mineral

Black Sapphire

Corundum (Al2O3)

Hardness: 9.0 on Mohs scale; Color: Intense black to deep dark blue/green; Luster: Vitreous to Adamantine; Crystal structure: Trigonal/Hexagonal; Cleavage: None (has parting); Specific gravity: 3.95-4.03

Hardness: 9
Color: Intense black to deep dark blue/green
Luster: Vitreous to Adamantine

Identified March 6, 2026More mineral →

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Physical properties

Formation & geological history

Formed through regional metamorphism of aluminum-rich rocks or in igneous environments such as syenites and pegmatites. High-pressure, high-temperature cooling of magma or fluids allows for gemstone-quality crystal growth.

Uses & applications

Predominantly used in jewelry as a durable and affordable alternative to black diamonds. Also used in industrial applications for its extreme hardness, such as in high-pressure windows and abrasives.

Geological facts

Black sapphires are often categorized as 'low-grade' because they are heavily included with hematite or magnetite, which gives them their opaque color. They are distinct from Black Star Sapphires, which exhibit asterism.

Field identification & locations

Identify in the field by its extreme hardness (cannot be scratched by steel) and lack of cleavage. Common locations include Thailand, Australia, Sri Lanka, and Madagascar. In this jewelry piece, they are chosen for their consistent dark appearance.