mineral
Corundum
Aluminium oxide (Al2O3)
AI-generated identification · may be incorrectHardness of 9 on the Mohs scale. Colors vary including pink, red, blue, and brown, with a vitreous to adamantine luster and hexagonal crystal structure.
Identified More mineral →
Explore Corundum in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness of 9 on the Mohs scale. Colors vary including pink, red, blue, and brown, with a vitreous to adamantine luster and hexagonal crystal structure.
Formation & geological history
Forms in metamorphic and igneous rocks, such as marble, schist, and nepheline syenites, through regional or contact metamorphism.
Uses & applications
Used extensively as an abrasive, in precision instrument bearings, lasers, and as high-value gemstones like rubies and sapphires.
Geological facts
Corundum is the second hardest natural mineral on Earth, surpassed only by diamond. Gem-quality red varieties are rubies, while all other colors are called sapphires.
Field identification & locations
Identified easily by its extreme hardness and distinct barrel-shaped or tabular hexagonal crystals. Found worldwide, particularly in Sri Lanka, Madagascar, and East Africa.
