mineral

Ruby

Corundum (Al2O3 with Chromium impurities)

Hardness: 9 on Mohs scale; Color: Pink to blood-red; Luster: Vitreous to sub-adamantine; Crystal Structure: Trigonal/Hexagonal; Cleavage: None (has parting); Specific Gravity: 3.97–4.05

Hardness: 9 on Mohs scale
Color: Pink to blood-red
Luster: Vitreous to sub-adamantine

Identified March 13, 2026More mineral →

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Physical properties

Hardness: 9 on Mohs scale; Color: Pink to blood-red; Luster: Vitreous to sub-adamantine; Crystal Structure: Trigonal/Hexagonal; Cleavage: None (has parting); Specific Gravity: 3.97–4.05

Formation & geological history

Formed through regional or contact metamorphism of aluminum-rich rocks like marble or gneiss. Most high-quality specimens date from various geological eras, notably the Tertiary period in South Asia.

Uses & applications

Primary use is in high-end jewelry (faceted gemstones); also used in laser technology, high-precision watchmaking (jewel bearings), and scientific instruments due to extreme hardness.

Geological facts

Rubies are the most valuable variety of the corundum mineral species; if a corundum is any color other than red, it is classified as a sapphire. The red color is caused specifically by the presence of chromium.

Field identification & locations

Identify in the field by high hardness (will scratch almost everything except diamond), red streak-like hue, and high density. Found commonly in Myanmar (Burma), Sri Lanka, Madagascar, and Thailand. Quality is determined by the '4 Cs' and the depth of the 'pigeon blood' red color.