Sunday, April 26, 2009
Topaz is a silicate stone of aluminium and fluorine with the chemical formula Al2SiO4(F,OH)2. It crystallizes in the orthorhombic group and its crystals are typically prismatic terminated by pyramidal and other faces, the basal pinacoid often being present. It has an easy and perfect basal cleavage, meaning that gemstones or other fine specimens have to be handled with care to avoid increasing cleavage flaws. The fracture is conchoidal to irregular. Topaz has a resistance of 8, a specific gravity of 3.4-3.6, and a vitreous luster. Pure topaz is transparent but is generally tinted by impurities; typical topaz is wine or straw-yellow. They may also be white, gray, green, blue, pink or reddish-yellow and transparent.
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