mineral

Ruby

Corundum (Al2O3 with Chromium)

Hardness: 9.0; Color: Red (ranging from pinkish-red to deep blood-red); Luster: Vitreous to sub-adamantine; Crystal Structure: Trigonal/Hexagonal; Cleavage: None (has parting); Specific Gravity: 3.97-4.05

Hardness: 9
Color: Red (ranging from pinkish-red to deep blood-red)
Luster: Vitreous to sub-adamantine

Identified May 9, 2026More mineral →

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Physical properties

Formation & geological history

Formed in metamorphic rocks such as mica schists or marbles, and sometimes in igneous rocks like basalt. Rubies are often found in secondary alluvial deposits (river beds). Most gem-quality rubies are millions of years old.

Uses & applications

Primary use is in high-end jewelry. Industrially, synthetic rubies are used in lasers, watchmaking (bearings), and high-pressure scientific equipment.

Geological facts

The red color comes from chromium; without it, the mineral would be a Sapphire. The most prized color is called 'pigeon blood red'. Natural rubies often have tiny inclusions called 'silk' (rutile needles) which can prove they are not synthetic.

Field identification & locations

Identify in the field by its extreme hardness (scratches almost anything but diamond) and red streak. Commonly found in Myanmar (Burma), Thailand, Sri Lanka, and Madagascar. Look for the hexagonal crystal habit in raw specimens.