gemstone

Blue Topaz

Aluminum silicate fluoride hydroxide (Al2SiO4(F,OH)2)

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

Hardness: 8 on Mohs scale
Color: Sky blue to Swiss blue
Luster: Vitreous

Identified July 18, 2026More gemstone →

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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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