mineral

Ruby (Corundum)

Corundum (Aluminum Oxide with Chromium), Al2O3:Cr

Hardness: 9 on Mohs scale; Color: Pinkish-red to deep blood red; Luster: Adamantine to vitreous; Crystal Structure: Trigonal/Hexagonal; Cleavage: None (has parting); Specific Gravity: 3.97–4.05

Hardness: 9 on Mohs scale
Color: Pinkish-red to deep blood red
Luster: Adamantine to vitreous

Identified March 27, 2026More mineral →

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Physical properties

Hardness: 9 on Mohs scale; Color: Pinkish-red to deep blood red; Luster: Adamantine to vitreous; Crystal Structure: Trigonal/Hexagonal; Cleavage: None (has parting); Specific Gravity: 3.97–4.05

Formation & geological history

Formed in metamorphic rocks (schists or gneisses) or igneous rocks (alkalinity-rich syenites). They often occur in contact metamorphic zones where limestone has been altered. Most high-quality specimens are found in secondary alluvial deposits.

Uses & applications

Primarily used as a precious gemstone in jewelry. Industrial-grade corundum (synthetic or low-quality) is used as an abrasive or in laser technology (ruby lasers).

Geological facts

The red color is caused specifically by the presence of chromium. If the stone is any color other than red, it is classified as a sapphire. It is the second hardest natural mineral after diamond.

Field identification & locations

Identify by its extreme hardness (will scratch almost everything but diamond) and characteristic hexagonal crystal habit. Common locations include Myanmar (Burma), Madagascar, Sri Lanka, and Thailand. This specimen appears to be a natural, uncut crystal thumbnail.

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