mineral
Corundum (variety Ruby/Sapphire)
Aluminum Oxide (Al2O3)
AI-generated identification · may be incorrectHardness: 9 on Mohs scale. Color: Pinkish-red (hexagonal growth lines visible). Luster: Adamantine to vitreous. Crystal structure: Trigonal/Hexagonal. Cleavage: None (has rhombohedral parting). Specific gravity: 3.95-4.10.
- Hardness
- 9 on Mohs scale
- Color
- Pinkish-red (hexagonal growth lines visible)
- Luster
- Adamantine to vitreous
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Physical properties
Hardness: 9 on Mohs scale. Color: Pinkish-red (hexagonal growth lines visible). Luster: Adamantine to vitreous. Crystal structure: Trigonal/Hexagonal. Cleavage: None (has rhombohedral parting). Specific gravity: 3.95-4.10.
Formation & geological history
Formed in silica-poor environments. Primarily occurs in metamorphic rocks like marble or gneiss, and as a primary mineral in igneous rocks like syenite. Often found in alluvial placer deposits.
Uses & applications
Non-gem quality is used as an industrial abrasive (emery). Gem-quality specimens are used in high-end jewelry. Synthetic versions are used in lasers and watch bearings.
Geological facts
Corundum is the second hardest natural mineral after diamond. The presence of chromium creates the red color of rubies, while titanium and iron create blue sapphires. This specimen shows the characteristic hexagonal barrel shape common in raw corundum crystals.
Field identification & locations
Identify by its extreme hardness (will scratch almost any other mineral) and the presence of hexagonal cross-sections or 'silk' inclusions. Often found in riverbeds or mountain metamorphic complexes in regions like Madagascar, Myanmar, or North Carolina.
