Dr Helen Lang Dept of Geology Geography West Virginia University FALL 2013 GEOLOGY 284 MINERALOGY Some minerals are valued as Gems Gems are minerals that are cut and polished and used for ornamentation What properties make certain minerals valuable as gems Some Valuable Gemstones precious Mineral Name Formula Gem Name diamond C diamond beryl Be3Al2Si6O18 emerald aquamarine corundum Al2O3 ruby sapphire H 10 7 5 8 9 Uncut Diamonds Cut and polished diamonds faceted Cutting and Polishing of Gems Some gems are polished or tumbled in a cylinder with abrasive polishing compound Harder gems are ground and polished with wheels impregnated with diamonds commonly faceted with small flat faces that accentuate the light properties Softer gems are ground with a sandstone wheel commonly with a cabochon cut smooth domed top and flat bottom Diamond Cutters in Surat Ruby Sapphire Corundum Al2O3 More Gems semi precious Mineral Name opal SiO2 chrysoberyl BeAl2O4 quartz SiO2 Gem Name opal alexandrite amethyst citrine topaz topaz Al2SiO4 OH 2 garnet Ca Mg Fe Mn 3Al2Si3O12 tourmaline tourmaline turquoise turquoise hydrous CuAl Phosphate H 7 8 5 7 7 8 7 5 7 7 5 6 Opals and opalescence
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