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''This article is about the mineral or gemstone, for other uses see: [[Topaz (disambiguation)]].''

[[Image:TopazUSGOV.jpg|thumb|Topaz]]
The [[mineral]] '''topaz''' is a [[silicate]] of [[aluminium]] and [[fluorine]] with the chemical formula (<nowiki>AlF</nowiki>)<sub>2</sub><nowiki>SiO</nowiki><sub>4</sub>. It is [[orthorhombic]] and its [[crystal]]s are mostly prismatic terminated by pyramidal and other faces, the basal pinacoid often being present. It has an easy and perfect basal cleavage and so [[gemstone]]s or other fine specimens should be handled with care to avoid developing cleavage flaws. The fracture is [[conchoid]]al to uneven. Topaz has a [[Mohs scale of mineral hardness|hardness]] of 8, a [[specific gravity]] of 3.4-3.6, and a vitreous lustre. Pure topaz is transparent but is usually tinted by impurities; typical topaz is wine or straw-[[yellow]]. They may also be [[white]], [[gray (color)|gray]], [[green]], [[blue]], or [[red]]dish-yellow and transparent or translucent. When heated, yellow topaz often becomes reddish-[[pink]].

Topaz is found associated with the more acid rocks of the [[granite]] and [[rhyolite]] type and may be found with [[fluorite]] and [[cassiterite]]. It can be found in the [[Ural mountains|Ural]] and [[Ilmen mountains|Ilmen]] mountains, [[Czech Republic]], [[Saxony]], [[Norway]], [[Sweden]], [[Japan]], [[Brazil]], [[Mexico]], and the [[United States]].

The name "topaz" is derived from the [[Greek language|Greek]] "to seek," which was the name of an [[island]] in the [[Red Sea]] that was difficult to find and from which a yellow stone (now believed to be a yellowish [[olivine]]) was mined in ancient times. In the [[Middle Ages]] the name topaz was used to refer to any yellow gemstone, but now the name is only properly applied to the silicate described above.

*''See also:'' [[List of minerals]]

[[Category:Gemstones]]
[[Category:Silicate minerals]]

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