Mineral 1.0Test your knowledge of specific minerals

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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.

  

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