mineral

Blue Sapphire

Corundum (Al2O3 with trace amounts of iron and titanium)

Hardness: 9 on the Mohs scale; Color: Deep navy/midnight blue (in this specimen); Luster: Vitreous (glass-like); Crystal structure: Trigonal/Hexagonal; Cleavage: None (has parting); Specific gravity: 3.98 - 4.06

Hardness: 9 on the Mohs scale
Color: Deep navy/midnight blue (in this specimen)
Luster: Vitreous (glass-like)

Identified March 10, 2026More mineral →

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Physical properties

Formation & geological history

Formed in metamorphic rocks (schists, gneisses) and igneous rocks (syenites, pegmatites) under high pressure and temperature conditions. Frequently recovered from secondary alluvial (placer) deposits.

Uses & applications

Primary use is in fine jewelry (birthstone for September). Industrial uses include high-strength infrared optical components, watch crystals, and high-durability movement bearings.

Geological facts

Sapphire is the second hardest natural mineral after diamond. The blue color is specifically caused by 'intervalence charge transfer' between iron and titanium atoms within the aluminum oxide lattice.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by steel or quartz) and high refractive index. Common locations include Sri Lanka, Madagascar, Thailand, and Montana (USA). Collectors look for 'silk' inclusions or color zoning.

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