mineral

Ruby (varieties of Corundum)

Aluminum oxide (Al2O3) with Chromium traces

Hardness: 9.0 Mohs scale; Color: Deep red to pink-red; Luster: Vitreous; Crystal Structure: Trigonal (hexagonal); Cleavage: None (has parting); Specific gravity: 3.97-4.05

Hardness: 9
Color: Deep red to pink-red
Luster: Vitreous

Identified May 23, 2026More mineral →

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Physical properties

Hardness: 9.0 Mohs scale; Color: Deep red to pink-red; Luster: Vitreous; Crystal Structure: Trigonal (hexagonal); Cleavage: None (has parting); Specific gravity: 3.97-4.05

Formation & geological history

Formed in metamorphic rocks (schist or marble) and igneous rocks (basalt) via contact metamorphism; found in ancient gravel deposits (alluvial)

Uses & applications

Highly valued as a precious gemstone in jewelry, industrial lasers, and historically as bearings in mechanical watches

Geological facts

The red color comes from chromium; without it, the stone is a blue sapphire. Famous specimens include the Liberty Bell Ruby and the Sunrise Ruby.

Field identification & locations

Identify by intense red color, high hardness (scratches glass/most minerals), and absence of cleavage; found in Myanmar, Sri Lanka, and Thailand.

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mineral