gemstone

Sapphire

Corundum (Al2O3)

Hardness: 9 on the Mohs scale, Color: Various (commonly blue, but also yellow, green, pink, colorless), Luster: Vitreous to adamantine, Crystal structure: Trigonal, Cleavage: None (parting may occur), Specific gravity: 3.98-4.02

Identified August 3, 2026More gemstone →

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Physical properties

Formation & geological history

Forms in igneous rocks like basalt and syenite, or in metamorphic rocks such as marble formed through regional or contact metamorphism. Often found in alluvial deposits due to its high resistance to weathering.

Uses & applications

Used primarily in fine jewelry, watch components, scratch-resistant glass, and industrial cutting and abrasive applications.

Geological facts

Sapphire is the gem variety of corundum. While blue is the most famous color, all non-red varieties of gem-quality corundum are classified as sapphires (with red being ruby).

Field identification & locations

Identified by its exceptional hardness (scratching quartz and topaz), high density, and trigonal crystal habit. Commonly sourced from Sri Lanka, Madagascar, Australia, and parts of the United States.