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Topaz is a silicate mineral of aluminium and fluorine with the chemical formula Al2SiO4(F,OH)2. Topaz crystallizes in the orthorhombic system, and its crystals are mostly prismatic terminated by pyramidal and other faces. ==Color and varieties== Pure topaz is colorless and transparent but is usually tinted by impurities; typical topaz is wine red, yellow, pale gray, reddish-orange, or blue brown. It can also be white, pale green, blue, gold, pink (rare), reddish-yellow or opaque to transparent/translucent. Orange topaz, also known as precious topaz, is the traditional November birthstone, the symbol of friendship, and the state gemstone of the US state of Utah.〔(Utah State Gem – Topaz ). Pioneer.utah.gov (2010-06-16). Retrieved on 2011-10-29.〕 Imperial topaz is yellow, pink (rare, if natural) or pink-orange. Brazilian Imperial Topaz can often have a bright yellow to deep golden brown hue, sometimes even violet. Many brown or pale topazes are treated to make them bright yellow, gold, pink or violet colored. Some imperial topaz stones can fade on exposure to sunlight for an extended period of time.〔(Imperial Topaz ), Natural History Museum of Los Angeles County〕〔(Gemstones & Gemology – Topaz ), Emporia State University〕 Blue topaz is the state gemstone of the US state of Texas.〔(State Gem – Texas Blue Topaz. State Gemstone Cut – Lone Star Cut ). state.tx.us〕 Naturally occurring blue topaz is quite rare. Typically, colorless, gray or pale yellow and blue material is heat treated and irradiated to produce a more desired darker blue.〔 Mystic topaz is colorless topaz which has been artificially coated giving it the desired rainbow effect.〔(Mystic Topaz, Consumer Information ). Farlang.com (2008-10-30). Retrieved on 2011-10-29.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Topaz」の詳細全文を読む スポンサード リンク
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