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Gem Trivia

Gemstone Characteristics and classification

A gemstone is a mineral, rock (as in lapis lazuli) or petrified material that when cut or faceted and polished is collectible or can be used in jewellery. Others are organic, such as amber (fossilised tree resin) and jet (a form of coal). Some beautiful gemstones are too soft or too fragile to be used in jewelry, for example, single-crystal rhodochrosite, but are exhibited in museums and are sought by collectors of mineral or crystal specimens.Gemstones are described and differentiated by gemmologists by certain technical specifications. First, what is it made of, its chemical composition. Diamonds for example are made of carbon (C), rubies of aluminium oxide (Al₂O₃). Next, many gems are crystals which are classified by crystal system such as cubic or trigonal or monoclinic. Another term used is habit, the form the gem is usually found in, for example diamonds which have a cubic crystal system are often found as octahedrons.

Gems are classified into different groups, species and varieties. For example, ruby is the red variety of the species corundum that belongs to the spinel or hematite group. Emerald (green), aquamarine (blue), bixbite (red), goshenite (colorless), heliodor (yellow), and morganite (pink) are all varieties of the mineral species beryl.

Gems have a certain refractive index, a certain dispersion, a certain specific gravity, a certain hardness, a certain cleavage, a certain fracture, a certain luster. They may exhibit pleochroism of a sort, or double refraction to a degree and have an optic sign. They may have a certain luminescence and a distinctive absorption spectrum.

Certain material or flaws within a stone may be present as characteristic inclusions. And the gem may occur in certain locations, "occurrence." Gems from different locations may display different characteristics which may aid in identification.

This article is licensed under the "GNU Free Documentation License".  It uses material from the Wikipedia article "Gemstones".