mineral

Ruby

Corundum (Al2O3 with Chromium traces)

Hardness: 9.0; Color: Red (pigeon blood to pinkish-red); Luster: Adamantine to vitreous; Crystal system: Trigonal/Hexagonal; Cleavage: None; Specific Gravity: 3.97–4.05

Hardness: 9
Color: Red (pigeon blood to pinkish-red)
Luster: Adamantine to vitreous

Identified April 16, 2026More mineral →

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Physical properties

Hardness: 9.0; Color: Red (pigeon blood to pinkish-red); Luster: Adamantine to vitreous; Crystal system: Trigonal/Hexagonal; Cleavage: None; Specific Gravity: 3.97–4.05

Formation & geological history

Formed through contact or regional metamorphism of aluminum-rich rocks or in marble formed from limestone. It requires high temperature, high pressure, and a lack of silica.

Uses & applications

Dominantly used in high-end jewelry as a gemstone. Industrial rubies (often synthetic) are used in laser technology, watch bearings, and precision instruments.

Geological facts

Ruby is one of the 'Big Four' precious stones. The red color is caused specifically by the presence of chromium; any other color of gem-quality corundum is called a sapphire.

Field identification & locations

Identified by its extreme hardness (scratches almost everything but diamond), high luster, and fluorescence under UV light. Found in Myanmar, Thailand, Sri Lanka, and Madagascar.