mineral

Corundum (Ruby Variety)

Corundum (Al2O3)

Hardness: 9 on Mohs scale; Color: Pinkish-red (Ruby); Luster: Adamantine to vitreous; Crystal structure: Trigonal/Hexagonal; Cleavage: None (has parting); Specific Gravity: 3.95–4.10

Hardness: 9 on Mohs scale
Color: Pinkish-red (Ruby)
Luster: Adamantine to vitreous

Identified April 13, 2026More mineral →

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Physical properties

Hardness: 9 on Mohs scale; Color: Pinkish-red (Ruby); Luster: Adamantine to vitreous; Crystal structure: Trigonal/Hexagonal; Cleavage: None (has parting); Specific Gravity: 3.95–4.10

Formation & geological history

Formed in aluminum-rich metamorphic rocks such as mica schists or gneisses, and certain igneous rocks like syenites. They often concentrate in alluvial deposits due to high density and hardness.

Uses & applications

Abrasives (industrial grade), watch bearings, lasers, and high-end jewelry (gem grade). Rough specimens are highly sought by mineral collectors.

Geological facts

Corundum is the second hardest natural mineral after diamond. Red corundum is called Ruby; all other colors are known as Sapphires.

Field identification & locations

Identify in the field by its distinct hexagonal barrel shape (crystal habit), extreme hardness (it will scratch glass and almost all other minerals), and high density. Commonly found in Myanmar, Sri Lanka, and parts of Madagascar.