gemstone

Blue Topaz

Al2SiO4(F,OH)2

Hardness: 8.0 (Mohs scale), Color: Sky blue to Swiss blue, Luster: Vitreous, Crystal structure: Orthorhombic, Cleavage: Perfect basal (001), Specific gravity: 3.4-3.6

Hardness: 8

Identified July 9, 2026More gemstone →

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Physical properties

Hardness: 8.0 (Mohs scale), Color: Sky blue to Swiss blue, Luster: Vitreous, Crystal structure: Orthorhombic, Cleavage: Perfect basal (001), Specific gravity: 3.4-3.6

Formation & geological history

Formed in high-temperature environments such as pegmatites, granite, and rhyolite via fluorine-bearing vapors during the late stages of igneous cooling. Most blue topaz in the market is clear topaz that has been irradiated and heated.

Uses & applications

Primarily used in jewelry (rings, pendants, earrings), as a birthstone for November / December, and as a durable gemstone for collectors.

Geological facts

While blue topaz occurs in nature, it is quite rare; almost all deep blue faceted topaz is created by treating colorless material. It is the state gemstone of Texas and Utah (Topaz Mountain).

Field identification & locations

Identified by high hardness, high specific gravity, and 'slippery' feel. Distinguished from aquamarine by its higher density and from glass by its double refraction and lack of air bubbles.