05-16-2009, 11:32 PM
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Stranger
Stranger
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Join Date: Jul 2008
Posts: 4
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organic gem
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The aforementioned gemstones, unless they are synthetic, usually occur in underground deposits from which they are mined. However, there are some gems that come from once living material.
Pearls are little spheres of calcium carbonate (CaCO3) that form in mollusks (invertebrate shellfish) such as oysters, usually because of some sort of irritation. They are normally white or off-white in color, but they can have bluish or pink tints, and sometimes they are dark gray. Although many pearls form naturally, pearl production has been greatly increased by the "cultured" pearl industry, which raises beds of oysters into which irritants are routinely introduced. The irritants are usually bits of mother-of-pearl, the lining that forms inside oyster shells.
Amber is fossilized tree resin that hardened over millions of years and now is valued as a gem. Baltic amber is thought to be hardened sap from pine trees. It is normally yellow-brown in color, but the shades vary from almost white to almost black. Although sometimes completely clear, amber often contains inclusions of insects or other matter, often considered desirable. Much amber is obtained along the shores of the Baltic Sea, but it is also found along the coasts of Sicily, Romania, and Myanmar.
Coral, like pearls, is calcium carbonate (CaCO3) derived from living matter. It is the outer shells of small marine animals. It occurs in many colors, from white to deep pink and red. The greatest demand is for red coral. The best coral comes from the Mediterranean Sea, along the coasts of Algeria and Tunisia.
Ivory is a bonelike material that comes from the tusks of animals (elephant, walrus, hippopotamus). It has become such a highly prized material that there are unscrupulous poachers who kill these animals in order to steal their tusks. The pale cream color of new ivory becomes darker with age and turns yellow. Ivory is brittle, but it does not peel as do its plastic substitutes.
Jet is actually just a very hard and dense kind of lignite coal. It was probably plant material millions of years ago that has become fossilized and blackened over time. It often comes from northeast England, where it is derived from fossil driftwood buried under the sea. Its primary drawback as a gemstone is that it will burn (since it is basically just highly polished coal).
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