mineral
Corundum (Sapphire in Matrix)
Aluminum Oxide (Al2O3)
Hardness of 9 on the Mohs scale, hexagonal crystal system, vitreous to adamantine luster, uneven to conchoidal fracture, specific gravity of 4.0
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Physical properties
Hardness of 9 on the Mohs scale, hexagonal crystal system, vitreous to adamantine luster, uneven to conchoidal fracture, specific gravity of 4.0
Formation & geological history
Formed in metamorphic or igneous rocks such as marble, pegmatites, or basaltic alluvial deposits through high-pressure and high-temperature geological processes
Uses & applications
Used in high-end jewelry, industrial abrasives, watch bearings, and laser components
Geological facts
Corundum is the second hardest natural mineral on Earth, surpassed only by diamond. Gem-quality red varieties are called rubies, while all other colors are called sapphires.
Field identification & locations
Identified by its exceptional hardness, heavy weight for its size, and barrel-shaped hexagonal crystal habit. Found worldwide, particularly in Sri Lanka, Madagascar, East Africa, and parts of the USA.
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