Topaz
(c) 2003 Andrew Alden, licensed to About.com, Inc. (fair use policy)
Topaz, the standard mineral for hardness 8 in the Mohs scale of relative hardness, is the hardest silicate along with beryl. It is usually found in high-temperature tin-bearing veins, in granites, in gas pockets in rhyolite, and in pegmatites. Topaz is tough enough to endure the pounding of streams, where topaz pebbles can occasionally be found. It formula is Al2SiO4(F,OH)2.
Its hardness, clarity, and beauty make topaz a popular gemstone, and its well-formed crystals make topaz a favorite of mineral collectors. Most pink topazes, especially in jewelry, are heated to create that color.
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