mineral

Ruby

Corundum (Al2O3:Cr)

Hardness: 9 on the Mohs scale. Color: Blood red to pinkish red. Luster: Vitreous to adamantine. Crystal structure: Hexagonal/Trigonal. Cleavage: None (has parting). Specific gravity: 3.97–4.05.

Hardness: 9 on the Mohs scale
Color: Blood red to pinkish red
Luster: Vitreous to adamantine

Identified June 29, 2026More mineral →

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Physical properties

Hardness: 9 on the Mohs scale. Color: Blood red to pinkish red. Luster: Vitreous to adamantine. Crystal structure: Hexagonal/Trigonal. Cleavage: None (has parting). Specific gravity: 3.97–4.05.

Formation & geological history

Formed in metamorphic rocks such as mica schists or marbles, and occasionally in igneous rocks. The red color is caused by the presence of chromium. They are formed under high temperature and pressure in the Earth's crust.

Uses & applications

Primary use is in high-end jewelry (one of the four precious stones). Also used in industrial applications like watchmaking (bearing jewels), lasers, and scientific instruments due to hardness.

Geological facts

Rubies are the red variety of the mineral corundum; sapphire is any other color of corundum. The word 'Ruby' comes from the Latin 'ruber', meaning red. The most valuable color is a deep red called 'pigeon's blood'.

Field identification & locations

Identify by its extreme hardness (scratches almost everything but diamond) and deep red color. Look for silk-like inclusions under magnification. Commonly found in Myanmar (Burma), Madagascar, Thailand, and Mozambique.