gemstone
Blue Topaz
Aluminum silicate fluoride hydroxide (Al2SiO4(F,OH)2)
Hardness: 8 (Mohs), Color: Vivid blue, Luster: Vitreous (glassy), Crystal Structure: Orthorhombic, Cleavage: Perfect basal, SG: 3.4-3.6
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Physical properties
Hardness: 8 (Mohs), Color: Vivid blue, Luster: Vitreous (glassy), Crystal Structure: Orthorhombic, Cleavage: Perfect basal, SG: 3.4-3.6
Formation & geological history
Formed in the late stages of cooling in silicic igneous rocks like granites and pegmatites, often through fluorine-bearing vapors. While naturally blue topaz is rare, most trade specimens are colorless topaz treated with irradiation and heat.
Uses & applications
Primarily used in high-end jewelry (rings, earrings, necklaces) and as a birthstone for December.
Geological facts
Topaz is the state gemstone of Texas. Most 'Swiss Blue' or 'London Blue' topaz achieves its deep color through a common and stable laboratory enhancement of natural colorless topaz.
Field identification & locations
Identify by its high hardness (it will scratch glass and quartz) and its high density (feels heavy for its size). Natural specimens are often found in Brazil, Nigeria, and Sri Lanka.
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