gemstone

Red corundum (ruby rough)

Corundum, aluminum oxide (Al₂O₃); ruby is chromium-bearing red corundum

AI-generated identification · may be incorrect

Hardness 9 Mohs; typically deep red to purplish-red, vitreous to greasy luster, trigonal crystal structure, and poor/basal cleavage. The specimen appears rough and opaque-to-translucent, with surface abrasion and possible inclusions.

Identified September 5, 2026More gemstone →

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Physical properties

Formation & geological history

Forms mainly in aluminum-rich, silica-poor metamorphic rocks such as marble and gneiss, or in basaltic/gravel placers; most gem ruby is Paleozoic to Precambrian in age, depending on deposit.

Uses & applications

Transparent, strongly colored material is cut as ruby jewelry; opaque or fractured pieces are sold as mineral specimens or used as abrasive/cutting material.

Geological facts

Ruby and sapphire are the same mineral, corundum; color is produced chiefly by chromium. Asterism may occur when oriented rutile inclusions create a star effect.

Field identification & locations

Identify by exceptional hardness, red color, hexagonal/prismatic crystal habits, and resistance to scratching; confirm with refractive index, specific gravity, and spectroscopy. Common sources include Myanmar, Mozambique, Sri Lanka, Thailand, Afghanistan, and Tanzania.