mineral

Sapphire

Corundum (Al2O3)

Hardness: 9 on Mohs scale; Color: Deep blue; Luster: Vitreous to sub-adamantine; Crystal Structure: Trigonal/Hexagonal; Specific Gravity: 3.95-4.03

Hardness: 9 on Mohs scale
Color: Deep blue
Luster: Vitreous to sub-adamantine

Identified June 11, 2026More mineral →

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Physical properties

Hardness: 9 on Mohs scale; Color: Deep blue; Luster: Vitreous to sub-adamantine; Crystal Structure: Trigonal/Hexagonal; Specific Gravity: 3.95-4.03

Formation & geological history

Formed under high pressure and temperature in metamorphic rocks like marble or gneiss, and in igneous rocks like basalt. Found in alluvial deposits where it has weathered out of its host rock over millions of years.

Uses & applications

Primary use is in high-end jewelry; industrial uses include infrared optical components, high-durability windows, and watch crystals due to its extreme hardness.

Geological facts

Sapphires are the birthstone for September and represent wisdom and royalty. Red corundum is called Ruby, while all other colors are referred to as Sapphires.

Field identification & locations

Identified by its extreme hardness (scratches almost everything but diamond) and high density. Commonly found in Sri Lanka, Madagascar, Myanmar, and Australia. Natural sapphires often contain 'silk' (rutile inclusions).