mineral
Raw Sapphire / Corundum
Corundum (Al2O3 - Aluminium oxide)
Hardness 9 on Mohs scale, vitreous to adamantine luster, trigonal/hexagonal crystal system, basal parting, color ranges from greyish-blue, brownish-tan to blue, specific gravity ~4.0
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Physical properties
Hardness 9 on Mohs scale, vitreous to adamantine luster, trigonal/hexagonal crystal system, basal parting, color ranges from greyish-blue, brownish-tan to blue, specific gravity ~4.0
Formation & geological history
Formed through regional or contact metamorphism of aluminum-rich silica-poor rocks like marble and schist, or in silica-undersaturated igneous rocks like syenites and pegmatites.
Uses & applications
Cut into gemstones for high-end jewelry, used as an industrial abrasive, used in scratch-resistant optical windows, and collected as mineral specimens.
Geological facts
Corundum is the second hardest natural substance known after diamond. Non-red gem varieties of corundum are called sapphires, while red varieties are known as rubies.
Field identification & locations
Identified in the field by its extreme hardness (scratches quartz and topaz), high density, hexagonal growth striations, and characteristic barrel-like or prismatic crystal habits. Found commonly in Sri Lanka, Madagascar, Myanmar, Kashmir, Australia, and Montana, USA.
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