mineral

Sapphire Rough (Corundum)

Corundum (Aluminum Oxide, Al2O3)

Hardness: 9 on Mohs scale; Color: Blue, yellow, or grayish under brown/rusty exterior; Luster: Adamantine to vitreous when clean; Crystal structure: Trigonal/Hexagonal; Specific gravity: 3.95–4.10.

Hardness: 9 on Mohs scale
Color: Blue, yellow, or grayish under brown/rusty exterior
Luster: Adamantine to vitreous when clean

Identified June 25, 2026More mineral →

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Physical properties

Hardness: 9 on Mohs scale; Color: Blue, yellow, or grayish under brown/rusty exterior; Luster: Adamantine to vitreous when clean; Crystal structure: Trigonal/Hexagonal; Specific gravity: 3.95–4.10.

Formation & geological history

Formed in metamorphic or igneous environments, particularly in marble, granulite, or syenite; often found in secondary alluvial deposits (river beds) due to high density and weather resistance.

Uses & applications

Gemstone jewelry (once cut), industrial abrasives, watch crystals, and high-durability optical components.

Geological facts

Sapphires are the hardest natural mineral after diamonds. Except for red variations (which are rubies), all colors of gem-quality corundum are called sapphires.

Field identification & locations

Identify by high density (heavy for its size), hexagonal barrel shape (if intact), and extreme hardness (will scratch glass/quartz). Common in Sri Lanka, Madagascar, Australia, and parts of East Africa.

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