Topaz: Birth Stone November
Topaz is an appreciated and valued gemstone variety of mineral aluminum fluosilicate, crystallized in the orthorhombic system.
It has a vitreous luster and may be clear, pale blue, yellow, green or red. The most valuable stones are golden-yellow, a form of topaz called imperial topaz.
It has a hardness of 8 and a specific gravity of 3.4 to 3.6. Although it is a hard stone, only two steps lower than the diamond, topaz can be broken easily because the crystal has a perfect line of cleavage.
In Russia fine specimens are found in several places in the Nerchinsk district in Siberia and at the classic occurrence at Mursinka in the Urals.
In the USA Topaz is found at Pikes Peak in Colorado and the Thomas Range in Utah. Topaz is known also from Sri Lanka and Pakistan and the classic Schneckenstein occurrence in Saxony, Germany.
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Topaz occurs in gneiss or granite associated with beryl, mica, and tourmaline and occasionally with apatite, cassiterite, and fluorite; it also occurs in certain talcose rocks, mica slate, rhyolite, and in alluvial deposits and drift.
At Ouro Preto and other localities in Minas Gerais, Brazil, very large crystals up to more then 200kg have been found.