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Color (beta) Automatic. Light. Dark. This page is always in light mode. ... Gemstones of the World revised 5th edition, 2013 by Walter Schumann ISBN 978-1454909538;
Bahia Emerald [2]; Carolina Emperor, [3] [4] 310 carats uncut, 64.8 carats cut; discovered in the United States in 2009, resides in the North Carolina Museum of Natural Sciences, Raleigh, NC, US
Improvements used include color alteration, improving transparency by dissolving rutile inclusions, healing of fractures (cracks) or even completely filling them. The most common treatment is the application of heat. Most rubies at the lower end of the market are heat treated to improve color, remove purple tinge, blue patches, and silk.
Sapphire (gem corundum of any color except red, especially blue varieties) Sard (a variety of chalcedony/quartz) Satinspar (a variety of gypsum) Selenite (a variety of gypsum) Simetite (a variety of amber) Smoky quartz (a brown or black variety of quartz) Soda niter (synonym of nitratine) Spectrolite (a variety of labradorite) Spessartite ...
Some tourmaline gems, especially pink to red colored stones, are altered by heat treatment to improve their color. Overly dark red stones can be lightened by careful heat treatment. The pink color in manganese-containing near-colorless to pale pink stones can be greatly increased by irradiation with gamma-rays or electron beams.
Besides the gemstone varieties that show a play of color, the other kinds of common opal include the milk opal, milky bluish to greenish (which can sometimes be of gemstone quality); resin opal, which is honey-yellow with a resinous luster; wood opal, which is caused by the replacement of the organic material in wood with opal; [13] menilite ...
Color grading of diamonds was performed as a step of sorting rough diamonds for sale by the London Diamond Syndicate. As the diamond trade developed, early diamond grades were introduced. Without any co-operative development, these early grading systems lacked standard nomenclature and consistency. Some early grading scales were; I, II, III; A, AA, AAA; A, B, C. Numerous terms
Jasper, an aggregate of microgranular quartz and/or cryptocrystalline chalcedony and other mineral phases, [1] [2] is an opaque, [3] impure variety of silica, usually red, yellow, brown or green in color; and rarely blue. The common red color is due to iron(III) inclusions. Jasper breaks with a smooth surface and is used for ornamentation or as ...