mineral
Blue Sapphire
Corundum (Al2O3 with trace Titanium and Iron)
AI-generated identification · may be incorrectHardness: 9 on the Mohs scale; Color: Deep blue; Luster: Vitreous (glass-like); Crystal structure: Trigonal/Hexagonal; Cleavage: None (has parting); Specific gravity: 3.95–4.03.
- Hardness
- 9 on the Mohs scale
- Color
- Deep blue
- Luster
- Vitreous (glass-like)
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Physical properties
Hardness: 9 on the Mohs scale; Color: Deep blue; Luster: Vitreous (glass-like); Crystal structure: Trigonal/Hexagonal; Cleavage: None (has parting); Specific gravity: 3.95–4.03.
Formation & geological history
Formed in aluminum-rich metamorphic rocks (like marble or schist) or igneous rocks (like syenite) under high pressure and temperature. Commonly found in secondary alluvial deposits (riverbeds).
Uses & applications
Primary use is in high-end jewelry. Industrial uses (synthetic) include scratch-resistant watch crystals, optical components, and electronic substrates.
Geological facts
Sapphire is the birthstone for September and the traditional gift for a 45th wedding anniversary. All non-red gem-quality corundums are called sapphires, though blue is the most famous.
Field identification & locations
Identify in the field by its extreme hardness (scratches glass and steel easily) and hex-barrel crystal shape. Look for intense blue color in river gravels near volcanic or metamorphic contacts.
