mineral

Ruby

Corundum (Al2O3 with Chromium traces)

Hardness: 9.0 (Mohs scale); Color: Pinkish-red to deep blood red; Luster: Vitreous to sub-adamantine; Crystal structure: Trigonal/Hexagonal; Cleavage: None; Specific Gravity: 3.97-4.05

Hardness: 9
Color: Pinkish-red to deep blood red
Luster: Vitreous to sub-adamantine

Identified June 14, 2026More mineral →

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Physical properties

Hardness: 9.0 (Mohs scale); Color: Pinkish-red to deep blood red; Luster: Vitreous to sub-adamantine; Crystal structure: Trigonal/Hexagonal; Cleavage: None; Specific Gravity: 3.97-4.05

Formation & geological history

Formed primarily in marble deposits through contact metamorphism or in basaltic rocks. Created under high pressure and temperature where silica is absent and aluminum is present.

Uses & applications

Primarily used as a gemstone in high-end jewelry. Also used in industrial lasers, watch bearings, and precision instruments due to its extreme hardness and thermal conductivity.

Geological facts

The red color is caused by trace amounts of chromium. Rubies with a slight blue tint are often called 'pigeon's blood' rubies and are the most valuable. It is the birthstone for July.

Field identification & locations

Identified by its distinctive red fluorescence under UV light and its extreme hardness (second only to diamond). Look for 'silk' inclusions (rutile needles) in natural specimens. Commonly found in Myanmar, Sri Lanka, and Thailand.