mineral

Black Sapphire

Corundum (Al2O3 with iron and titanium impurities)

Hardness: 9 on the Mohs scale; Color: Deep blackish-blue to opaque black; Luster: Vitreous to sub-adamantine; Crystal Structure: Trigonal; Cleavage: None (conchoidal fracture); Specific Gravity: 3.98-4.06

Hardness: 9 on the Mohs scale
Color: Deep blackish-blue to opaque black
Luster: Vitreous to sub-adamantine

Identified March 6, 2026More mineral →

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Physical properties

Formation & geological history

Formed in aluminum-rich metamorphic rocks (schist, gneiss) or igneous rocks (syenite, pegmatite) through high pressure and temperature; often found in alluvial deposits (placer mines) due to its high density.

Uses & applications

Primarily used in jewelry as a more affordable alternative to blue sapphire; also used for industrial abrasives and watch bearings due to high hardness.

Geological facts

While they appear solid black, many 'black' sapphires are actually extremely dark green or blue when held against a strong light source. Famous deposits include the Chanthaburi mines in Thailand.

Field identification & locations

Identify by its exceptional hardness (it will scratch glass and most other minerals) and high density. Commonly found in Thailand, Australia, Sri Lanka, and Madagascar.

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