mineral

Ruby

Corundum (Al2O3 with Chromium traces)

Hardness: 9 on the Mohs scale. Color: Pinkish-red to pigeon-blood red. Luster: Vitreous to sub-adamantine. Crystal structure: Hexagonal/Trigonal. Cleavage: None (has parting). Specific gravity: 3.97-4.05.

Hardness: 9 on the Mohs scale
Color: Pinkish-red to pigeon-blood red
Luster: Vitreous to sub-adamantine

Identified March 10, 2026More mineral →

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Physical properties

Formation & geological history

Formed through regional or contact metamorphism of aluminous rocks or in igneous environments. Often found in marble-hosted deposits or alluvial gravels. Geologically, many Asian deposits range from 5 to 50 million years old, while African deposits can be over 500 million years old.

Uses & applications

Primary use is in high-end jewelry as a gemstone. Industrial uses include lasers (the first working laser used ruby), watch bearings (synthetic), and high-pressure sensors due to its extreme hardness and thermal conductivity.

Geological facts

Ruby is the birthstone for July. The presence of chromium is what gives ruby its red color and also causes many rubies to fluoresce under UV light. It is chemically identical to sapphire, which is simply any color of corundum other than red.

Field identification & locations

Identify in the field by its hexagonal bipyramidal or tabular crystal habit and its ability to scratch almost any other mineral except diamond. Common locations include Myanmar (Burma), Mozambique, Thailand, Sri Lanka, and Madagascar.