Corundum
Al2O3
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Corundum is the second hardest natural mineral after diamond. Its gem varieties are ruby (red, colored by chromium) and sapphire (all other colors). Synthetic corundum is widely used as an abrasive and in laser technology.
| Crystal System | Trigonal |
| Mineral Class | 04 Oxides and Hydroxides |
| Mohs Hardness | 9.0 |
| Specific Gravity | 3.98-4.10 |
| Color | Red (ruby), blue (sapphire), various colors |
| Luster | Adamantine |
| Streak | Colorless |
| Cleavage | None |
| Fracture | Conchoidal to uneven |
| Transparency | Transparent |
| Crystal Habit | Tabular, prismatic, bipyramidal |
Mohs Hardness
Mohs Hardness: 9.0 – 9.0
1 Soft10 Hard
Crystal System
TrigonalExplore on Science FYI
Frequently Asked Questions
What is the hardness of Corundum?
Corundum has a Mohs hardness of 9.0.
What crystal system does Corundum belong to?
Corundum crystallizes in the Trigonal crystal system.
What color is Corundum?
Corundum is typically Red (ruby), blue (sapphire), various colors.
What type of luster does Corundum have?
Corundum exhibits a Adamantine luster.
What is the chemical formula of Corundum?
The chemical formula of Corundum is Al2O3.