mineral

Rough Blue Sapphire

Corundum (Al2O3)

Hardness: 9.0 on Mohs scale; Color: Blue (due to traces of iron and titanium); Luster: Adamantine to vitreous; Crystal structure: Trigonal/Hexagonal; Cleavage: None (has parting); Specific gravity: 3.95-4.03.

Hardness: 9
Color: Blue (due to traces of iron and titanium)
Luster: Adamantine to vitreous

Identified June 11, 2026More mineral →

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Physical properties

Formation & geological history

Formed in aluminum-rich metamorphic rocks (like marble or schist) or igneous rocks (like syenite). Commonly found in alluvial deposits. Geological age spans from Precambrian to Cenozoic depending on the source.

Uses & applications

High-quality specimens are used in fine jewelry as a gemstone. Industrial-grade corundum is used for abrasives, watch bearings, and scratch-resistant windows (sapphire glass).

Geological facts

Sapphire is a variety of the mineral corundum. Any color of corundum except red (which is ruby) is classified as sapphire. The most famous sapphires come from Kashmir, Myanmar, and Sri Lanka.

Field identification & locations

Identify by its extreme hardness (will scratch almost any other mineral except diamond) and hexagonal crystal habit. Found in secondary alluvial gravels or primary metamorphic host rock. Use a loupe to check for silk or zoning.