gemstone

Ruby

Corundum (Al2O3:Cr)

Hardness: 9 on the Mohs scale, Color: Red to purplish-red, Luster: Vitreous to adamantine, Crystal Structure: Trigonal, Cleavage: None (exhibits parting), Specific Gravity: 3.98-4.01

Identified August 3, 2026More gemstone →

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Physical properties

Hardness: 9 on the Mohs scale, Color: Red to purplish-red, Luster: Vitreous to adamantine, Crystal Structure: Trigonal, Cleavage: None (exhibits parting), Specific Gravity: 3.98-4.01

Formation & geological history

Formed in metamorphic environments like marble or gneiss, and in igneous rocks like basalt and syenite, through regional and contact metamorphism or fractional crystallization of silica-poor magmas over millions of years.

Uses & applications

Used primarily in fine jewelry, gemstone collecting, laser technology, and precision mechanical bearings.

Geological facts

Ruby is one of the traditional cardinal gemstones. Its red color is due to the presence of trace amounts of the element chromium. Large, high-quality rubies can command higher prices per carat than diamonds.

Field identification & locations

Can be identified in the field by its extreme hardness (scratching quartz), high specific gravity, distinct red fluorescence under UV light, and typical hexagonal crystal habit or granular habit in matrix.