Density: 4.0 - 4.1
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|
Reaction with HCl: None
Identification in hand sample:
Hardness is best indicator, crystal habit is good too.
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.