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gemstones

Gemstones

World of Earth Science | 2003 | Copyright

Gemstones

Gemstones are minerals or other materials that, because of certain outstanding physical properties such as color, clarity, and hardness, have aesthetic value for use in jewelry and other adornments. Of the over 3,000 different mineral varieties known, about 50 are commonly used as gemstones. In general, for a mineral to be used as a gemstone it must be beautiful when polished, cut, or faceted, and it must be hard and durable. Rarity is another characteristic that lends value to a gemstone.

Most gemstones are minerals, but gemstones are given a name based on their appearance, as opposed to the more scientifically strict names of minerals. As a result, a mineral may have a different name for its gem version. For example, sapphire and ruby, two well-known gemstones of distinctly different color, are actually the same mineral: corundum. Emerald and aquamarine are gem forms of beryl. Quartz is called amethyst if it is purple, citrine if yellow. Other gemstones are known by their mineral name such as diamond , garnet, and topaz.

Although a gemstone may have many properties that make it appealing, the beauty of a gemstone is generally a factor of its color, clarity, and luster. The color of a gem is largely due to its chemical composition. If the color is the result of elements that are an essential part of the mineral structure, it is termed idiochromatic. These minerals usually produce gems of a consistent color, such as peridot (mineral name: olivine ), which is always green. An allochromatic gem derives its color from elemental impurities that are not integral to mineral. In this case, a mineral can vary in color, based on the varying trace impurities. Corundum, for example, is white in the pure mineral state, but slight amounts of chromium and iron will produce the red color of rubies while a combination of iron and titanium will result in sapphire blue. The color variation in diamond and quartz are also due to chemical impurities.

The clarity is the degree to which a gemstone is free of visible impurities, or inclusions. Inclusions may be tiny gas bubbles trapped in the crystal, internal fractures, or microscopic specks of a differing mineral. Inclusions are a very common result of the natural formation processes of minerals and it is the exception to find a mineral free of them and is why the most valued gems are free of inclusions. Some minerals have a greater tendency to contain inclusions, such as emerald.

The luster of a gemstone is the overall appearance as light strikes it. Gemstones are valued for a luster that is very shiny and glasslike and for one that yields a high degree of internal reflections. The latter, termed adamantine , is enhanced greatly by faceting, or the grinding of regular, angled surfaces. There are numerous patterns of faceting that are designed to maximize the natural luster of a gemstone. Diamond is a prime example of how faceting brings out its natural brilliance. Chatoyancy in gemstones, commonly known as "cat's eyes" or "stars," occurs when light reflects perpendicularly from mineral channels or mineral fibers inside the gemstone. Parallel fibers will result in a cat's eye effect; when the reflecting fibers extend in different directions, a star effect will result.

Not all gemstones are minerals. Some are naturally occurring organic materials. The popular gemstone amber, for example, is fossilized tree resin. Another, pearl, is produced when an oyster attempts to isolate a foreign particle within its shell by coating it with the same material that lines its shell: mother-of-pearl. In addition, many gemstones are now synthesized and produced in large quantities in factories.

See also Industrial minerals; Minerology
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gemstones

World Encyclopedia | 2005 | Copyright

gemstones Diamond, emerald, ruby and sapphire were formerly classified as ‘precious’ stones, with others termed ‘semi-precious’. This division is usually no longer made.

Mineral

Colour

Mohs' no.

Birthstone

1 Amber (fossilized plant resin), coral (skeletal remains of microscopic warm water creatures) and pearl (secretions in molluscs, notably mussels and oysters) are organic gems

2 Blue-green beryl

3 Alexandrite ― also called cat's eye when brownish

4 Also called cornelian

5 Green beryl

Agate

Striped grey-white, blue

6.5–7.0

May

Amber1

Yellow, honey

2.0–2.5

――

Amethyst

Purple

7.0

February

Aquamarine2

Pale blue–green

7.5

March

Beryl

Green, blue, pink

7.5

――

Bloodstone

Dark green with red spots

7.0

March

Carnelian4

Green and yellow shades

8.5

August

Chrysoberyl3

Green and yellow

8.5

June

Coral1

Varies, often red

Soft

――

Diamond

Clear (pure), various colour tints

10.0

April

Emerald5

Green

7.5–8.0

May

Garnet

Red and other various colours

6.5–7.0

January

Jade

Green

6.5–7.0

――

Lapis lazuli

Azure blue

6.5–7.0

September

Moonstone

Whitish blue

6.0–6.5

June

Onyx

Various, black and white stripes

6.5–7.0

July

Opal

Milky white, black, rainbow streaks

5.5–6.5

October

Pearl1

White, pearl grey

Soft

June

Quartz

Clear

7.0

April

Rose quartz

Pink

7.0

October

Ruby

Red

9.0

July

Sapphire

Blue

9.0

September

Smoky quartz

Smoky brown, red, yellow

7.0

――

Topaz

Blue, yellow, greenish, pink, clear

8.0

November

Tourmaline

Black, blue-black, red, green

7.0–7.5

October

Turquoise

Sky blue, greenish blue-grey

6.0–7.0

December
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Gems

-Ologies and -Isms | 1986 | Copyright

177. Gems

See also 385. STONES .

cameography
the art or technique of engraving cameos.
chatoyancy
the condition or quality of changing in color or luster depending on the angle of light, especially of a gemstone that reflects a single shaft of light when cut in cabochon form. —chatoyant, adj.
dactyliography
the art of engraving on rings.
gemmary
the scientific knowledge of gems.
gemmology
the science of gemstones. Also spelled gemology. —gemmologist, n. —gemmological, adj.
glyptic
glyptology.
glyptograph
1 . an engraving on a gemstone or other small object.
2 . the stone or object engraved.
glyptography
the art of carving or engraving upon gemstones. —glyptographer, n. —glyptographic, adj.
glyptology
the science or study of carved or engraved gemstones. Also called glyptic .
lapidary
1 . one who cuts, polishes, or engraves precious stones.
2 . a cutter of gemstones, especially diamonds.
3 . the art of cutting gemstones.
4 . a connoisseur of cut gemstones and the art of their cutting. —lapidarist, n. —lapidarian, adj.
lapidist
a lapidary.
lithoglyph
1 . an engraving or carving on a gem stone.
2 . the stone thus engraved. —lithoglyphic, lithoglyptic, adj.
lithoglypher
Obsolete, an engraver of precious stones.
lithoglyptics
the art of engraving or carving precious stones. —lithoglyptic, adj.
sigillography
the art of engraving on or designing signet rings.
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gemstone

A Dictionary of Earth Sciences | 1999 | | Copyright

gemstone Naturally occurring mineral that has been artificially polished, faceted, and shaped for decorative purposes. It is normally classified as precious (e.g. diamond, ruby, and emerald) or semi-precious (e.g. garnet, zircon, and topaz). Many gemstones are hard, clear, and free from natural imperfections.
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AILSA ALLABY and MICHAEL ALLABY. "gemstone." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>.

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gemstone

The Oxford Pocket Dictionary of Current English | 2009 | Copyright

gem·stone / ˈjemˌstōn/ • n. a precious or semiprecious stone, esp. one cut, polished, and used in a piece of jewelry.

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gemstone

Oxford Dictionary of Rhymes | 2007 | Copyright

gemstone •flagstone, ragstone •Blackstone, jackstone •sandstone • capstone • hearthstone •headstone • gemstone • whetstone •hailstone • gravestone •freestone, keystone •greenstone • Wheatstone •Tinseltown • ringtone • pitchstone •millstone • whinstone • siltstone •holystone • semitone •stepping stone • coping stone •baritone • acetone • dulcitone •tritone • drystone • milestone •limestone •grindstone, rhinestone •cobblestone • gallstone • brownstone •lodestone • soapstone • duotone •microtone • bluestone • tombstone •moonstone • touchstone •bloodstone, mudstone •sunstone • ironstone • undertone •monotone • cornerstone •Silverstone • overtone •kerbstone (US curbstone) •turnstone •birthstone • flavone • endzone •cortisone • ozone

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GEMS

The Oxford Dictionary of Abbreviations | 1998 | | Copyright

GEMS (dʒɛmz) Global Environmental Monitoring System (in the UN)
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FRAN ALEXANDER , PETER BLAIR , JOHN DAINTITH , ALICE GRANDISON , VALERIE ILLINGWORTH , ELIZABETH MARTIN , ANNE STIBBS , JUDY PEARSALL , and SARA TULLOCH. "GEMS." The Oxford Dictionary of Abbreviations. 1998. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>.

FRAN ALEXANDER , PETER BLAIR , JOHN DAINTITH , ALICE GRANDISON , VALERIE ILLINGWORTH , ELIZABETH MARTIN , ANNE STIBBS , JUDY PEARSALL , and SARA TULLOCH. "GEMS." The Oxford Dictionary of Abbreviations. 1998. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1O25-GEMS.html

FRAN ALEXANDER , PETER BLAIR , JOHN DAINTITH , ALICE GRANDISON , VALERIE ILLINGWORTH , ELIZABETH MARTIN , ANNE STIBBS , JUDY PEARSALL , and SARA TULLOCH. "GEMS." The Oxford Dictionary of Abbreviations. 1998. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O25-GEMS.html

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Free newspaper and magazine articles

Gemstone enhancement disclosure.
Magazine article from: Jewelers Circular Keystone; 1/1/2005
Colored gemstone exports rise by 29.9 percent; faced with, on the one hand...
Magazine article from: Israel Diamonds; 2/1/2004
Colored gemstone collection: a tribute to industry founder: a gem exhibition...
Magazine article from: Israel Diamonds; 2/1/2005

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