mineral

Ruby

Corundum (Al2O3:Cr)

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

Identified April 1, 2026More mineral →

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Physical properties

Formation & geological history

Formed in metamorphic rocks (schists or marbles) or igneous rocks (alkali basalts) under high heat and pressure, often found in alluvial deposits. They can be found in formations dating back millions of years depending on the deposit site (e.g., Cenozoic to Precambrian).

Uses & applications

Used primarily in high-end jewelry (faceted gemstones and cabochons) and specialized industrial applications such as lasers, high-precision bearings (watch jewels), and scratch-resistant windows.

Geological facts

The red color is caused by the presence of chromium. It is one of the four traditional 'precious stones' along with diamond, sapphire, and emerald. Some rubies exhibit 'asterism' (a star effect) under certain lighting conditions.

Field identification & locations

Identify by its extreme hardness (9), lack of cleavage, and red streak. In the field, look for hexagonal prismatic crystals in marble or basalt matrix. Commonly found in Myanmar (Burma), Thailand, Mozambique, and Sri Lanka.