mineral
Sapphire in a ring
Corundum (Al2O3)
AI-generated identification · may be incorrectHardness: 9 on the Mohs scale; Color: Deep blue to near-black; Luster: Vitreous; Crystal Structure: Trigonal/Hexagonal; Cleavage: None; Specific Gravity: 3.95-4.03
- Hardness
- 9 on the Mohs scale
- Color
- Deep blue to near-black
- Luster
- Vitreous
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Physical properties
Hardness: 9 on the Mohs scale; Color: Deep blue to near-black; Luster: Vitreous; Crystal Structure: Trigonal/Hexagonal; Cleavage: None; Specific Gravity: 3.95-4.03
Formation & geological history
Formed in aluminum-rich igneous and metamorphic environments, specifically pegmatites, basalt, or marble. Most high-quality sapphires are millions of years old.
Uses & applications
Primary use is in high-end jewelry; industrial-grade corundum is used for abrasives, watch crystals, and high-pressure windows.
Geological facts
Sapphire is a variety of the mineral corundum. While it is famous for blue, it can occur in every color except red (which is classified as ruby).
Field identification & locations
Identification in the field usually involves its extreme hardness (cannot be scratched by steel or quartz) and high density; common in alluvial deposits in Sri Lanka, Madagascar, and Thailand.
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