gemstone
Sapphire
Corundum (Al2O3)
Hardness of 9 on the Mohs scale, typically blue but can be various colors, adamantine to vitreous luster, hexagonal crystal system, parting instead of true cleavage, specific gravity of 3.98-4.1
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Physical properties
Hardness of 9 on the Mohs scale, typically blue but can be various colors, adamantine to vitreous luster, hexagonal crystal system, parting instead of true cleavage, specific gravity of 3.98-4.1
Formation & geological history
Formed in metamorphic or igneous rocks, particularly in aluminum-rich and silica-deficient environments such as marble, pegmatites, or alkali basalts, over millions of years
Uses & applications
Used primarily in fine jewelry, as well as industrial applications such as watch crystals, scratch-resistant windows, and semiconductor substrates
Geological facts
Sapphire is the gem-variety of corundum, and while best known for its deep blue color, 'fancy' sapphires occur in every color except red (which is classified as ruby)
Field identification & locations
Can be identified in the field by its extreme hardness, heavy feel, and characteristic barrel-shaped hexagonal crystals or water-worn pebble forms; found in places like Madagascar, Sri Lanka, Australia, and the USA
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