mineral

Ruby (Corundum)

Aluminium oxide (Al2O3) with Chromium traces

Hardness: 9.0 (Mohs); Color: Deep pinkish-red to blood red; Luster: Vitreous to sub-adamantine; Crystal Structure: Trigonal/Hexagonal; Specific Gravity: 3.97-4.05

Hardness: 9
Color: Deep pinkish-red to blood red
Luster: Vitreous to sub-adamantine

Identified April 12, 2026More mineral →

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Physical properties

Hardness: 9.0 (Mohs); Color: Deep pinkish-red to blood red; Luster: Vitreous to sub-adamantine; Crystal Structure: Trigonal/Hexagonal; Specific Gravity: 3.97-4.05

Formation & geological history

Formed under intense heat and pressure deep within the earth, typically found in metamorphic rocks like marble or gneiss, or as alluvial 'placer' deposits in riverbeds.

Uses & applications

Used primarily in high-end jewelry (one of the four precious stones), scientific lasers, watch bearings, and precision instruments.

Geological facts

Rubies get their red color from the element chromium. A ruby with a certain 'pigeon blood' red color is the most valuable variety. It is the birthstone for July.

Field identification & locations

Identify in the field by its extreme hardness (cannot be scratched by steel or quartz) and its fluorescent glow under UV light. Often found in gold pans due to its high specific gravity.

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