Corundum mineral is an oxide.
It forms at very high
temperatures either in hot veins or deep down in mangma.
It is therefore a very
hard mineral - the second hardest after diamond on Mohs Hardness Scale.
It is an aluminium
oxide and it forms hexagonal crystals.
It has a few gemstone
varieties including ruby and sapphire.
Ruby is the red variety, while sapphire can be blue, green, yellow and