Sapphire is the blue variation of Corundum (the red version is the Ruby).  The colour of Sapphire is because of its iron and titanium content.

Corundum is the second hardest material on Earth, after Diamond.  Hard, resistant precious stone, that can also be used for industrial purposes. Its harness also depends on the location where it was found. Sapphire is a tiny little bit harder, than Ruby.

The colour of the Corundum is not homogeneous, but lighter and darker patches and layers can be found in them, sometimes it happens that the two ends of the stone have different colours.

The world's biggest Sapphire producer is in Siam, the other important location is Ceylon.

Mohs: 9.