gemstone

Likely rough sapphire (corundum)

Corundum, Al₂O₃; identification is uncertain from the photo

AI-generated identification · may be incorrect

Dark gray-green, opaque to translucent rough crystal with a dull-to-vitreous luster; corundum is trigonal and Mohs 9, but hardness and cleavage cannot be confirmed visually. The yellow-brown material along the edge may be matrix or staining.

Identified October 10, 2026More gemstone →

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Physical properties

Formation & geological history

Corundum forms in aluminum-rich, silica-poor metamorphic rocks and some igneous deposits, commonly during metamorphism; such deposits range widely in geological age.

Uses & applications

Gem-quality sapphire is cut for jewelry; opaque or included rough material is mainly collected, while industrial corundum is used as an abrasive.

Geological facts

Color varieties of gem corundum other than red are called sapphire. A photo alone cannot distinguish rough sapphire confidently from other dark minerals.

Field identification & locations

Check for a hexagonal barrel-like crystal shape and exceptionally high hardness; definitive identification requires gemological testing. Sapphire occurs in metamorphic rocks and placer deposits in regions including Sri Lanka, Madagascar, Myanmar, and Montana.