mineral

Black Sapphire (Basaltic Blue Sapphire)

Corundum (Al2O3)

Hardness: 9 on the Mohs scale. Color: Inky dark blue to black. Luster: Vitreous to sub-metallic. Crystal Structure: Hexagonal (Trigonal). Cleavage: None, but shows rhombohedral parting. Specific Gravity: 3.95 - 4.10.

Hardness: 9 on the Mohs scale
Color: Inky dark blue to black
Luster: Vitreous to sub-metallic

Identified March 8, 2026More mineral →

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Physical properties

Formation & geological history

Formed in metamorphic or igneous environments (magmatic origin in basaltic terrain). They are often found in secondary alluvial deposits after weathering out of volcanic host rocks. Often associated with Cenozoic volcanic activity.

Uses & applications

Used in gemstone jewelry (faceted or cabochons), industrial abrasives due to high hardness, and as a natural specimen for mineral collectors.

Geological facts

Sapphires are the second hardest natural material known, surpassed only by diamonds. Dark black or 'inky' blue sapphires often contain high concentrations of iron and titanium which saturate the color to the point of appearing opaque.

Field identification & locations

Identify in the field by high density (heavy for its size), extreme hardness (it will scratch glass and almost all other minerals), and a characteristic waxy or glassy luster on weathered surfaces. Frequently found in riverbeds or gravel pits in basaltic regions.

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