Gem-stone or a precious stone is a highly attractive piece of mineral. But certain organic compounds are also considered as gem stones.
E.g.: Amber
After cutting and polishing gem stones are used in jewelry.
Gemstones fall into different categories because of the composition.
E.g.: Diamonds-Made of carbon
Rubies-Aluminum oxide
Many gems are crystals and classified using a crystal system
E.g.: cubic, trogon, monoclinic
Classification of gem stones
Gems are classified classified into different groups, species and varieties.
E.g.: ruby is the red variety of species corundum
Other colours of corundum - sapphire
Value of the gems
Value of a gem depends on the refractive index, dispersion, specific gravity, hardness, cleavage, fracture and luster. Value of a certain gem changes from the country to country. Coloured gem stones are prized specially for its great beauty and aesthetics.
Processing
Most of the gems are cut and polished before they fit into a particular purpose. Some gems are treated to increase their beauty and some of the non-gem stones are converted to gems by treating.
Methods of gem treating are,
Heating
Irradiation
Waxing/Oiling
Fracture filling
Some gems are synthesized artificially
E.g.: Cubic zirconia
Synthetic corundums
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