mineral

Ruby

Corundum (Al2O3 with Chromium impurities)

Hardness: 9 on the Mohs scale. Color: Deep red to pinkish-red (pigeon's blood). Luster: Vitreous to sub-adamantine. Crystal structure: Hexagonal/Trigonal. Cleavage: None (has parting). Specific gravity: 3.97–4.05.

Hardness: 9 on the Mohs scale
Color: Deep red to pinkish-red (pigeon's blood)
Luster: Vitreous to sub-adamantine

Identified April 18, 2026More mineral →

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Physical properties

Formation & geological history

Formed through regional or contact metamorphism of aluminous rocks like limestone or marble, often in environments low in silica. Often found in marble-hosted deposits or secondary alluvial deposits.

Uses & applications

Primary use is fine jewelry and gemstone collecting. Synthetic rubies are used in horology (watch bearings), lasers, and medical instruments due to their durability and optical properties.

Geological facts

Ruby is the red variety of the mineral species corundum; all other colors are known as sapphire. The most valuable rubies exhibit a fluorescent 'glow' under UV light due to the presence of chromium.

Field identification & locations

Identify by its extreme hardness (scratches almost everything except diamond), high luster, and intense red color. Commonly found in Myanmar (Burma), Mozambique, Thailand, and Sri Lanka.