mineral

Sapphire

Corundum (Al2O3)

Hardness: 9 on Mohs scale; Color: Deep blue; Luster: Vitreous (glassy); Crystal Structure: Hexagonal; Cleavage: None; Specific Gravity: 3.95-4.03.

Hardness: 9 on Mohs scale
Color: Deep blue
Luster: Vitreous (glassy)

Identified June 7, 2026More mineral →

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Physical properties

Hardness: 9 on Mohs scale; Color: Deep blue; Luster: Vitreous (glassy); Crystal Structure: Hexagonal; Cleavage: None; Specific Gravity: 3.95-4.03.

Formation & geological history

Formed in metamorphic rocks (schist, gneiss) or igneous rocks (basalt, syenite) under high pressure and temperature. Large crystals often concentrate in alluvial deposits.

Uses & applications

Primary use in fine jewelry; industrial applications include high-durability windows (watch crystals), semiconductor wafers, and high-performance lasers.

Geological facts

Sapphire is the second hardest natural substance on Earth after diamond. While blue is most famous, sapphires occur in every color except red (which are rubies).

Field identification & locations

Identify by its extreme hardness (will scratch glass/steel easily) and high density; common sources include Sri Lanka, Madagascar, Myanmar, and Montana, USA.