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Connoisseur's Choice: Diamond, Dutoitspan Mine,Kimberley, Northern Cape Province, South AfricaPaul W. Pohwat aa Department of Mineral Sciences , National Museum of Natural History, SmithsonianInstitution , Washington , DC , 20013 E-mail:Published online: 09 Dec 2013.

To cite this article: Paul W. Pohwat (2014) Connoisseur's Choice: Diamond, Dutoitspan Mine, Kimberley, Northern CapeProvince, South Africa, Rocks & Minerals, 89:1, 54-65, DOI: 10.1080/00357529.2014.842838

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54    ROCKS & MINERALS

The valley referred to by Williams in the quote above is the Valley of Diamonds, the inescapable valley in which the intrepid Sinbad was left to die and where

diamonds lay strewn on the ground. Animal carcasses were thrown into the valley by gem merchants; the diamonds stuck to carcasses that provided food for giant eagles. The eagles brought the carcasses out of the valley, and the gem merchants could then collect the diamonds that fell off of them. Sinbad escaped by hiding in a carcass that was carried away by one of the giant eagles. Of course, he also was carry-ing a bag of diamonds. As a child, this tale was a favorite of mine, especially as I imagined the birds to be pteranodons (it was my dinosaur phase). People have been taken in by scam-mers with stories just like the Valley of Diamonds. In fact, a group of well-heeled, influential Americans in the mid-nineteenth century fell for a scam concerning diamonds in a mysterious place such as the Valley of Diamonds.

The year was 1872, and a consortium of investors led by San Francisco banker William C. Ralston (of Comstock Lode fame) was excited by a new diamond find somewhere in “a remote section of the United States.” As reported by Ralston, two prospectors deposited diamonds and rubies worth $125,000 (in 1872 dollars) in the Bank of California for safekeeping. The prospectors, John Slack and Philip Arnold, were close-mouthed about the location of this diamond find but eventually agreed to conduct two people to the site for verification. However, these representatives would be taken blindfolded when the party reached a certain point in their journey. Once at the spot, more diamonds were found, and the party came back with glowing recommendations. The two prospectors then made a further offer to return to the field and bring back a few million dollars worth of diamonds. This was agreed upon, the diamonds were returned, and a small parcel was sent to Tiffany & Co. for examination. The parcel was valued at $150,000 by Tiffany’s, and a qualified mining engineer, in the person of Henry Janin, was dispatched with Slack and Arnold to check out the field. A mining engineer with a reputation for exposing mining fraud, Janin pro-nounced the diamond fields to be among the richest in the world. The two prospectors were bought out for $300,000,

D I A M O N D

Paul W. Pohwat, a consulting editor of Rocks & Minerals, is the collection manager (minerals) in the Department of Mineral Sciences at the National Museum of Natural History (Smith-sonian Institution).

Only in the . . . valley of Sinbad are diamonds strewn on the ground in such profusion that they are likely to stick in the toes of a barefooted traveler.

Gardner F. Williams in The Diamond Mines of South Africa(1904, p. 115)

CONNOISSEUR'SCHOICEPAUL W. POHWATDepartment of Mineral SciencesNational Museum of Natural HistorySmithsonian InstitutionWashington, DC 20013pohwatp@si.edu

Dutoitspan Mine, Kimberley Northern Cape Province, South Africa

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and investors were found who represented the cream of the financial world, including a representative of the Rothschild family. It all came to an end when Clarence King, who was the leader of the 40th Parallel Geological Survey and would later become the first director of the U.S. Geological Survey, found the property, located in northwestern Colorado, to be salted with diamonds as well as emeralds, rubies, and sap-phires. In fact, some of the diamonds were partially faceted, having come from faceting rejects. Thus ended the Great Diamond Hoax, and dreams of an American valley of Sin-

bad were dashed (Rickard 1932; Spence 1993). Ironically, diamonds were discovered in Colorado a century later.

Mysterious DiamondDiamonds have fascinated humans since the beginning of

history. The word diamond comes from the Greek adamas,meaning invincible. A rich, often contradictory mythol-ogy has been built around diamond, just a few examples of which will be mentioned here. Early Hindus believed that powder from a flawed diamond was poison whereas powder

Figure 1. The Oppenheimer Diamond from the Dutoitspan mine, Kimberley, Northern Cape Province, South Africa. At 253.7 carats the Oppenheimer is one of the largest and finest diamond octahedra on public display. The adamantine luster is very apparent in this image as are the rounded edges that indicate resorption. The specimen was donated to the Smithsonian Institution by Harry Winston, Inc. Smithsonian Institution specimen, Chip Clark photo.

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from flawless diamonds gave a person strength, beauty, hap-piness, and a long life. Powdered diamond has been said to be the main ingredient of the poison used by Catherine de Medici, although arsenic would be a better supposition, not to mention cheaper. The belief that diamonds are poison is thought to have originated in the diamond workings of In-dia to prevent laborers from absconding with them in their mouths or swallowing and recovering them at a later time (to put it politely). Another belief was that diamonds could be used to detect poisons. The diamond would attract par-ticles of poison that would coat the surface of the diamond and darken it because they could not penetrate the diamond. Then again, diamond is alleged to have supernatural heal-ing powers: wearing one in bed and heating it with body warmth would cure sickness, as would keeping one in the mouth (a contradiction of the diamond as poison myth), or just breathing on one, or wearing one next to the skin; dia-mond was also considered a cure for bladder problems. It has been said that diamond put into the mouth of a liar would cure this moral defect—something a majority of politicians are happy is untrue. Another belief, running somewhat con-trary to the healing story, is that if a diamond is held in your mouth, your teeth would fall out. Wearing a diamond was also believed to cure the insane and those possessed by evil spirits as well as guaranteeing a sleep free from nightmares. Having legal problems? Wearing a diamond was supposed to cause lawsuits to be settled in your favor. Touch a diamond to the corners of your house, barn, orchards, or land, and they would be protected from lightning, storms, and blight. Diamond was magical, as evidenced by its eerie glow at night after spending the day in strong sunlight, a property we now call phosphorescence (Bruton 1978). The most mystical of diamond’s properties is its hardness.

Diamond is the hardest naturally occurring substance known to man. It is interesting to note that Pliny the Elder, in the thirty-seventh book of his History of the World, noted, “The way to test the adamas is upon an anvil: since strike any point…with a hammer as hard as you can, it defies all blows” (Ball 1950, p. 138). Pliny also stated that the only thing that will affect diamonds is soaking them in the blood of a goat and then using a hammer to break them. He then goes on to say, “Personally, I would like to know who first soaked ad-amas in goat’s blood, whose mind thought of it?” a question I am sure we all ponder (Ball 1950, p. 139). Does this mean that you can beat a diamond with a hammer and nothing will happen? Absolutely not! Struck just right, diamond will cleave due to its perfect {111} cleavage, a property taken ad-vantage of by diamond cutters. Struck wrong and you have a smashed diamond. This story is also believed to go back to the early days of diamond mining, when unscrupulous gem merchants would convince the miners that what they had collected were not diamonds because they shattered with a hammer’s blow. When the miners left, the merchants would collect the fragments. To show how long old wives’ tales con-tinue to hold sway with the general public, Genth and Kerr (1885, p. 19) tell of three gold panners in North Carolina who came across a sizable black diamond and “In their ig-

norance, believing that it could not be broken, they smashed it to pieces.”

One final point concerning the hardness of diamond is the belief that only diamonds can scratch glass. This myth occurs not only in bad movies and books; it is repeated as gospel by people unfamiliar with basic mineralogy. It also has found a place in diamond mining lore. Discussing the discovery of diamonds in South Africa, Williams (1904, p. 120) wrote: “Perhaps O’Reily would have thrown the peb-ble away, if it had not come under the eye of . . . Mr. Lorenzo Boyes. Mr. Boyes found on trial that the stone would scratch glass.” We know that anything with a Mohs hardness of 5–5.5 and above will scratch glass, and yet this myth continues even with ready access to the Internet. This goes a long way to ex-plain why quartz (known as Herkimer Diamond and Pecos Diamond, for example) was mistaken for the real thing. As an aside, you have to be amazed by the Mohs hardness scale. How did Fredrick Mohs (1773–1839) get it so right in the early days of the science that became mineralogy? Develop-ing the scale in the eighteenth century, when so many of the mineral species we know today had not been discovered, Mohs was able to construct a scale of hardness that has quite literally stood the test of time. On this scale the top rank of 10 is diamond; given diamond’s extreme rarity during his lifetime, I am amazed Mohs had access to any at all.

Diamond, whose composition is carbon (C), is the only known native element that is a gemstone. This column will go light on the basic information for diamond because there are some great articles in this issue of Rocks & Minerals covering them in more detail than I can in this short col-umn. The basic information concerning diamond is given by Harlow (2014). Although the general public is enthralled by perfectly clear, colorless diamonds, it is the colored dia-monds that command the most interest of the connoisseur. The color of diamonds is caused by minor trace elements, which are covered in more detail in two articles in this is-sue: color by Gaillou and Rossman (2014), and inclusions by Koivula and Skalwold (2014).

Diamond CrystalsDiamond crystallizes as isometric crystals and occurs ei-

ther as single crystals, parallel growths, aggregates, or clus-ters of small crystallites. Collectors are fascinated by the many crystal habits of diamond. When I started doing re-search for this column, I had the simplistic view that there are two types of diamond—gem and industrial. It turns out that there are three principal types of diamond, based upon morphology and growth mechanisms, according to Tap-pert and Tappert (2011). These are (1) monocrystalline dia-monds, which occur as single crystals, aggregates, twins, and other intergrowths; (2) fibrous diamonds, which are made of numerous microscopic elongated fibers whose morpholo-gies are similar to monocrystalline diamonds; and (3) poly- crystalline diamonds, which consist of innumerable small crystallites usually occurring as indistinct masses. The in-formation that follows is from Tappert and Tappert (2011) unless otherwise indicated.

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The habits of most monocrystalline diamonds are the octahedron, the cube, and the rhombic dodecahedron, with the most common being the octahedron, ideally with eight equal-sized triangular faces. But, as with most natural min-erals, the octahedra are commonly distorted, with some so distorted that the crystals appear flat. The octahedral habit is indicative of the diamond growing slowly under somewhat stable conditions. Many octahedral diamonds are modified by resorption, a loss of volume of the crystal, which took place after formation. Kimberlite magma contains high concentrations of carbon dioxide and water, which under high temperature causes diamonds to be partially or totally resorbed. The features of resorption are seen as curved crys-tal edges and corners; as resorption progresses, the crystal faces are affected, gradually disappearing and becoming rounded dodecahedra. It is interesting to note that diamond crystals still embedded in xenoliths are relatively unaffected by resorption. There are cases where the part of the crys-tal still embedded in a xenolith retains the octahedral habit whereas the other portion of the crystal exhibits a dodeca-hedral habit. These crystals are called pseudohemimorphic (Stachel 2007).

Not as common as octahedra are cubic diamond crys-tals, which are more properly described as cuboid. The faces of cuboid monocrystalline diamond crystals have a rugged appearance with rounded edges and faces that look like some-one inexperienced in chain-saw artistry tried to carve them. The faces may curve inward (called reentrant) or outward (called salient). The outward curve of the faces may be so intense that the crystals appear to be a tetrakis hexahedron. Internally, monocrystalline cubes may show the cubic growth interrupted by octahedral growth. However, cuboctahedral crystals of monocrystalline diamond are very rare (see Rako-van et al. in an upcoming issue). Monocrystalline diamond cuboids are also subjected to resorption, which causes the corners and edges of the cube to be rounded. As resorption progresses, the cube faces and edges disappear and the crys-

tal develops a dodecahedral or tetrahexahedral habit. Only a small number of deposits have produced diamond cuboids in quantity.

As discussed, dodecahedra of monocrystalline diamond result from resorption of octahedral and cuboid diamonds. The size of dodecahedral diamonds is determined by two factors: the original crystal habit and the extent of resorp-tion. It is interesting to note that the faces of dodecahedral diamonds are always curved; there is no distinct, flat crystal face. To define a crystal crystallographically, you need planar faces to which a distinct pole is perpendicular to the face; curved faces have an infinite number of poles. This has led to the suggestion that these diamonds should be called do-decahedroids and tetrahexahedroids (Stachel 2007). Resorp-tion may also reveal original growth zones that may not be

Figure 2 (left). Highly resorbed cuboid diamond weighing 11.65 carats, from Botswana. North Star Minerals specimen, Jeff Scovil photo.

Figure 3 (center). A resorbed diamond cuboid weighing 11.65 carats, from Botswana. The knobs mark the position of former octahedral faces. North Star Minerals specimen, Jeff Scovil photo.

Figure 4 (right). A resorbed diamond cuboid weighing 11.65 carats, from Botswana. North Star Minerals specimen, Jeff Scovil photo.

Figure 5. Fibrous diamond cuboid 1.5 cm on edge, from South Africa. Note how the surface and edges look like they were made by a chain-saw artist. Smithsonian Institution specimen, Ken Larson photo.

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noticed in normal light but may be observed by using ultra-violet light.

Diamonds that do not show a definite crystal habit or an incomplete habit are termed irregular diamonds. Irregular diamonds possess a smooth undulating surface. It is interest-ing to note that most of the world’s largest diamonds, such as the Cullinan, are irregular diamonds. Recently, a large irreg-ular diamond, weighing 1,138 carats, from the Democratic Republic of the Congo was examined by GIA labs (King and Wang 2013).

The biggest surprise to me were fibrous diamonds, which consist of microscopic parallel fibers that normally cannot be seen without magnification. They have a distinct dull ap-pearance and are nontransparent or opaque, properties that are useful in identifying them. Frequently, the fibers form a coat on the outer layer of monocrystalline diamonds. The coated diamonds are quite often sharp octahedral crystals. Fibrous diamonds may grow in concentric layers; diamonds displaying obvious concentric layering are referred to as hail-stones or hailstone boart. Fibrous diamonds with a spherical habit are called ballas, with the fibers usually radially ori-ented around the center. The habits of fibrous diamonds are similar to monocrystalline diamond cuboids, with rough surface features and rounded edges. This makes visually dis-tinguishing between the two extremely difficult. The habit of coated diamonds is influenced by the thickness of the coat and the habit of the enclosed diamond. Thin fibrous coats on octahedral diamonds will not change the octahedral habit; thicker coats will produce cuboctahedral or cuboid habits. Fibrous diamonds and diamonds coated by fibrous diamond are minor components of many deposits; some deposits lack them entirely.

Polycrystalline diamonds are made up of microcrystal-line to cryptocrystalline diamonds, usually in nondescript masses. Polycrystalline diamonds include framesites, which consist of diamond grains that are greater than 100 mi-crometers in size (some of which may be euhedral) that are surrounded by a matrix of small grains less than 20 microm-eters. Some framesite is porous, and the voids are some-times lined with euhedral diamond crystals. A subvariety of framesite with finely dispersed inclusions of magnetite is called stewardite. Another type of polycrystalline diamond is carbonado, which is more porous and has a smaller grain

size than framesite. Because of the numerous minerals lin-ing the pore spaces of carbonado, it is typically black, dark gray, or brown in color. Yakutite is a polycrystalline diamond that has an abundant amount of lonsdaleite, the hexagonal polymorph of diamond that is a component of meteorites and shock metamorphosed rocks, thus lending strong sup-port to the theory that yakutites are formed by meteoritic impact. Note that framesite, stewardite, and yakutite are va-rietal names not species names.

Any conversation about diamond crystals is incomplete without a discussion of twins and the unusual surface fea-tures of diamond. Twinning can be either contact or pen-etration. Collectors are familiar with the flattened contact twins called macles. These are flattened spinel-law twins that are distinguished from simple flattened octahedra by the presence of a twin plane. The orientation of two macles in opposite directions produces a Star of David shape. Pen-etration twins are common in diamonds with a cubic habit and may occasionally be found in diamonds with an octa-hedral habit. Twins are also affected by resorption and will

Figure 6 (far left). Fibrous diamond cuboid 1.3 cm on edge, from South Africa. Martin Zinn specimen, Jeff Scovil photo.

Figure 7 (left). A spherical 1.1-cm-high coated dia-mond, called ballas, from Brazil. Martin Zinn speci-men, Jeff Scovil photo.

Figure 8. Diamond spinel-law twin called a macle, 1.4 cm high, locality unknown. The triangular shape is characteristic of macles. Note the triangular markings on the surface called trigons. Green Mountain Minerals specimen, Jeff Scovil photo.

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develop a dodecahedroid habit just as single crystals do. The distinguishing characteristic of dodecahedroid twins is the presence of the twin plane. Often confused as twinning are diamond crystals in parallel growth, where the crystals are oriented in the same direction but not in controlled crystal-lographic directions.

Diamonds have distinctive surface features. Those most commonly observed on octahedral diamonds are called trigons. These triangular features range in size from micro-scopic to macroscopic. Some faces that appear to be pristine will be seen to have trigons upon microscopic examination. As you observe trigons on an octahedral face you’ll note that they are oriented opposite to the face they occur on and are referred to as negative trigons (positive trigons are extremely rare). Negative trigons are believed to be formed by etch-ing from fluids over 1,000°C. Trigons are not to be confused with triangular plates, which are growth features of variable thickness that can occur as single or multiple layers. When occurring as multiple layers, they give the diamond crystals a stepped appearance. Shield-shaped laminae also can be found on some octahedral crystal faces; they are smaller than the crystal face they occur on and have curved edges, which give them their appearance. Multiple layers of shield laminae will also give a stepped appearance to the diamond crystal. Cuboid diamond crystals have tetragonal pits referred to as tetragons. On dodecahedroid crystals, hillocks are a com-mon surface feature. They may range from pyramidal to tear-drop shaped.

Before moving on to the locality listing, let me say that I cannot recommend highly enough Tappert and Tappert’s 2011 book Diamonds in Nature: A Guide to Rough Diamond. It has been of inestimable value to me while researching this section of the column, and it is definitely the finest available reference I have read dealing strictly with rough diamonds.

Where Diamonds Are FoundThe first diamonds were found in and mined from alluvial

deposits—river gravels and sand, sandstone, and conglom-erate from which the diamonds of India were mined. The Indian deposits are mainly on the eastern side of the Deccan Plateau (Bauer 1970). It is not known when diamonds were initially found in India. The first mention of them was made by Jean-Baptiste Tavernier who visited the diamond mines sometime between 1630 and 1668. The area referred to as Golconda, from the Godivari River in Hyderabad (present-day Andhra Pradesh) to the Pennar River, is where the most famous Indian diamonds have been recovered (Webster and Anderson 1983). There is only one diamond specimen from India in the Smithsonian collection (besides the Hope Dia-mond, which is the subject of an article in this issue by Post and Farges), and that is a conglomerate from the district of Karnul, in Madras (now known as Chennai), Tamilnadu. The specimen, at one time in the Carl Bosch collection, is a conglomerate that contains a fractured diamond. The mines of the Karnul district were some of the most important, as noted by Bauer (1970). Another Asian locality that has pro-duced alluvial diamonds is Indonesia, which is known to have produced diamonds since 600 (Webster and Anderson 1983). In the collection is a “specimen” with no specific lo-cality given; it is a vial with numerous dodecahedroids.

The deposits of Brazil were discovered in 1725 at Tejuco (now Diamantina) and became the second major source of diamonds. Brazilian diamonds occur in alluvial deposits along river banks and in conglomerates and sandstones. Be-sides the diamond deposits in Minas Gerais, diamonds have also come from the states of Bahia, Mato Grosso, Goyaz, Ma-ranha–no, and Paraná. There are some diamonds from Brazil in the collection, in particular a suite originally in the Carl Bosch collection. These specimens are not of great size, run-

Figure 9 (left). An 8.23-carat diamond octahedron showing triangular growth on the faces, from South Africa. Jerry Rosenthal speci-men, Jeff Scovil photo.

Figure 10 (right). A fine gem-quality diamond octahedron 1.4 cm high displaying trigons and resorption along the edges of the crystal, from South Africa. Martin Zinn specimen, Jeff Scovil photo.

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ning in the 3-mm range, but they are nice crystals, mainly octahedra. Also in the Smithsonian collection are two Bra-zilian specimens of conglomerate that contain diamonds. One is a recent acquisition with a diamond approximately 1 cm in size. When deciding whether to acquire a matrix specimen, always check to be certain the diamond belongs in this matrix. Besides the telltale glue-sand mixture, check the diamond itself for surface features that are typical of alluvial diamonds such as edge and surface abrasion, scratches, per-cussion marks, and cleavage surfaces. As noted by Sinkankas (1972), regard all matrix diamond specimens with suspicion and examine a specimen closely before acquiring it. One specimen in particular made me appreciate the skill of the miners back in the day, as the younger crowd is wont to say. In the collection is a rather large corked bottle of “diamond gravel.” Listed only as Brazil in the catalogue, the bottle con-tains mineral fragments to 2 mm within which are diamond fragments and crystals. I examined some portions of the contents of this gravel and found one diamond crystal in the material I sampled. (Because I was doing this exercise with modern microscopes, I gained a greater appreciation for the skill possessed by the miners of yore.) In the 1960s more than fifty kimberlite pipes were discovered in the Dia-mantino, Mato Grosso, area (Moore 2004). Another alluvial diamond locality in South America is Venezuela, which pro-duced five specimens now in the collection. Two are recent acquisitions from Santa Elena, Bolivar State; both display incredible clarity. Both also show marks typical of alluvial diamonds (e.g., pitting, scratches, abraded edges). Another specimen from Santa Elena is a dark gray, waterworn cube approximately 2 cm on edge.

It was not until 1871 that diamonds were discovered in South Africa in situ in a rock called kimberlite. Kimberlite was first described by Carvill Lewis from samples of dia-mond-bearing rock found at Kimberley, South Africa. He described the rock as brecciated with an abundance of shale inclusions; his conclusion was that the diamonds formed as secondary minerals through the reaction of the heat and pressure from the kimberlite on the carbonaceous shale (Jo-hannsen 1938). Now we know that diamonds found in kim-berlites are not formed in the kimberlite but rather in the Earth’s mantle, approximately 150–200 kilometers below the Earth’s surface. A quandary for petrologists was to determine which minerals belong exclusively to the kimberlite magma and which do not (Blatt and Tracey 1997). It has been noted that kimberlites are not a magma at all but a complex mix of megacrystals, a fine-grained matrix that has been altered by hot CO

2 and H

2O-rich fluids and polycrystalline fragments

derived from an assemblage of entrained xenoliths (Hess 1989). The mantle rocks are found as xenoliths in the kim-berlite and can be separated into two different rock types: eclogite (composed mainly of garnet and clinopyroxene) and peridotite (composed mainly of olivine and orthopyrox-enes) (Kirkley 1998; Moore 2004). It was through studying these xenoliths and also by close study of inclusions within the diamonds themselves that petrologists were able to de-termine that diamonds are formed in these rock types that make up the xenoliths, and they are essentially passengers on the long ride to the surface.

The diamonds of South Africa are described in detail by Bruce Cairncross (2014) in this issue, but there is one South African diamond that deserves special treatment. The featured specimen for this column is the 253.7-carat Oppenheimer Diamond, found in the Dutoitspan mine, Kimberley, South Africa. It was one of the specimens selected for Peter Ban-croft’s The World’s Finest Minerals and Crystals (1973), and while many of the specimens depicted in this book have long since been eclipsed by better examples, the Oppenheimer is still one of the finest mineral specimens in the world. The dia-mond was a gift to the museum from Harry Winston and named for Sir Ernest Oppenheimer (1880–1957), former chairman of the board for De Beers Consolidated Mines and the person credited with bringing De Beers into the twenti-eth century (Kanfer 1993). The specimen has a yellow color and shows some signs of resorption. It is presently on display in the National Gem Collection Gallery.

The Democratic Republic of the Congo (formerly Zaire, formerly Belgian Congo) accounts for a large percentage of the world’s diamond production. Much of this is from the alluvial deposits from the Tshikapa (or Kasai) area, along the Kasai River, discovered in 1907. This area has been a steady producer of diamonds up to the present time. In 1946, kim-berlites were discovered 300 kilometers east of Tshikapa at the Mbuji-Mayi (or Miba) deposit in Kasaï-Oriental Prov-ince (Levinson 1998). Diamond crystals from here present an incredible array of habits—cuboids, octahedra, dodeca-hedroids, and penetration twins. Many of the crystals ap-pear to have a coat of fibrous diamond. The Smithsonian

COLOR SPONSORS for the Connoisseur’s Choice column during 2014 are the Houston Gem and Min-eral Society, in memory of Arthur E. Smith, and the Cincinnati Mineral Society.

Other localities for alluvial diamonds include Sierra Le-one, where all the diamonds are alluvial (Moore 2004). In the Smithsonian collection is a specimen of parallel growth crystals approximately 1.5 cm across with triangular growth on some of the octahedral faces; no specific locality is noted for the piece. Also with no specific locality designation is a coated 82.3-carat cube that is on display.

Most of the diamond finds within the United States are confined mainly to diamonds found within alluvial depos-its, some of glacial origin. The Smithsonian collection con-tains diamonds from Cabin Fork Creek, Montpelier, Adair County, Kentucky, represented by a rounded octahedron, and from Rutherford County, North Carolina, represented by a dodecahedroid. Also represented by a dodecahedroid is Huntsville, Walker County, Texas, as are Brown County, Illinois; Diamond Basin, Owyhee County, Idaho; and Wed-derburn, Curry County, Oregon. Besides the Rutherford County find, Genth and Kerr (1885, pp. 18–19) have listed two octahedral crystals found at Brindletown Creek, Burke County, and a near-perfect crystal “of the first water.”

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collection contains a number of diamond crystals from the Kinshasa mine, Kinshasa Province. Besides being examples of coated crystals, they present a variety of colors and habits.

Russia has produced a prodigious quantity of diamonds as well. Diamonds were found in the Ural Mountains in Perm Kray in 1829, as well as in other places after that (Hin-tze 1904). It was not until 1947 that major exploration for diamond began. The payoff came in 1954 when the first kim-berlite was found in the Daldyn area, Yakutia (now Sakha) Republic. This first pipe was named Zarnista (dawn), and its discovery was followed in 1955 by the discovery of the Mir (peace) and Udachnaya (success) kimberlites. There are now approximately one thousand kimberlite bodies known in Si-beria; of these the most famous pipes are Mir, Internation-alnaya, and Udachnaya. Mir (also found spelled on labels as Myr or Mirny) is probably the most familiar to collectors, as it was a major diamond mine starting in 1957. Operations at the site have ceased, and specimens are now harder to find (Levinson 1998). If you find a good one, do not delay too long in acquiring it. Diamonds from the Mir pipe were avail-able as octahedra, macles, and parallel growths. In the col-lection there is one super Mir specimen that is a textbook example of a spinel twin; it is 9 mm on edge. It was acquired in 1980 and is of interest to me because I had to repair it in 1985 after the twin popped out of the matrix. I glued it back into its pyrite-lined cavity with a thinned epoxy, placed a repaired note in the tray with it, and never thought of it again until we started specimen selection for the new exhibit in 1994, by which time the pyrite lining the cavity as well as numerous pyrite blebs (for lack of a better word) had de-teriorated badly, leaving the once-proud xenolith destroyed. Other examples of Mir diamonds in the collection include a 5-mm colorless octahedron with a triangular growth layer on each of the exposed crystal faces, and another octahedron

approximately 1 cm on edge of a grayish color. There are two octahedral diamond crystals from the Aikhal pipe, also in the Sakha Republic, on display. One is a very fine dark gray octa-hedral crystal approximately 1 cm on edge.

Fine, though small, diamond octahedra have been found in the kimberlite of the Chagma mine, Mengyin, Shangdong, China. These specimens were plentiful back in the mid-1990s but are extremely hard to find now. The specimens in the collection contain octahedra to 3 mm in the rock, al-though specimens weighing 33 carats have been found (Ot-tens 2008). Dips in acetone have not loosened the crystals from the matrix.

If I were writing this column thirty years ago, the only site in the United States to find diamonds in situ would have been Murfreesboro, Arkansas. In May 1996, production be-gan at Kelsey Lake, State Line kimberlite district, Larimer County, Colorado. Approximately thirty diatremes have been identified straddling the Colorado-Wyoming border, with most of them in Colorado. The diamond crystals from Kelsey Lake are commonly octahedra, many with triangu-lar growth plates on the faces, and dodecahedroids. Macles and penetration twins are common as well. Colors range from colorless to white, green, yellow, and pale orange. Many of the crystals fluoresce (Eckel 1997). The example in the Smithsonian collection is a slightly distorted octahedron with distinct trigons on some of the faces. It is approximately 1 cm on edge and was pictured (in the center) on the 2002 Denver Mineral Show poster.

Who would also have guessed thirty years ago that diamonds would be discovered in minable quantities in Canada? Canadian diamonds from the Ekati mine, Lac de Gras, Northwest Territories, are available from some deal-ers—I recommend that you get one now while dealers have them because, like the Kelsey Lake diamonds, they are

Figure 11 (left). An octahedral diamond 1 cm on edge in xenolith, from the Mir pipe, Sakha Republic, Russia. Jim and Gail Spann speci-men, Jeff Scovil photo.

Figure 12 (right). Close-up of the diamond in figure 11 showing minor resorption along the exposed crystal edges and faces. Jim and Gail Spann specimen, Jeff Scovil photo.

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62    ROCKS & MINERALS

going to be few and far between. The pipe was discovered in the 1990s and has produced a wealth of diamonds not only for the diamond industry but for collectors as well. My personal favorites in the collection, after the Oppenheimer, are two incredibly clear macles, one of which shows signs of resorption. Also in the collection is an octahedron 5 mm on edge.

Although kimberlites are the main rock in which dia-monds are found in economic quantities, there is one other rock from which diamonds have been mined profit-ably: lamproite. In the past, lamproites were not considered sources for diamonds. Lamproites are ultrapotassic rocks

that typically contain one or more of the following minerals: olivine, diopside, phlogopite, leucite, sanidine, and richterite (Hess 1989). While kimberlites are usually found as cone- or carrot-shaped bodies, lamproites have champagne or mar-tini glass–shaped bodies. Two major diamond deposits are located in lamproite—Argyle and Murfreesboro.

The Argyle diamond mine (also labeled as the AK-1 pipe), East Kimberley Province, Western Australia, Australia, is one of the largest diamond producers in the world. Full-scale mining began in 1986, with 5 percent of the production con-sidered gem-quality, around 40 percent cheap gem-quality, and 55 percent industrial-grade (Keller 1990). The majority of the diamonds from Argyle are brown (if the brown dia-mond is of gem-quality, the color is now referred to as cham-pagne or cognac); yellow accounts for most of the rest of the production. However, Argyle is noted worldwide for its rare pink diamonds and the occasional green or red diamond. The common habit of the diamond crystals from Argyle is a strongly resorbed and fractured dodecahedroid with deeply etched channels. Macles are decidedly rare at the Argyle mine, and cuboids have not been found. Argyle diamonds fluoresce blue or dull-gray under ultraviolet light, with those fluorescing strongly blue also phosphorescing yellow. Pink Argyle diamonds are characterized by irregular frosted cleav-age cracks, pitted surfaces on narrow voids, and channels on the crystal surfaces (Keller 1990). The Smithsonian recently received a gift of a small parcel of Argyle diamonds for use in the research collection. Among the dodecahedroids was a small pink diamond that exhibited the characteristics men-tioned above. On display is a resorbed light brown octahe-dron 1.5 cm on edge.

The Murfreesboro, Pike County, Arkansas, locality is more properly named Crater of Diamonds State Park. The discovery of the Argyle deposit caused petrologists to reex-amine the Crater of Diamonds, once considered a kimberlite

Figure 14 (left). A 1.83-carat diamond octahedron from Kelsey Lake, Larimer County, Colorado. Dave Bunk Minerals specimen, Jeff Scovil photo.

Figure 15 (center). A 2.22-carat resorbed octahedron from Kelsey Lake, Larimer County, Colorado. Dave Bunk Minerals specimen, Jeff Scovil photo.

Figure 16 (right). A 7.18-carat octahedron from Kelsey Lake, Larimer County, Colorado. Note the uneven octahedral faces. Dave Bunk Minerals specimen, Jeff Scovil photo.

Figure 13. A 6.45-carat diamond from Kelsey Lake, Larimer County, Colorado, showing trigons and slightly resorbed edges. Smithsonian Institution specimen, Ken Larson photo.

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Volume 89, January/February 2014    63

pipe, and pronounce the diamond-bearing rock a lamproite. Diamonds were first found in Crater of Diamonds in 1906, and although there have been attempts to mine the lamproite, none have proved economically viable (Howard and Houran 2008). The Smithsonian’s diamonds from Crater of Diamonds all appear to be strongly resorbed dodecahedroids. The best is a 1.5-cm, 17.85-carat yellow crystal that originally was in the Washington A. Roebling collection. There is a small macle on display along with a suite of other dodecahedroids. The color of the Smithsonian’s Arkansas diamonds runs from colorless to yellow, brown, and dark brown. A final note about Crater of Diamonds is that you can still collect there, for a fee. In fact, on 13 July 2013, a twelve-year-old found a 5.16-carat brown diamond, the largest recovered in the past two years (Glen Worthington, pers. comm., 2013) (see photos p. 5, this issue).

Devotees of Connoisseur’s Choice may remember that diamond was the topic of an earlier column by Dr. Robert Cook (2000). Because this year’s Tucson Gem and Mineral Show is celebrating its sixtieth (diamond) anniversary, we thought a revisit to that species was in order. If you have access to the previous column, I recommend you go back

and reread it, as it complements this current column quite nicely.

ACKNOWLEDGMENTSAs already mentioned, my views concerning diamonds were

initially simplistic, but researching this column has been a true learning experience. I thank first the reviewers of the column, the steadfast troika of John S. White of Stewartstown, Pennsylvania, Dr. Robert Cook of Auburn, Alabama, and Dr. Carl Francis of Brain-tree, Massachusetts. Additionally, I thank Dr. Eloïse Gaillou, associ-ate curator at the Los Angeles County Museum of Natural History, for assistance in editing the column. For images I thank Jeff Scovil, Ken Larson, and the late Chip Clark. Conversations with Dr. Jeffrey Post, of the Smithsonian, were helpful in putting together the text. I am extremely thankful to Marie Huizing for her wealth of patience. And finally, to you, the readers of this column, I am grateful for your thoughtful and kind emails; it is good to know someone actu-ally reads what I write.

REFERENCESBall, S. 1950. Roman book on precious stones: Including an English mod-

ernization of the 37th booke of the historie of the world by G. Plinius Secundus. Los Angeles, CA: Gemological Institute of America.

Bancroft, P. 1973. The world’s finest minerals and crystals. New York, NY: Viking Press.

Figure 17 (right). The 17.85-carat, 1.5-cm-wide, yellow dodecahedral dia-mond from Crater of Diamonds State Park, Pike County, Arkansas, on dis-play in the Smith-sonian Institution. Smithsonian Insti-tution specimen, Chip Clark photo.

Figure 18 (far right). Resorbed yellow dodecahedral diamond approxi-mately 9 cm high, from the Crater of Diamonds State Park, Pike County, Arkansas. Max and Jon Sigerman specimen, Jeff Scovil photo.

Figure 19 (below right). A selection of diamonds from Crater of Diamonds State Park, Pike County, Arkansas, showing various stages of resorp-tion. The diamonds weigh a total of 4.95 carats. Matilda and Karl Pfeiffer Foun-dation Museum specimens, Jeff Scovil photo.

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Bauer, M. 1970. Precious stones, trans. L. J. Spencer. New York, NY: Charles E. Tuttle Company.

Blatt, H., and R. J. Tracey. 1997. Petrology: Igneous, sedimentary, and metamorphic. 2nd ed. New York, NY: W. H. Freeman and Company.

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Cook, R. B. 2000. Connoisseur’s choice: Diamond, Jagersfontein mine, Free State Province, South Africa. Rocks & Minerals 75 (2): 344–49.

Eckel, E. B. 1997. Minerals of Colorado. Updated and revised by R. R. Cobban et al. Golden, CO: Fulcrum Publishing.

Gaillou, E., and G. Rossman. 2014. Color in natural diamonds: The beauty of defects. Rocks & Minerals 89:66–74.

Genth, F. A., and W. C. Kerr. 1885. Minerals and mineral localities of North Carolina. Raleigh, NC: Board of Agriculture.

Harlow, G. E. 2014. Diamond: The super mineral. Rocks & Minerals 89:35–39.

Hess, P. C. 1989. Origins of igneous rocks. Cambridge, MA: Harvard University Press.

Hintze, C. 1904. Handbuch der mineralogy. Erster band. Erste abthei-lung. Elemente und sulfide. Leipzig, Germany: Verlag Von Veit & Co.

Howard, J. M., and J. Houran. 2008. Crater of Diamonds, Pike County, Arkansas. In American mineral treasures, ed. G. A. Stae-bler and W. E. Wilson, 74–79. East Hampton, CT: Lithographie.

Johannsen, A. 1938. A descriptive petrography of the igneous rocks. Vol. 4. Chicago: University of Chicago Press.

Kanfer, S. 1993. The last empire. New York: Farrar, Straus, and Giroux.Keller, P. C. 1990. Gemstones and their origins. New York, NY: Van

Nostrand Reinhold.King, J. M., and W. Wang. 2013. Lab notes: A very large rough dia-

mond. Gems & Gemology 49 (2): 116–17.

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Post, J. E., and F. Farges. 2014. The Hope Diamond: Rare gem, his-toric jewel. Rocks & Minerals 89:16–25.

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Rickard, T. A. 1932. A history of American mining. New York, NY: McGraw-Hill Book Co.

Sinkankas, J. 1972. Gemstone and mineral data book. New York, NY: Winchester Press.

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Tappert, R., and M. C. Tappert. 2011. Diamonds in nature: A guide to rough diamonds. Berlin, Germany: Springer-Verlag.

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Williams, G. F. 1904. The diamond mines of South Africa. New York, NY: Macmillan. ❑

51st Annual

Delaware Mineralogical Society

Gem, Mineral &

Fossil Show

March 1 & 2, 2014

Saturday 10:00 am - 6:00 pm

Sunday 11:00 am - 5:00 pm

Delaware Technical and Community College

400 Churchmans Rd.; Stanton, DE 19713

(Exit 4B, I-95)

Adults $6.00, Seniors $5.00, Juniors (12-16 yrs) $4. Children under 12 accompanied by adult– Free.

Dealers, Demonstrations, Exhibits

Info & Coupons at: www.delminsociety.net

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