Topaz occurs in a variety of shades.
Topaz is the birthstone for the month of November. While most topaz jewelry is sold in a blue shade, blue topaz is actually not commonly seen in nature. Most topaz used in jewelry today is clear topaz that has been treated by irradiation to create color. Clear, or colorless, topaz occurs most frequently, with white, yellow, amber, light pink, green, and gray occurring less often. Topaz is sometimes confused with aquamarine due to the light blue color that treated topaz often has, but chemical composition of topaz and aquamarine is completely different.
Chemical Composition, Classification, and Crystal System
The chemical composition of topaz is Al2SiO4(F,OH)2. Topaz is chemically classified as a Silicate, specifically a Nesosilicate. Topaz is a member of the Orthorhombic crystal system. Twinning is very rarely observed in topaz.
Streak, Cleavage, Specific Gravity, Index of Refraction, and Birefringence
The streak of topaz is colorless or white. Topaz has perfect basal cleavage. The specific gravity of topaz is 3.4 - 3.6. The index of refraction is 1.606 - 1.638. Topaz birefringence is weak, ranging from 0.008 to 0.011.
Hardness, Color, Luster, and Transparency
Topaz ranks at an 8 on the Mohs hardness scale. The most frequently occurring topaz color is clear or colorless, but it can also appear in light blue, yellow, orange, pink, red, or violet tones. Topaz may also appear in shades of brown, varying from light to dark, that may be tinged with green. Topaz luster is typically vitreous. Topaz normally ranges from transparent to translucent.
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