gemstone
Blue Topaz
Aluminum silicate fluoride hydroxide (Al2SiO4(F,OH)2)
AI-generated identification · may be incorrectHardness: 8 on Mohs scale; Color: Sky blue to Swiss blue; Luster: Vitreous; Crystal Structure: Orthorhombic; Cleavage: Perfect basal; Specific Gravity: 3.49-3.57
- Hardness
- 8 on Mohs scale
- Color
- Sky blue to Swiss blue
- Luster
- Vitreous
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Physical properties
Hardness: 8 on Mohs scale; Color: Sky blue to Swiss blue; Luster: Vitreous; Crystal Structure: Orthorhombic; Cleavage: Perfect basal; Specific Gravity: 3.49-3.57
Formation & geological history
Forms in late stage igneous cooling processes in pegmatites and rhyolites; also found in hydrothermal veins. Many blue specimens are naturally colorless and treated with irradiation and heat to create the blue hue.
Uses & applications
Primary use is in high-end and fashion jewelry as a faceted gemstone for rings, necklaces, and earrings; also used by mineral collectors.
Geological facts
Topaz is one of the hardest silicate minerals and is the traditional birthstone for November. The 'London Blue' variety is prized for its deep, saturated blue-gray tone.
Field identification & locations
Identify by its high transparency, high hardness (can scratch glass and quartz), and distinct orthorhombic crystal habit in raw form. Commonly found in Brazil, Sri Lanka, and Russia.
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