mineral

Ruby (set in a gold pendant)

Ruby (Variety of Corundum, Al2O3)

Hardness: 9 on Mohs scale; Color: Red (due to chromium); Luster: Vitreous; Crystal structure: Trigonal/Hexagonal; Cleavage: None (has parting); Specific gravity: 3.97–4.05

Hardness: 9 on Mohs scale
Color: Red (due to chromium)
Luster: Vitreous

Identified April 21, 2026More mineral →

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Physical properties

Hardness: 9 on Mohs scale; Color: Red (due to chromium); Luster: Vitreous; Crystal structure: Trigonal/Hexagonal; Cleavage: None (has parting); Specific gravity: 3.97–4.05

Formation & geological history

Formed in metamorphic or igneous environments, particularly in marble (metamorphosed limestone) or basalt. Major geological sources date back to the Cretaceous or Tertiary periods depending on the region.

Uses & applications

Primarily used in high-end jewelry (faceted gemstones) and historically used in the first functional lasers; industrial-grade synthetic rubies are used for watch bearings and abrasives.

Geological facts

Rubies are the red variety of the mineral corundum; any other color of corundum is called sapphire. They are the birthstone for July and represent the 40th wedding anniversary.

Field identification & locations

Identify by its extreme hardness (only diamond and moissanite can scratch it) and distinct 'pigeon-blood' red fluorescence under UV light. Commonly found in Myanmar (Burma), Mozambique, Thailand, and Sri Lanka.

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