Rocks, Minerals & Ores
Metamorphic Rocks and Minerals
Corundum
Aluminum oxideMount San Jacinto, Riverside County, CA
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Metamorphic Rocks and Minerals
Corundum is a crystalline form of aluminum oxide (Al2O3), valued for its extreme hardness—second only to diamond on the Mohs scale. It appears in metamorphic rocks formed under high pressure and temperature. At Mount San Jacinto in Riverside County, California, corundum occurs in its natural, non-gem forms, though it shares the same composition as rubies and sapphires. Its durability and distinct crystal habit make it a fascinating specimen for both geologists and collectors.