mineral

Rough Sapphire (Corundum)

Corundum (Al2O3)

Hardness: 9 on Mohs scale. Color: Greenish-blue to brownish-yellow rough hue. Luster: Vitreous to adamantine. Crystal structure: Hexagonal / Trigonal. Specific gravity: 3.98-4.06. Cleavage: None (shows parting).

Hardness: 9 on Mohs scale
Color: Greenish-blue to brownish-yellow rough hue
Luster: Vitreous to adamantine

Identified July 27, 2026More mineral →

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Physical properties

Formation & geological history

Formed in aluminum-rich and silica-poor metamorphic environments such as schists, gneisses, or contact-metamorphosed limestones, as well as in alkali igneous rocks and placer alluvial deposits.

Uses & applications

Used primarily as gemstone material for jewelry when faceted, cabbed, or collected as raw mineral specimens. Industrial corundum is used as an abrasive.

Geological facts

Corundum is the second hardest natural substance known after diamond. Sapphire refers to any gem-quality corundum variety other than red (which is ruby).

Field identification & locations

Identified by extreme hardness (scratches quartz and topaz), high density, hexagonal growth striations, and barrel-shaped crystal habits. Common locations include Madagascar, Sri Lanka, Myanmar, Australia, and Montana, USA.