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Gemstone

http://en.wikipedia.org/wiki/GemstoneJump to: navigation, searchFor other uses, see Gemstone (disambiguation).

"Jewels" redirects here. For the lice !ine song, see Jewels (song).For the ballet Jewels, see Jewels (ballet).

Gemology and Jewelry Portal 

gemstone or gem, also called a precious or semi-precious stone, is a piece o

attractive mineral, which # when cut and polished # is used to make  $ewelr% or other

adornments.&' owever certain rocks, (such as lapis*la+uli) and organic materials (suchas amber  or $et) are not minerals, but are still used or $ewelr%, and are thereore oten

considered to be gemstones as well. ost gemstones are hard, but some sot minerals are

used in $ewelr% because o their lustre or other ph%sical properties that have aestheticvalue. -arit% is another characteristic that lends value to a gemstone.

selection o gemstone pebbles made b% tumbling rough rock with abrasive grit, in arotating drum. he biggest pebble here is 0 mm long ('.1 inches).

Contents&hide

• ' 2haracteristics and classiication

• 3 4alue o gemstones

• 5 Grading

• 2utting and polishing

• 6 Gemstone color 

• 1 reatments applied to gemstones 

o 1.' eat

o 1.3 -adiation

o 1.5 7a8ing/oiling

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o 1. Fracture Filling

• 9 %nthetic and artiicial gemstones

• ; ee also

•

< !otes• '0 =8ternal links

[edit] Characteristics and classification

Gemstones are described b% gemologists using technical speciications. First, what is its

chemical composition. >iamonds or e8ample are made o carbon (2) and rubies oaluminium o8ide (l3?5). !e8t, man% gems are cr%stals which are classiied b% their

cr%stal s%stem such as cubic or trigonal or monoclinic. nother term used is habit, the

orm the gem is usuall% ound in. For e8ample diamonds, which have a cubic cr%stals%stem, are oten ound as octahedrons.

Gems are classiied into dierent groups, species, and varieties. For e8ample, rub% is thered variet% o the species corundum, while an% other color o corundum is consideredsapphire. =merald (green), a@uamarine (blue),  bi8bite (red), goshenite (colorless),

heliodor  (%ellow), and morganite (pink) are all varieties o the mineral species ber%l.

Gems have reractive inde8, dispersion, speciic gravit%, hardness, cleavage, racture, andlustre. he% ma% e8hibit pleochroism or double reraction. he% ma% have luminescence 

and a distinctive absorption spectrum.

aterial or laws within a stone ma% be present as inclusions. he gem ma% occur in

certain locations, called the "occurrence."

[edit] Value of gemstones

Jewelr% made with amber 

he diamond is a gemstone which has its value determined in a dierent wa% than most

or even all other gemstones. raditionall% the diamond was valued mostl% or its ph%sical properties such as hardness and brilliance, not unlike an% other (colored) gemstone, and

since a diamond was not particularl% rare, &3, other (colored) gemstones such as asapphire or a rub% were valued higher than a diamond or a long time. lthough the large

diamond inds in outh rica created an even larger suppl% o diamonds, its trade in the

30th centur% also became strongl% regulated b% a single organi+ation: >e Aeers. &5. Aoththeir monopol% o the market and their continuous marketing campaign in the last 60*96

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%ears have greatl% inluenced the perceived value o a diamond, unlike that o an% other

(colored) gemstone.

he remainder o this article deals with colored gemstones, see the diamonds article or

inormation on diamonds.

colored gemstone is pri+ed especiall% or its great beaut%, rarit% or aesthetics. lthoughcolor pla%s a ver% important role in determining the value o a gemstone, man% other

actors inluence its price as well such as market suppl%, rarit% (-ed Aer%l), popularit% o

a stone and market mechanisms.

Bh%sical characteristics that make a colored stone valuable are color, clarit% to a lesser

e8tent (emeralds will alwa%s have a number o inclusions), cut, unusual optical

 phenomena within the stone such as color +oning, and asteria (star eects). he Greeksor e8ample greatl% valued asteria in gemstones, which were regarded as a powerul love

charm, and ellen o ro% was known to have worn star*corundum. &

actor in determining the value o a gemstone is called water . Water  is an archaic termthat reers to the combination o color and transparenc% in gemstonesC used

hierarchicall%: irst water (gem o the inest water), second water, third water, b%ewater.&6

istoricall% gemstones were classiied into precious stones and semi-precious stones.

Aecause such a deinition can change over time and var% with culture, it has alwa%s been

a diicult matter to determine what constitutes precious stones. &1

side rom the diamond, the rub%, sapphire, emerald, pearl (strictl% speaking not a

gemstone) and opal &1 have also been considered to be precious. Dp to the discoveries o

 bulk ameth%st in Ara+il in the '<th centur%, ameth%st was considered a precious stone aswell, going back to ancient Greece. =ven in the last centur% certain stones such as

a@uamarine, peridot and catEs e%e have been popular and hence been regarded as

 precious. !owada%s such a distinction is no longer made b% the trade. &6 an% gemstones are used

in even the most e8pensive $ewelr%, depending on the brand name o the designer, ashion

trends, market suppl%, treatments etc. !evertheless, diamonds, rubies, sapphires andemeralds still have a reputation that e8ceeds those o other gemstones.

-are or unusual gemstones, generall% meant to include those gemstones which occur so

inre@uentl% in gem @ualit% that the% are scarcel% known e8cept to connoisseurs, includeandalusite, a8inite, cassiterite, clinohumite and bi8bite.

Gems prices can luctuate heavil% (such as those o tan+anite over the %ears) or can be@uite stable (such as those o diamonds). n general per carat prices o larger stones are

higher than those o smaller stones, but popularit% o certain si+es o stone can aect prices. %picall% prices can range rom 6D>/carat or a normal ameth%st to 30,000*

60,000D> or a collectorEs three carat pidgeon*blood almost "perect" rub%.

[edit] Gradingn the last two decades there has been a prolieration o certiication, not onl% or

diamonds but or gemstones as well. here are ive &6 ma$or laboratories which grade and

 provide reports on gemstones.

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• Gemological nstitute o merica (G)

• merican Gemological ociet% (G) is not as widel% recogni+ed nor as old as

the G but has a high reputation.

• merican Gem rade aborator% which is part o the merican Gem rade

ssociation (G) the largest trade organi+ation o $ewelers and dealers ocolored stones

• merican Gemological aboratories (G) which was recentl% taken over b%

"2ollectorEs Dniverse" a !>H listed compan% which speciali+es in

certiication o man% collectables such as coins and stamps

• =uropean Gemological aborator% (=G).

=ach laborator% has its own methodolog% to evaluate gemstones. 2onse@uentl% a stone

can be called "pink" b% one lab while another lab calls it "Badparadscha". ?ne lab canconclude a stone is untreated, while another lab concludes that it is heat treated. &6 

2ountr% o origin has sometimes been diicult to ind agreement on due to the constant

discover% o new locations. oreover determining a "countr% o origin" is much morediicult than determining other aspects o a gem (such as cut, clarit% etc.) &9

Gem dealers are aware o the dierences between gem laboratories and will make use o

the discrepancies to obtain the best possible certiicate &6. ?ne such e8ample is to makeuse o the dierences in countr% o origin: a sapphire rom Iashmir (celebrated or its

cornlower blue color) commands our times the price o the same stone rom ri anka

and twice the price as a similar stone rom Aurma. &;

=namelled gold, ameth%st and pearl pendant, about ';;0, Bas@uale !ovissimo,, born'; * died '<' 4 useum number .51*'<3;

[edit] Cutting and polishing

ew gemstones are used as gems in the cr%stal or other orm in which the% are ound.ost however, are cut and polished or usage as gemstones. he two main classiications

are stones cut as smooth, dome shaped stones called cabochons, and stones which are cutwith a aceting machine b% polishing small lat windows called acets at regular intervals

at e8act angles.

tones which are opa@ue such as opal, tur@uoise, variscite, etc. are commonl% cut as

cabochons. hese gems are designed to show the stoneEs color or surace properties as in

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opal and star sapphires. Grinding wheels and polishing agents are used to grind, shape

and polish the smooth dome shape o the stones.&<

Gems which are transparent are normall% aceted, a method which shows the optical

 properties o the stoneKs interior to its best advantage b% ma8imi+ing relected light which

is perceived b% the viewer as sparkle. here are man% commonl% used shapes or aceted

stones. he acets must be cut at the proper angles, which varies depending on the optical properties o the gem. the angles are too steep or too shallow, the light will pass

through and not be relected back toward the viewer. pecial e@uipment, a aceting

machine, is used to hold the stone onto a lat lap or cutting and polishing the lat acets.&'0 -arel%, some cutters use special curved laps to cut and polish curved acets.

[edit] Gemstone color2olor is the most obvious and attractive eature o gemstones. he color o an% material

is due to the nature o light itsel. >a%light, oten called white light, is actuall% a mi8ture

o dierent colors o light. 7hen light passes through a material, some o the light ma% be absorbed, while the rest passes through. he part that is not absorbed reaches the e%e

as white light minus the absorbed colors. rub% appears red because it absorbs all theother colors o white light * blue, %ellow, green, etc. * e8cept red.

he same material can e8hibit dierent colors. For e8ample rub% and sapphire have the

same chemical composition (both are corundum) but e8hibit dierent colors. =ven the

same gemstone can occur in man% dierent colors: sapphires show dierent shades o blue and pink and "anc% sapphires" e8hibit a whole range o other colors rom %ellow to

orange*pink, the latter called "Badparadscha sapphire".

his dierence in color is based on the atomic structure o the stone. lthough thedierent stones ormall% have the same chemical composition, the% are not e8actl% the

same. =ver% now and then an atom is replaced b% a completel% dierent atom (and this

could be as ew as one in a million atoms). hese so called impurities are suicient toabsorb certain colors and leave the other colors unaected.

s an e8ample: ber%l, which is colorless in its pure mineral orm, becomes emerald with

chromium impurities. %ou add manganese instead o chromium, ber%l becomes pinkmorganite. 7ith iron, it becomes a@uamarine.

ome gemstone treatments make use o the act that these impurities can be

"manipulated", thus changing the color o the gem.

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[edit] Treatments applied to gemstones

reble cle with gemstones

Gemstones are oten treated to enhance the color or clarit% o the stone. >epending on the

t%pe and e8tent o treatment, the% can aect the value o the stone. ome treatments areused widel% because the resulting gem is stable, while others are not accepted most

commonl% because the gem color is unstable and ma% revert to the original tone.&''

[edit] Heat

eat can improve gemstone color or clarit%. ost citrine is made b% heating ameth%st,and partial heating with a strong gradient results in ametrine * a stone partl% ameth%st and

 partl% citrine. uch a@uamarine is heat treated to remove %ellow tones, change the green

color into the more desirable blue or enhance its e8isting blue color to a purer blue. &'3

 !earl% all tan+anite is heated at low temperatures to remove brown undertones and give a

more desirable blue/purple color. considerable portion o all sapphire and rub% is

treated with a variet% o heat treatments to improve both color and clarit%.

7hen $ewelr% containing diamonds is heated(or repairs) the diamond should be

 protected with boracic acidC otherwise it could be burned on the surace or even burnedcompletel% up. 7hen $ewelr% containing sapphires or rubies is heated(or repairs) itshould not be coated with boracic acid or an% other substance, as this can etch the

suraceC it does not have to be "protected" like a diamond.

[edit] Radiation

ost blue topa+, both the lighter and the darker blue shades such as "ondon" blue, has been irradiated to change the color rom white to blue. ome improperl% handled gems

which do not pass through normal legal channels ma% have a slight residual radiation,

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though strong re@uirements on imported stones are in place to ensure public saet%. ost

greened @uart+ (?ro 4erde) is also irradiated to achieve the %ellow*green color.

[edit] Waxing/oiling

=meralds containing natural issures are sometimes illed with wa8 or oil to disguise

them. his wa8 or oil is also colored to make the emerald appear o better color as well as

clarit%. ur@uoise is also commonl% treated in a similar manner.

[edit] Fracture Filling

Fracture illing has been in use with dierent gemstones such as diamonds, emeralds and

sapphires. ore recentl% (in 3001) "Glass Filled -ubies" received a lot o publicit%.

-ubies over '0 carat (3 g), particularl% sold in the sian market with large ractures were

illed with lead glass, thus dramaticall% improving the appearance (o larger rubies in particular). uch treatments are airl% eas% to detect.

[edit] !nthetic and artificial gemstonesome gemstones are manuactured to imitate other gemstones. For e8ample, cubic

+irconia is a s%nthetic diamond simulant composed o +irconium o8ide. he imitations

cop% the look and color o the real stone but possess neither their chemical nor ph%sicalcharacteristics. owever, true s%nthetic gemstones are not necessaril% imitation. For

e8ample, diamonds, rub%, sapphires and emeralds have been manuactured in labs to

 possess ver% nearl% identical chemical and ph%sical characteristics to the naturall%occurring variet%. %nthetic corundums, including rub% and sapphire, are ver% common

and the% cost onl% a raction o the natural stones. maller  s%nthetic diamonds have been

manuactured in large @uantities as industrial abrasives. arger  s%nthetic diamonds ogemstone @ualit%, especiall% o the colored variet%, are also manuactured.

[edit] ee also

• ist o gemstones

• hree Jewels

• apidar%

[edit] "otes

1. # he ?8ord >ictionar% ?nline and 7ebster ?nline >ictionar%

2. # Williams, Gardner (1905). The Diamond ines o! "outh #!rica $ol.% and %%.

 &uc' ompan*. 

3.# Gregor*, Theodore (19+). -rnest ppenheimer. /!ord niversit* ress. 

4. #  &urnham, ".. (12+2). recious "tones in 3ature, #rt and 4iterature. &radlee

Whidden.  Bage 36'

5. L a b c d  e "ecrets o! the Gem Trade The onnoisseur6s Guide to recious

Gemstones -ichard 7 7ise, Arunswick ouse Bress, eno8, assachutes., 3005

D-: ecrets o the Gem rade, ?icial 7ebsite (as several chapters online)

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6. L a b hurch, #.7. (ro!essor at 8o*al #cadem* o! #rts in 4ondon) (1905).

 recious "tones considered in their scienti!ic and artistic relations. 7is aest*6s

"tationar* !!ice, W*man "ons.  2hapter ', Bage <: De!inition o! recious"tones D-: >einition o Brecious tones

7. # &-apaport report o 2 Gemstone 2onerene in >ubai

8. # &-ichard 7ise Alog on 2hristieEs sale o Badparadscha apphire

9. # ntroduction to apidar% b% Bans% >. Iraus

10. # Faceting For mateurs b% Glen and artha 4argas

11. # Gemstone =nhancement: istor%, cience and tate o the rt b% Iurt !assau

12. #  3assau, :urt (199;). Gem -nhancements. &utterworth 7eineman.