Topaz is a semi-precious mineral on the Mohs hardness scale with a hardness value of 8. It can form large crystals. Common for greisens and granitic pegmatites. In Russia, topazs, which were called "heavyweights", have been known since the 17th century.
You can see topaz stone for sale and buy it in the Minerals of Russia online store.
General | |
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Category | Nesosilicate minerals |
Formula (repeating unit) |
Al2SiO4(F,OH)2 |
IMA symbol | Tpz |
Strunz classification | 9.AF.35 |
Crystal system | Orthorhombic |
Crystal class | Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) |
Space group | Pbnm |
Unit cell | a = 4.65 Å, b = 8.8 Å, c = 8.4 Å; Z = 4 |
Identification | |
Color | Colorless (if there are no impurities), white, blue, brown, orange, gray, yellow, yellowish brown, green, pink, reddish pink or even red |
Crystal habit | Prismatic crystal |
Twinning | Rarely on [111] |
Cleavage | [001] Perfect |
Fracture | Subconchoidal to uneven |
Mohs scale hardness | 8 (defining mineral) |
Luster | Vitreous |
Streak | White |
Diaphaneity | Transparent |
Specific gravity | 3.49–3.57 |
Optical properties | Biaxial (+) |
Refractive index | nα = 1.606–1.629 nβ = 1.609–1.631 nγ = 1.616–1.638 |
Birefringence | δ = 0.010 |
Pleochroism | Weak in thick sections X = yellow; Y = yellow, violet, reddish; Z = violet, bluish, yellow, pink |
Ultraviolet fluorescence | Short UV=golden yellow; Long UV=cream |