gemstone

Ruby (varietal of Corundum)

Corundum (Al2O3:Cr)

Hardness: 9 on Mohs scale; Color: Deep red to pinkish-red caused by Chromium; Luster: Adamantine to vitreous; Crystal Structure: Trigonal/Hexagonal; Cleavage: None (has parting); Specific Gravity: 3.97-4.05

Hardness: 9 on Mohs scale
Color: Deep red to pinkish-red caused by Chromium
Luster: Adamantine to vitreous

Identified July 7, 2026More gemstone →

Explore Ruby (varietal of Corundum) in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed in high-pressure, high-temperature metamorphic environments (such as marble or mica schists) or in igneous rocks like basalt. Often found as water-worn pebbles in alluvial deposits.

Uses & applications

Primary use is in high-end jewelry; industrial-grade rubies (usually synthetic) are used for lasers, watch movements, and specialized abrasives.

Geological facts

Ruby is the red variety of corundum; all other colors are called sapphire. It is one of the four traditional 'precious' gemstones and is the birthstone for July.

Field identification & locations

Identify by extreme hardness (scratches almost everything except diamond), distinct red glow under UV light (fluorescence), and lack of cleavage. Common in Myanmar, Thailand, Sri Lanka, and Madagascar.