sev-eral kilograms of the material in Arusha, Tanzania, itsstated country of origin. While greenish blue, blue, and or-ange kyanite from Tanzania have been previously docu-mented (Winter 2004 GNI, pp. 341–342; Summer 2009GNI, pp. 146–147), this would be the first vibrantly coloredyellowish green material from there. Yellowish green kyan-ite from Brazil has been previously reported (Winter 2001GNI, pp. 337–338), but it had a light color and lacked thestrong saturation of the material from Tanzania.

A cushion cabochon fashioned from one of the roughcrystals was examined in the carlsbad laboratory and

exhibited the following properties: an RI of 1.719–1.731,a hydrostatic SG of 3.70, and no reaction to short- orlong-wave UV radiation. These physical properties wereconsistent with those published for kyanite. This iden-tification was confirmed by Raman spectroscopy.

Microscopic examination revealed several transparentcrystals, fine particles, numerous fractures, and cleavages.Trapped in several cracks was an epigenetic reddish brownmineral residue. It is also notable that a small percentage ofthe rough crystals examined showed narrow blue color zones.

To determine the cause of the yellowish green color, wecollected a visible spectrum using a UV-Vis-NIR scanningspectrophotometer (figure 8). This revealed prominent fea-tures located in the visible region at 432 and 445 nm. Thesefeatures have been attributed to Fe3+ in kyanite (R.G. Burns,Mineralogical Applications of Crystal Field Theory, 2nd ed.,1993, cambridge University Press). LA-IcP-MS measure-ments collected on the cushion cabochon confirmed a highconcentration of iron—more than 20,400 ppmw, consistent


Figure 5. This strand contains more than 300,000akoya keshi pearls, each one only 0.7–0.9 mm in di-ameter. Photo by Eric Welch. Figure 7. These yellowish green kyanite rough crystals

range from 1.4 to 5.1 grams, while the cushion cabo-chon weighs 4.84 ct. Photo by Don Mengason.

Figure 6. These tiny akoya keshi pearl strands arepaired with ruby and sapphire. Photo by Eric Welch.

Figure 8. Visible spectroscopy revealed dominantabsorption features at 432 and 445 nm, attributedto Fe3+ and consistent with the very high levels ofiron measured in this yellowish green kyanite.

WAVELENGTH (nm)

VISIBLE SPECTRUM

400350 450 500 550 600 650 700 750 800

0

5

10

15

AB

SOR

PTIO

N C

OEF

FIC

IEN

T (c

m-1)

432 nm

445 nm

with the saturated yellowish green color. This new supply of vibrant yellowish green material

from Tanzania presents an inexpensive option for unusualornamental gem materials.

Nathan Renfro and Andy ShenGIA, Carlsbad

Banded mimetite. Mimetite is a member of the apatitegroup and a lead chloro-arsenate, known to collectors asone of the rarest faceted stones. Some yellow transparentspecimens weighing up to 1 ct are known from old findsin Tsumeb, Namibia. Small orange translucent stonesunder 0.5 ct have been faceted from chinese mimetite, anda new type of lapidary mimetite (figure 9), likely from Bo-livia but purchased in Tucson without a reported locality,was identified recently.

The cabochon measured 40.5 × 31.7 × 7.2 mm andweighed 177.75 ct, with a very high luster. Its lapidary workwas of low quality, but the stone had a very nice agate-likestructure, with alternating yellow-brown and dark brownlayers. It closely resembled two unusual ornamental stones:the colloidal variety of sphalerite (figure 10) known by theGerman name schalenblende, and the colloidal cassiteritevariety called “wood tin.” Schalenblende is known frommany localities worldwide, mainly Poland but also Bolivia,where it is very difficult to visually distinguish frommimetite. Wood tin is known to be from Bolivia and Mexico.

The RI of all three minerals is very high, over the refrac-tometer limit. Loose stones can be easily distinguished bytheir hardness and specific gravity, and the hardness ofmimetite and schalenblende is the same, about 3.5 on theMohs scale. Wood tin is much harder, about 6.5. The SG ofthe mimetite was 6.31, considerably higher than the 3.8–4.2of a typical schalenblende. The SG of wood tin can vary from5.2 to 6.6, likely depending on the presence of thin chal-cedony layers. Mimetite and wood tin are also inert in UVlight, while schalenblende is usually yellow in long-wave

UV. The mimetite was identified by powder X-ray diffractionby John Attard of San Diego, but its exact origin could notbe determined. Thin veins of mimetite deposited from hotsprings are known to have been mined from a deposit inLomitas, located in La Paz Department, Bolivia.

Jaroslav Hyršl

Turquoise-rock crystal composite.Recently examined wasa faceted rock crystal backed by a slice of turquoise—anobvious but unusual combination of gem materials. The21.58 ct oval measured 20.02 × 15.03 × 9.05 mm and waseasily identified as a composite due to its color and appear-ance. From the top, it appeared light greenish blue (figure11, left); from the sides, it exhibited a colorless top andbluish green slice at the base (figure 11, right).

Further tests confirmed the specimen was made of rockcrystal and turquoise, based on its colorless and greenishblue components. The colorless portion displayed an RI of1.543–1.552, with birefringence of 0.009, while the greenishblue layer displayed a vague shadow edge at around 1.61.Under magnification, the colorless portion was clean andfree of inclusions, while the greenish blue base showed somewhitish cloudy patches, consistent with those in turquoiseand similar materials. As expected, the junction plane con-tained numerous trapped, flattened gas bubbles withoutcolor. Under long- and short-wave UV light, a white to lightyellowish glow was visible only along the junction plane,indicative of glue. Under a desk-model spectroscope, thespecimen showed a weak absorption at about 430 nm.

FTIR spectra taken by orienting the colorless portion dis-played peaks at approximately 3595, 3480, 3380, 3305, and3198 cm–1—a pattern typically associated with natural rockcrystal (e.g., Summer 2011 GNI, pp. 146–147). Raman analy-sis of the greenish blue base using a 532 nm laser in the 200–2000 cm–1 region revealed a strong peak at about 1040 cm–1,with a number of weaker peaks at approximately 238, 334,427, 482, 554, 596, 645, and 810 cm–1. These peaks are con-sistent with those of turquoise in both the lab’s database andthe RRUFF database of Raman spectra. No polymer-related

GEM NEWS INTERNATIONAL GEMS & GEMOLOGY SUMMER 2013 123

Figure 10. The sphalerite variety schalenblende has char-acteristics similar to those of banded mimetite. Thisspecimen weighs 106.20 ct. Photo by Jaroslav Hyršl.

Figure 9. This mimetite cabochon, likely from Bolivia,weighs 177.75 ct and has an agate-like structure ofyellow-brown and dark brown layers. Photo byJaroslav Hyršl.

peaks were present. In addition, qualitative energy-disper-sive X-ray fluorescence (EDXRF) analysis revealed the pres-ence of Al, P, Fe, and cu, consistent with turquoise. Asmentioned, a desk-model spectroscope revealed a weak ab-sorption at around 430 nm, and the same was confirmedusing UV-Vis spectroscopy, which displayed a sharp peak atapproximately 429 nm (Fe3+) and a broad absorption at about680 nm (cu2+), suggesting natural rather than dyed color.

While analysis using both classical and spectroscopictechniques identified this as a composite of natural rock crys-tal and turquoise, the reason for its creation is still unclear.

Gagan Choudhary

SYNTHETICS AND SIMULANTS

Imitation Larimar. Pectolite is a mineral of the wollastonitegroup with the chemical formula Naca2Si3O8(OH). It has anRI of 1.599–1.628, with a typical spot RI reading of about1.60 and a specific gravity of 2.81. The light blue variety ofthis mineral, known by the trade name “Larimar,” has onlybeen reported from the Dominican Republic (R.E. Woodruffand E. Fritsch, “Blue pectolite from the Dominican Repub-lic,” Winter 1989 G&G, pp. 216–225; figure 1).

We recently acquired a 3.91 ct drop-shaped cabochon,purchased in India as a Larimar imitation, that consistedof a ceramic material (figure 12, left). According to the ven-dor, the material was manufactured in china. close mi-croscopic examination showed white gas bubbles and bluecolor concentration (figure 13).

The cabochon’s spot RI reading of 1.53 and SG of 1.87

were distinctly lower than the values for Larimar. Semi-quantitative EDXRF chemical analysis gave a compositionof 95% Al2O3 and 4% SiO2, with traces of SO3, K2O, caO,Sc2O3, cr2O3, Fe2O3, and Ga2O3. In contrast, the averagecomposition of pectolite consists of 54.23% SiO2,33.74% caO, 9.32% Na2O, and 2.71% H2O.

Although the imitation material does indeed resembleLarimar, standard gemological tests such as microscopy,RI, and SG should be sufficient to distinguish it.

Lore KiefertGübelin Gem Lab Ltd.Lucerne, Switzerland

Peter GroenenboomAEL Arnhem

Arnhem, Netherlands

ERRATA

1. The Spring 2013 “About the cover” on the mastheadpage should have listed the photographer as Jian Xin (Jae) Liao.

2. The Lab Notes figure 7 photo was by Paul Johnson.3. In the GNI entry on dumortierite-quartz rock, two

lines were omitted from the bottom left column on p. 60.The complete version is available in the Spring 2013 issueat www.gia.edu/gems-gemology.


Figure 12. This 3.91 ct ceramic imitation of Larimar(left) is shown with Larimar from the DominicanRepublic. Photo by Lore Kiefert.

Figure 13. Microscopic observation reveals darkblue color concentrations and whitish gas bubbles.Photomicrograph by Lore Kiefert; magnified 40×.

Figure 11. This 21.58 ctcomposite was found tohave a top section ofnatural rock crystaland a base of naturalturquoise. Photos byGagan Choudhary.

BOOK REVIEWS GEMS & GEMOLOGY SUMMER 2013 S1BOOK REVIEWS GEMS & GEMOLOGY 2013 S1

The Young Generation—Tom +Jutta MunsteinerBy Wilhem Lindemann, 225 pp.,illus., publ. by Arnoldsche ArtPublishers, Stuttgart, Germany,2012. US$85.00

With this remarkable bilingual vol-ume, Wilhem Lindemann presentsthe works of husband and wife Tomand Jutta Munsteiner, master gemcutters and jewelers. Second-genera-tion gem cutter Tom Munsteiner fol-lowed in his father’s footsteps.Beginning in the 1960s and continu-ing through the mid-1990s, BerndMunsteiner reinvented gemstonecutting with his unique edged, multi-faceted gem carvings. Working nearIdar-Oberstein, the mecca of theGerman lapidary and colored stonetrades, he cut an abundance of “redis-covered” gemstones from Brazil’spegmatites, particularly tourmalines,aquamarines, amethysts, quartzes,and topazes.

Tom and Jutta Munsteiner wereclassically trained as apprentices aftershowing early artistic promise.Today, they exhibit at venues such asthe Tucson, Las Vegas, and Baselshows. Visiting the couple’s booth,one can only be struck by thestrength and originality of their cre-ations. Whether gem carving orsculpture, each work exhibits a finecombination of jewelry and art.

In the first part of the book,Lindemann retraces the evolution oflapidary art, from late third millen-nium BC cylinder seals to contempo-rary art movements such asBauhaus. Tom Munsteiner’s influ-ences, dating as far back as theRomantic era, have inspired him toenvision the entire crystal as a land-scape, with its inclusions and flaws.

He rejects traditional gem cuts suchas the round brilliant, which focuseson the reflecting quality of a dia-mond and is far too complex forhuman sight. For this reason headopted a cutting style that is asym-metrical, inviting the viewer’s atten-tion inside the crystal rather than onits reflective qualities.

The next section takes the readeron an inspirational journey throughthe work of Tom Munsteiner, whosemost memorable creations include“Magic Eye,” “Ritmo,” and “Spirit ofNature.” The “Magic Eye” pieceshave a sphere carved into the back ofthe gems at the interface of their axesto produce reflections on the face.“Ritmo” features geometric notcheson the reverse side that re-create ran-dom asymmetrical imaginary struc-tures. Of particular interest to gemol-ogists is the “Spirit of Nature” seriesof gem carvings, which accentuatesthe inclusions in a wide range ofmaterials. Some of the most strikingpieces are an oligoclase with redhematite platelets, an elongatedaquamarine prism with a helicoidalinclusion running through the lengthof the gemstone, and rock crystalcarvings displaying phantom crystals.This section is one of the book’sstrongest.

The third part focuses on Jutta’sjewelry designs, which feature herhusband’s gem carvings. Her inspira-tion features sinuous curves, as evi-denced by the “Personalities” neck-piece series. The imposing “Jeanned’Arc” necklace shows a ridged, elon-gated rutilated quartz mounted on acustom-made snake chain.

The fourth part illustrates Tomand Jutta’s collaboration throughimages of their classic jewelry, suchas the “Twins” series of rings, each

featuring an original gemstone carv-ing paired with a diamond. Theyincorporated a proprietary round cutcalled “Spirit,” as well as the square“Context,” which resembles a mod-ern French cut.

The photos exhibit a precisionthat complements the Munsteiners’cutting style. The rendering of colorhas not been artificially enhanced,which is often a treacherous tempta-tion. Captions generally mention thecarat weight of the gemstones, whichis important since neither scale nordimension are indicated. Given theimpressive size of certain objects,this information helps the readerappreciate the quality and craftsman-ship involved. Numerous illustra-tions show the variation of cutting,within each series and from oneseries to another. The many photosserve to distinguish the couple’srespective pieces: Tom’s unique gemcarvings and Jutta’s minimalist jew-elry designed with a sharp, powerfulstyle.

The text speaks to the Mun -steiners’ inspiration, but alsodescribes how the gems were cut—ahelpful feature since some of thegems were cut from the back to createa sense of volume and depth. Withoutthose details, such techniques wouldbe difficult to comprehend.

This magnificent opus wouldhave benefited from the Mun -steiners’ original sketches, whichwould have made the volume livelierand more personal. Some basic tech-nical explanation of cut and lapidarywork, being the couple’s craft andexpertise, would have also providedsome foundation. But these criti-cisms are minor considering thequality of gemstones and illustra-tions presented.

S2 BOOK REVIEWS GEMS & GEMOLOGY SUMMER 2013S2 BOOK REVIEWS GEMS & GEMOLOGY 2012

The illuminating text and thestriking originality and craftsman-ship of the Mun steiners’ work makethis volume a real treat for students,gemologists, gem cutters, and jewelryenthusiasts. It offers an incomparableinsight into Europe’s contemporaryand cutting-edge creations

DELPHINE A. LEBLANCHoboken, New Jersey

Dictionary of Gemstones &JewelryBy Akira Chikayama, 652 pp., illus.,publ. by IMACBC Co., Tokyo, 2013,US$100.00

The late Akira Chikayama was anoted gemologist who considered theDictionary of Gemstones & Jewelryhis personal “world heritage.”Indeed, the very scope of this dictio-nary is impressive. Entries includegems, minerals, sources, synthetics,treatments, jewelry findings, toolsused in gem cutting and jewelrymaking, famous gemologists, scien-tists, mineralogists, and artists—thelist goes on.

A massive undertaking to beginwith, the book was translated fromJapanese to English. But it did con-tain some minor errors. In the listingfor the Searcy diamond, for example,there appears a photo of the Sancy. Inthe entry for “abraded culet,” theauthor likened it to an open culet,which I do not agree with. And see-ing entries on Gübelin, Kunz, andShipley made me wonder why Dana,Liddicoat, and Sinkankas were notincluded.

But as a general reference, thebook serves its purpose well. Theappendices alone are useful, coveringa wide range of subjects and provid-

ing charts on birthstones, ring sizes,hallmarks, and more. Overall, thisvolume would make a nice additionto any gemological library if cost isnot an issue.

JANA MIYAHIRA-SMITHGemological Institute of America

Carlsbad, California

Splendour and Science ofPearlsBy Dona Mary Dirlam and RobertWeldon, Eds., 139 pp., publ. by theGemological Institute of America,Carlsbad, California, 2013, US$89.00

The book delivers a broad overviewof the world of natural and culturedpearls. The well-researched and lav-ishly illustrated presentation coversthe history of pearls, world localities,classification, treatments, identifica-tion, fashion, and the future of theindustry. One chapter focuses on thestory of pearls in India, while anoth-er includes results from a GIAresearch study on natural pearls fromthe Arabian Gulf.

GIA LIBRARY STAFFGemological Institute of America

Carlsbad, California

Jewels from Imperial St.PetersburgBy Ulla Tillander-Godenhielm, 295pp., illus. publ. by Unicorn Press,London, 2012. US$80.00

Geared toward the jewelry historian,this thoroughly researched work is awindow into the world of theRussian imperial Romanovs, startingwith the reign of Empress Elizabeth(1741–1762), and ending with

Nicholas II in 1917. The authordetails in chronological order thejewelry and objects d’art manufac-tured in St. Petersburg during thisperiod. The book contains numerousphotos of the jewels and family por-traits from that era

GIA LIBRARY STAFF

Diamond Street: The HiddenWorld of Hatton GardenBy Rachel Lichtenstein, 364 pp., publ.by Hamish Hamilton, London, 2012.£20.00

Hatton Garden is a famous area inLondon where jewelry has beenmanufactured since medieval times,and it continues to be known as afine jewelry and diamond center.The author reveals the history of thejewelry trade there and offers storiesabout the people, culture, and lore ofthis fascinating district.

GIA LIBRARY STAFF

GEMOLOGICAL ABSTRACTS GEMS & GEMOLOGY SUMMER 2013S3

DIAMONDSAbenteuer Jakutien: Auf den Spuren der Diamanten

[Adventures in Yakutia: On the track of the diamonds].K. Erler and H. Vollstädt, Lapis, Vol. 38, No. 4, 2013, pp.18–25, 54 [in German].

This article starts with a brief history of Yakutian diamondproduction, from Mikhail V. Lomonosov’s theory of diamonddeposits in 1761 to the discovery of the first kimberlites in1954 to present-day operations. The bulk of the article thenpresents information the authors gathered during two visitsto Yakutia, focusing on Mirny.

The report contains a map and a list of data on the mostimportant mines. It is lavishly illustrated with images ofMirny—the mine, the town, the museum—and impressivediamond specimens.

RT

China market: The new frontier.Diamond World, Vol. 40, No. 2,Jan-Feb. 2013, p. 126-132

China, the world’s second-largest jewelry consumer after theUnited States, is also the second-largest jewelry manufactur-ing center after India. There is enormous potential for dia-mond jewelry in China, where the government has supportedthe industry through major policy decisions: reducing theVAT (value-added tax) on diamonds, abolishing importduties, and setting up the Shanghai Diamonds Exchange fortrading in rough and polished diamonds. The government hassigned multibillion dollar resources-for-infrastructure dealswith various African governments, securing its supply ofrough diamonds. These efforts have drawn a huge flow of cap-ital investment from diamond companies in Tel Aviv andAntwerp. Skilled diamond craftspeople have been brought infrom Surat, India, to train Chinese workers.

This section is designed to provide as complete a record aspractical of the recent literature on gems and gemology. Articlesare selected for abstracting solely at the discretion of the sectioneditors and their abstractors, and space limitations may requirethat we include only those articles that we feel will be of greatestinterest to our readership.Requests for reprints of articles abstracted must be addressed tothe author or publisher of the original material.The abstractor of each article is identified by his or her initials atthe end of each abstract. Guest abstractors are identified by theirfull names. Opinions expressed in an abstract belong to the abstrac-tor and in no way reflect the position of Gems & Gemology or GIA.© 2013 Gemological Institute of America

REVIEW BOARDEdward R. Blomgren

Asheville, North Carolina

Jo Ellen ColeVista, California

Edward JohnsonGIA, London

Michele KelleyMonmouth Beach, New Jersey

Guy LalousAcademy for Mineralogy, Antwerp, Belgium

Kyaw Soe MoeGIA, New York

Keith A. MychalukCalgary, Alberta, Canada

James E. ShigleyGIA, Carlsbad

Russell ShorGIA, Carlsbad

Jennifer Stone-SundbergPortland, Oregon

Rolf Tatje Duisburg, Germany

Dennis A. ZwigartState College, Pennsylvania

GEMOLOGICAL ABSTRACTS GEMS & GEMOLOGY SUMMER 2013 S4

Overall, China has cheaper labor costs than India, andits workforce provides better finishing of jewelry. Much ofthe work in Chinese jewelry factories is automated, andthe level of technology and infrastructure is higher thanin India. India produces every size and type of rough,while China mostly manufactures sawables. While Indiaholds the advantage in manufacturing, China is a majorconsumer of polished diamonds. China is also better atjewelry manufacturing. But there is no original Chinesebrand of international jewelry, and country needs bettercommunication with the outside world.

GL

The Ellendale diamond field: Exploration history, discovery,geology, and mining. A. L. Ahmat, The AustralianGemmologist, Vol. 24, No. 12, 2012, pp. 280–288

The Ellendale diamond field in West Kimberley is one ofonly three hard-rock diamond mine locations inAustralia. Though not the first Australian diamondmine, Ellendale was the country’s first hard-rockdeposit. It holds a special place in world diamond histo-ry as it led in November 1976 to the recognition of anew host-rock for diamond, olivine lamproite. Up untilthat time, commercial-sized diamonds were consideredto be sourced only from kimberlite. The Ellendale lam-proites are geologically very young, only 22 Ma (millionof years) old. Within several years of the initial discov-ery, some 46 lamproite pipes were found at Ellendale. By1980, 38 of these pipes had been assessed for their dia-mond content. More than two decades later, geologists from theKimberley Diamond Company (KDC) recognized eluvialdiamond enrichment over these pipes. After a lengthylegal battle, they wrested the Ellendale mining leasefrom the Ashton Joint Venture and commenced miningthere in May 2002. Ellendale is recognized as a source ofhigh-value fancy yellow diamonds. These high pricedstones have been marketed through a special deal withTiffany & Co since 2009. But the future of mining thereis tenuous. Ellendale 4 was closed in 2009, and the highAustralian dollar, combined with dwindling reserves,may jeopardize the survival of Ellendale 9.

GL

EOSFancy: Automatic bruting of fancy shapes. T. Geversand J. Vandeloo, De Belgische Diamantnijverheid,Jan/Feb/Mar 2013 Vol. 83, No. 1, pp. 14–16.

More than eight years ago, Belgium’s Scientific ResearchCentre for Diamonds (WTCOD) developed an automaticbruter for round diamonds. The bruting machine wasbased on a new principle: the application of a grindingwheel, rotating in a cooling liquid, to a rotating dia-mond. WTCOD has now expanded the scope of the EOSbruting machine to fancy shapes by linking the feedmovement of the disc to the rotating position of the dia-mond. With EOSFancy, one can brute any convex shape

with high accuracy and symmetry. The new softwarerequires a recent PC with a specific graphics card.EOSFancy can be used manually or via a transfer from arough scanner. The system can be used for both prebrut-ing and finishing, and it is the ideal complement to laserprebruting. With EOSFancy, a lasered girdle can be fin-ished perpendicular to the table with a result closer tothe end dimensions, with a shorter processing time. Thedevelopment is now in testing phase at a limited num-ber of Antwerp-based diamond companies. A commer-cial version is expected to be released by HRD during2013.

GL

Infrared microspectroscopy of natural Argyle pink dia-mond. K. S. Byrne, J. D. Anstie, J. Chapman, andA.N. Luiten, Diamond and Related Materials, Vol.23, 2012, pp. 125–129, http://dx.doi.org/10.1016/j.dia-mond.2012.01.032

One of the most distinctive characteristics of naturalpink diamond is the lamellae, or “graining,” in whichthe color resides. These features are believed to haveformed under plastic deformation. A great deal ofresearch has focused on color centers in diamond, partic-ularly the N-V center. This article investigates the crys-talline defect responsible for pink coloration in naturaldiamond. Infrared microspectroscopic images wereobtained to estimate the spatial distribution of B-centersin natural pink Argyle diamonds. The spatial distribu-tion of the nitrogen B-center (N–V–N3) was anti-correlat-ed with the intensity of pink coloration. The authorsbelieve this is the first such observation. IR spectral fea-tures were not influenced by exposure to UV illumina-tion, in contrast to the visible change in colorationunder the influence of UV radiation.

GL

Internal texture and syngenetic inclusions in carbonado.F. V. Kaminsky, R. Wirth, and L. Morales, TheCanadian Mineralogist, Vol. 51, No. 1, pp. 39–55,http://dx.doi.org/10.3749/canmin.51.1.39

Carbonado is a black or dark brown cryptocrystallineaggregate of diamond. Its age ranges from 2.6 to 3.8 Ga(billions of years), according to lead isotopic composi-tion. Carbonados have been found only in alluvial placerdeposits, such as those in Brazil and Central Africa, andnever in kimberlite. Many hypotheses, including non-kimberlitic, crustal origin of carbonado were proposedby previous researchers. Analysis of internal texture andsyngenetic inclusions is important to understanding thegenesis.

Carbonado samples were collected from alluvialplacer deposits of the Macaubas River basin in theBrazilian state of Minas Gerais and the Ubangi Riverbasin in the Central African Republic. They were darkor nearly black, with a smooth and shiny surface. The


samples contained pores ranging from a few hundrednanometers to a few micrometers. Secondary electronimages revealed a typical polycrystalline structure,which showed fine-grained texture with irregularlyshaped diamond grains averaging 5 to 15 µm. Grainboundaries were in irregular, zigzag patterns. Numerouspores, up to 20 µm, were found inside grain boundaries.They were usually filled with postgenetic minerals suchas kaolinite, flurencite, and quartz. Dislocation lineswere also observed within some diamond grains. Thepole figures suggested that crystallographic orientationsof these grains were quasi-random.

Syngenetic inclusions ranging from 10 to 50 nmwere identified using the combined FIB/TEM technique:garnet, apatite (including fluorapatite), phlogopite, silica,Ca-Mg-Sr- and Ca-Ba-carbonates, halides (sylvite, KCl,and bismocolite, BiOCl), native nickel and metal alloys(Fe-Ni, Cr-Fe-Mn, and Pb-As-Mo), oxides (FeO, Fe-Sn-O,TiO2, SnO2, and PbO2), Fe-sulfides, and fluid inclusions.An intergrowth of fluorapatite, phlogopite, and silicawas also observed. Almandine-pyrope garnet inclusionswith silica-enriched amorphous rims were confirmed.Fluid inclusions contained Si, Al, Fe, O, Ti, Ca, S, Cl, K,and carbonate. These fluid inclusions suggested the car-bonados were formed in a chloride-rich environment.Crystal inclusions were not pressure-indicator minerals.Instead, they were stable in a wide range, from crust tolower mantle, except bismocolite, which could only beformed in the crust. Although this whole inclusionassemblage was possibly of crustal origin, conclusiveresearch is still needed. The authors propose that thesesamples were crystallized and grown in one stage, whichwas followed by sintering. This hypothesis could be con-firmed by comparison with one-stage growth process ofa polycrystalline diamondite.

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GEM LOCALITIESAchate von der Teufelskanzel bei Oberthal im Saarland

[Agates of the Teufelskanzel near Oberthal,Saarland, Germany]. K Schäfer, Lapis, Vol. 38, No. 5,2013, pp. 14–21, 54 [in German].

The “Teufelskanzel” (Devil’s Pulpit), a rhyolitic promon-tory at Oberthal about 30 km (20 miles) southwest of Idar-Oberstein, is one of the many small agate deposits of theNahe-Saar Basin. A failed first attempt to mine the agatesin 1882 was followed by rather chaotic rockhound activi-ties and the equally unsuccessful decision by the commu-nity of Oberthal to take over all mining activities. Finally,digging for agates was generally prohibited, a ban that isstill in force.

The agates generally formed as thunder eggs. Theyshow a very beautiful coloration and often bizarre, pic-turesque forms that inspire the imagination of the behold-

er. Many also display a strong green long-wave UV fluores-cence, supposedly due to uranyl ions.

The beauty of the agates and their fluorescence areillustrated by a range of color photos.

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Montana moss agate: Collectible chalcedony from theYellowstone River. B. Britt, Rock & Gem, April,2013, Vol. 43, No. 4, pp. 34–37.

The expansion of various mining projects in Canada’sNorth (Northwest Territories, Yukon, and Nunavut) is setto lead the country in economic growth over the next twoyears. Spinoff activity that accompanies mine-relatedprosperity is also expected to increase based on pendingmines in the assessment phases or preproduction stages,thus further boosting employment and local economicdevelopment. Production in these areas is expected to lastwell into the coming decades. Environ mental groups andlocal residents are also interested in the impact on theCanadian North ecosystem as well as the long-termeffects on the towns and industry when the boom is over.

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Neufund: Blaue “Wolkenachate” von Weierbach bei Idar-Oberstein, Rheinland-Pfalz [New find: Blue “cloudagates” from Weierbach near Idar-Oberstein,Rhineland-Palatinate]. K. Schäfer, Lapis, Vol. 37,No. 6, 2012, pp. 25–29 [in German].

The agate deposits that formed the basis of the lapidaryand cutting industry at Idar-Oberstein until the 19th cen-tury are mostly depleted. What reaches the market todayis the result of rockhound activities. This article reportson a remarkable find from 2012 along a road constructionsite at Weierbach, near Idar-Oberstein. Found in a smalloutcrop of volcanic rocks, the nodules showed diametersof 2–12 cm (0.8–4.8 in.). While agates from Idar-Obersteingenerally have a fine banding and pastel tones, most ofthese agates were not banded but showed cloud-likestructures and striking sky blue and red colors. The arti-cle contains numerous images of the splendid agates andthe deposit.

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Wittichenite from the Cattle Grid Pit, Mount GunsonMine, South Australia. R. Noble[[email protected]], The MineralogicalRecord, March-April, 2013, Vol. 44, pp. 133–143.

In 1981, large, attractive wittichenite crystals found at theCattle Grid Pit in South Australia were mistaken for chal-cocite. Then in 2008, they were correctly identified by theSmithsonian Institution. Electron microprobe analysis ofthis species shows Cu, Bi, and S (weight percentages of38.67%, 41.70%, and 19.90%, respectively).

The Cattle Grid wittichenite is brittle, with stronglyconchoidal fractures and a relatively low hardness. Thecolors vary from highly lustrous silvery white to bronze to

GEMOLOGICAL ABSTRACTS GEMS & GEMOLOGY SUMMER 2013 S5GEMOLOGICAL ABSTRACTS GEMS & GEMOLOGY 2013 S5

a deep purple-black. The crystals are predominantly tabu-lar-prismatic in habit, but some show myriad crystal facesand deeply striated prisms. The Miller indices for thesecrystal forms, and their intricate and complicated crystalmorphology, are discussed in depth.

The article contains 16 large photos of wittichenite,some crystals weighing more than 75 grams, as well as themine site and the copper localization stratigraphy. Thenumber of wittichenite crystals larger than 2 cm in maxi-mum dimension is estimated to be about 30, and these areheld in only three collections (two institutional and oneprivate). Unfortunately, the entire production of coppersulfide concentrate from the Cattle Grid Pit is now ownedby a private smelter, where the bismuth-containing wit-tichenite is considered an undesirable impurity.

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INSTRUMENTS AND TECHNIQUESDetermining the geographical origins of natural emeralds

through nondestructive chemical fingerprinting. D.P. Cronin and A. M. Rendle. The Journal ofGemmology, Vol. 33, No. 1-4, 2012, pp. 1–13.

The technology to identify a gemstone’s geologic and geo-graphic origins has improved in the last decade to the pointwhere accurately pinpointing the locality has become areality. Using emeralds from different mines in theCordillera Oriental region of Colombia, some of them onlya few miles apart, scientists can now discern minute differ-ences in chemical composition and determine each sam-ple’s point of origin by studying the chemical “finger-prints” in their chromophores. The chromophores are traceelements of vanadium, nickel, or magnesium and vary geo-graphically as a result of interstitial fluid migration prior toprecipitation.

After recognizing that within-site chemical homo-geneity and cross-site chemical heterogeneity depended onthe amount of chromophores in the crystal structure, theauthors sought to find out if chemical heterogeneitybetween emerald mining localities was chemically uniqueand statistically provable based on chromophore compo-nents alone. Included in the study were emerald samplesfrom the Muzo, Cosquez, and Guali mines of Colombia,plus the Campo Verdes and Carnaíba mines in Brazil, andthe Chantete mine in Zambia. Consideration for sampleinclusion in this study involved the history of the host rockchemistry on the skeletal crystal structure, the occurrenceof trace elements that link emeralds to their point of origin,the subsurface geology, fluid-rock interactions and the geo-chemical processes leading to emerald formation.

The study concluded that element-based heterogeneityexists between the six emerald mining sites. Through theuse of an Amray scanning electron microscope (SEM) cou-pled to an EDAX energy-dispersive X-ray spectrometer(EDX), statistically significant chemical heterogeneity

between mine sites was revealed by a non-destructive testthat preserved the integrity of the sample.

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The yellow color center and trapped electrons in beryl. L.Andersson, [[email protected]], TheCanadian Mineralogist, 2013, Vol. 51, No. 1, pp.15–25, http://dx.doi.org/10.3749/canmin.51.1.15

Investigations continue into the cause of yellow color inberyl. The generally accepted explanation is that it is relat-ed to the charge-transfer between Fe3+ ions substituting foroctahedral Al3+ ions in the crystal and the surroundingoxygen ions.

Using electron paramagnetic resonance (EPR), anabsorption technique that uses magnetic fields to measuretransition energies in atomic defect centers, this studycontradicts the accepted interpretation, proposing an alter-nate model.

Although a strong EPR signal from octahedral Fe3+ ionscan be found in beryl of all colors, including colorless, thestudy determined that Fe3+ ions substituting for Al3+ at theoctahedral position cannot be the cause of the yellowcolor. There is, however, a signal unique to yellow berylthat comes from Fe3+ ions at a tetrahedral site.

The author proposes a simple model describing the oxi-dation and reduction processes involving iron electronstrapped in the crystal structure to explain the creation anddecay of the yellow color. This study discusses reinterpre-tations of other experimental findings that lead to differentexplanations for beryl’s colors

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SYNTHETICS AND SIMULANTSBlue spinel crystals in the MgAl2O4-CoAl2O4 series: Part I.

Flux growth and chemical characterization. V.d'Ippolito, G. B. Andreozzi ([email protected]), F. Bosi, and U. Hålenius, AmericanMineralogist, Vol. 97, No. 11-12, 2012, pp.1828–1833, http://dx.doi.org/10.2138/am.2012.4138

Synthetic CoAl2O4 spinel, a high-temperature oxide(melting point of 1955°C), is the most stable compound ofa family of spinel-structured oxides obtained from CO3O4at progressive increase of Al contents. High-quality spinelsingle crystals with compositions closely correspondingto the solid-solution series spinel sensu stricto (MgAl2O4)-cobalt spinel (CoAl2O4) were produced by flux growthmethod, with Na2B4O7 as the flux. Low cooling rates andlinear temperature profiles were applied in the thermalinterval 1200–800°C, followed by rapid cooling. Thermalruns were performed in a reducing atmosphere. Selectedcrystals were investigated by SEM/EDS X-ray mapping tocheck for compositional homogeneity and by electron-microprobe analysis to obtain the chemical formula.

Crystals were found to be chemically homogeneous


and entirely representing the MgAl2O4-CoAl2O4 solid-solution series, with the latter component ranging from7% to 100%. The saturation of the vivid blue colorincreased with total cobalt content, but no shift in colorhue was observed along the series. The unit-cell parame-ter a increased from 8.084 to 8.105 Å along the solid-solu-tion series. The observed linear increase of the a parame-ter was seemingly due to the higher CoAl2O4 component.This was a premature and misleading conclusion, howev-er, because structural changes in spinel may depend onboth chemical composition and inversion parameter,which in turn is a function of thermal history. The com-position of crystal products does not correspond to thecomposition of the starting oxide mixture: cobaltenriched in the crystals. A tentative explanation of thisbehavior is suggested by considering possible ionic poten-tial as well crystal field stabilization effects.

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Growth strategy for controlling dislocation densities andcrystal morphologies of single crystal diamond byusing pyramidal-shape substrates. A. Tallaire, J.Achard, O. Brinza, V Mille, M Naamoun, F Silva,and A. Gicquel, Diamond and Related Materials,Vol. 33, pp. 71–77, http://dx.doi.org/10.1016/j.dia-mond.2013.01.006

A single synthetic diamond crystal can be used as an elec-tronic device because of its properties, such as a highbreakdown field and thermal conductivity. However,defects, such as dislocation bundles, which were formedduring growth process, can cause current leakage, higherbandgap, and birefringence. Defect-free single diamondcrystal that is large enough to be used as an electronicdevice is difficult to grow using current methods. Forexample, the “threading dislocations” can be formed in aCVD diamond using (001)-oriented substrate. The authorsdemonstrated that these defects could be reduced by mod-ifying substrate’s shape and orientations.

Two type Ib HPHT-grown, pyramidal substrates, typeA and type B, were used to grow single CVD crystals inthis research. The {100} directions in type A substrate and{110} directions in type B were polished into inclined faceswith 20°, 30°, and 40° angles. Both possessed a square topmeasuring 200 x 200 µm2. Crystals were grown on thesesubstrates using plasma-assisted CVD technique withpower density of 100 W/cm3 and methane concentrationof 5% at 850°C, achieving a growth rate of 13 microns perhour.

After removal of the substrate, the fully grown CVDcrystals showed high transparency. Nitrogen-relateddefects were not detected. The inclined faces in type Asubstrate helped prevent twin sectors from reaching thetop face. The growth rates of the lateral and top faceswere 32.5 and 13.5 µm per hour, respectively. Whenthickness reached about 490 microns, the inclined facesstarted to disappear. The dislocations, originating from

the square top of a pyramidal substrate, were observed ina crystal grown on type A substrate with 20° dislocations.However, these dislocations were diverted toward theedges rather than the top. Photoluminescence imageshowed that the inclined faces effectively diverted thedirection of threading dislocations from {100} to {110}direction. Absence of sharp edges in these pyramidal sub-strates also helped in reducing dislocations. The lateralsurfaces had the highest growth rate and possessed “fishscale” morphology in type A grown crystals, a morpholo-gy not observed in type B crystals. A maximum thicknessof 2.2 mm could be achieved with a dislocation of 40° ontype B substrate. A crystal 1.70 mm thick containing verylow defects was achieved using type B substrate with 20°or 30° dislocations.

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Zircon et geikielite artificiellement étoilés du Sri Lanka[Zircon and geikielite from Sri Lanka with artificialstars]. J.-P. Gauthier, B. Rondeau, and T. Prada,Revue de l'Association Française de Gemmologie,No. 180, 2012, pp. 5–11 [in French].

Two asteriated cabochons acquired in Sri Lanka wereidentified as natural zircon and geikielite. But the six-rayed star had not been observed in natural star zircons,and the eleven-rayed star of the geikielite was crystallo-graphically “impossible.” Microscopic observation clearlyshowed both had been created by a fine scratching of thecabochon domes.

In both cases, the surfaces appeared to have been pro-duced by short parallel scratches. The center of each starwas a white spot, and their branches were short, some-times missing or undulating and hatched. The effect isformed mainly by diffraction at the scratches rather thanreflection from needles or hollow tubes, like in naturalstones. When the focus of the microscope is loweredsome millimeters from above the cabochon surfacethrough below the surface, the star gets finer and issharpest below the surface, in contrast to natural stars,where the sharpest star seems to hover above the surface.

The features described above, along with some othercharacteristics mentioned by Steinbach (2011), allow asafe distinction of scratched star stones from their naturalcounterparts mostly by simple observation with thenaked eye.

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