topaz (tō`păz), aluminum silicate mineral with either hydroxyl radicals or fluorine, Al2SiO4(F,OH)2, used as a gem. It is commonly colorless or some shade of pale yellow to wine-yellow; pale blue and pale green also occur, but natural red stones are uncommon. Some natural yellow stones lose their yellow coloring when heated and become permanently pink ("pinked" topaz). The stone is transparent with a vitreous luster. It has perfect cleavage on the basal pinacoid, but it is nevertheless hard and durable. The brilliant cut is commonly used. Topaz crystals, which are of the orthorhombic system, occur in highly acid igneous rocks, e.g., granites and rhyolites, and in metamorphic rocks, e.g., gneisses and schists. Important sources of topaz are in Russia, Siberia, Brazil, Australia, and Mexico and in New Hampshire, Colorado, and Utah in the United States. The name topaz is commonly but incorrectly used for various other yellow stones, e.g., for citrine quartz quartz, one of the commonest of all rock-forming minerals and one of the most important constituents of the earth's crust. Chemically, it is silicon dioxide, SiO2.
..... Click the link for more information. .
Aluminum silicate mineral, Al2SiO4(F,OH)2, that is valued as a gemstone. It is formed by fluorine-bearing vapours given off during the last stages of the crystallization of igneous rocks. Pure topaz may be colourless and, when brilliant-cut, has been mistaken for diamond. It may also be various shades of yellow, blue, or brown. Imperial topaz, with vivid reddish orange colour, from Minas Gerais, Braz., is very highly valued.
topaz
..... Click the link for more information. .
topaz
)
Topaz from Minas Gerais state, Brazil
(credit: Lee Boltin)
topaz
1. a white or colourless mineral often tinted by impurities, found in cavities in igneous rocks and in quartz veins. It is used as a gemstone. Composition: hydrated aluminium silicate. Formula: Al2SiO4(F,OH)2. Crystal structure: orthorhombic
2. oriental topaz a yellowish-brown variety of sapphire
3. false topaz another name for citrine
4. a yellowish-brown colour, as in some varieties of topaz
5. either of two South American hummingbirds, Topaza pyra and T. pella
topaz
November. [Am. Gem Symbolism: Kunz, 319–320]
See : Birthstones
How to thank TFD for its existence? Tell a friend about us, add a link to this page, add the site to iGoogle, or visit webmaster's page for free fun content.
| ?Page tools | ||
|---|---|---|
|