gemstone
Blue Topaz
Aluminum silicate fluoride hydroxide, Al2SiO4(F,OH)2
Hardness: 8 on Mohs scale; Color: Swiss Blue; Luster: Vitreous; Crystal structure: Orthorhombic; Specific Gravity: 3.49-3.57; Cleavage: Perfect basal
- Hardness
- 8 on Mohs scale
- Color
- Swiss Blue
- Luster
- Vitreous
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Physical properties
Hardness: 8 on Mohs scale; Color: Swiss Blue; Luster: Vitreous; Crystal structure: Orthorhombic; Specific Gravity: 3.49-3.57; Cleavage: Perfect basal
Formation & geological history
Formed in late-stage igneous rocks like pegmatites and rhyolites through fluorine-bearing vapors. While naturally blue topaz is rare, most commercial stones are produced by irradiating and heating clear topaz.
Uses & applications
Primarily used in jewelry (rings, pendants, earrings) due to its exceptional hardness and brilliance. Also collected as mineral specimens.
Geological facts
The 'London Blue', 'Swiss Blue', and 'Sky Blue' designations refer to specific shades of enhanced topaz. It is the birthstone for December and the state gemstone of Texas.
Field identification & locations
Identify by its high hardness (scratches glass/quartz) and high density. Commonly found in Brazil, Sri Lanka, and Nigeria. Check for pleochroism and 'slippery' feel to the touch.
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