gemstone
Blue Topaz
Aluminum silicate fluoride hydroxide (Al2SiO4(F,OH)2)
Hardness: 8.0 (Mohs); Color: Vivid sky blue or London blue; Luster: Vitreous; Crystal Structure: Orthorhombic; Cleavage: Perfect basal; Specific Gravity: 3.49-3.57
- Hardness
- 8
- Color
- Vivid sky blue or London blue
- Luster
- Vitreous
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Physical properties
Hardness: 8.0 (Mohs); Color: Vivid sky blue or London blue; Luster: Vitreous; Crystal Structure: Orthorhombic; Cleavage: Perfect basal; Specific Gravity: 3.49-3.57
Formation & geological history
Formed in igneous environments, typically in granite pegmatites and rhyolite or within certain hydrothermal veins. Natural blue varieties are rare; most are colorless topaz treated with irradiation and heating.
Uses & applications
Primarily used as a faceted gemstone for jewelry such as rings, necklaces, and earrings due to its hardness and clarity.
Geological facts
Topaz is the birthstone for November, though the blue variety is specifically associated with December. It is the state gemstone of Texas and Utah.
Field identification & locations
Identify by high hardness (scratches quartz), high density (it feels heavy for its size), and perfect cleavage. Common sources include Brazil, Nigeria, and Sri Lanka.
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