C O R U N D U M
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CorundumAl2O3
Class: Oxide Hardness: 9 Density: 4.0 - 4.1 Streak: White Lustre: Vitreous to adamantine Habit: Well-formed crystals Colours: Any. White, gray or gray-blue, or red (ruby), blue (sapphire), yellow, green. | | Crystal System: Hexagonal Cleavage: None Fracture: Conchoidal Magnetism: None Reaction with HCl: None | Identification in hand sample: Hardness is best indicator, crystal habit is good too. Associations: Gem quality corundum comes from metamorphed limestone or dolostone (needs high Al concentrations, here presumably from detrital deposits) Industrial / ecomonic uses: Used as a gemstone. High-quality ruby can be more valuable than diamond. Corundum is also used as an abrasive in sandpaper, polishing compounds, etc. |