mineral
Rough blue-gray sapphire (possible corundum)
Corundum, Al₂O₃; sapphire is gem-quality corundum
AI-generated identification · may be incorrectLikely blue-gray, vitreous to greasy luster, with irregular fractures and no obvious cleavage; corundum has a hexagonal crystal structure and Mohs hardness 9. The photo alone cannot confirm the identification; other gray-blue minerals may look similar.
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Physical properties
Likely blue-gray, vitreous to greasy luster, with irregular fractures and no obvious cleavage; corundum has a hexagonal crystal structure and Mohs hardness 9. The photo alone cannot confirm the identification; other gray-blue minerals may look similar.
Formation & geological history
Corundum forms in aluminum-rich, silica-poor metamorphic rocks and some igneous deposits, commonly during regional metamorphism; specimens span many geological ages.
Uses & applications
Gem-quality material is cut for jewelry; opaque or fractured pieces are collected, and industrial corundum is used as an abrasive.
Geological facts
Sapphire is corundum colored by trace elements; blue hues commonly involve iron and titanium.
Field identification & locations
Check hardness and specific gravity, and have a gemologist or lab verify it—appearance alone is insufficient. Sapphire occurs in deposits in Sri Lanka, Madagascar, Australia, Myanmar, and Montana.
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