mineral

Black Sapphire

Corundum (Al2O3 with inclusions of hematite or ilmenite)

Hardness: 9 on the Mohs scale. Color: Opaque black to extremely dark blue. Luster: Vitreous to sub-adamantine. Crystal structure: Hexagonal/Trigonal. Specific gravity: 3.98 - 4.06. Cleavage: None (has parting).

Hardness: 9 on the Mohs scale
Color: Opaque black to extremely dark blue
Luster: Vitreous to sub-adamantine

Identified March 6, 2026More mineral →

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Physical properties

Formation & geological history

Formed in igneous and metamorphic rocks rich in aluminum and poor in silica. Often found in basaltic deposits, pegmatites, and alluvial deposits. Most commercial specimens are millions of years old.

Uses & applications

Primarily used in jewelry (facets, cabochons, and beads). Industrially used as an abrasive due to its high hardness, or in watch bearings and scratch-resistant windows.

Geological facts

Black sapphires often contain needle-like inclusions of hematite that can cause asterism (a star effect). While less expensive than blue sapphires, they are valued for their durability and sleek look.

Field identification & locations

Found in Australia, Thailand, and Madagascar. In the field, look for high density, hexagonal crystal habit, and the ability to scratch almost any other mineral except diamond. In jewelry, it is distinctive for its heavy weight and high luster compared to black glass or onyx.

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