"Diamond Hardness; the good & the bad !!"

Hardness is measured as a substance's resistance to being scratched, and only a diamond can scratch another diamond.
Diamond is the toughest substance known to man & is renowned for it.

The Mohs scale - is a scale developed in 1822 by Austrian Friedreich Mohs as a criterion for mineral identification - which can help us appreciate the density of diamond.
The scale ranks 10 minerals.
Minerals, with a higher number, can scratch those with a lower number i.e. Diamond will scratch, Corundum which has a mohs no. of 9 (that’s rubies and sapphires) which in tun will scratch Topaz which has a mohs no. of 8. This will in turn scratch Quartz which has a Mohs no. of 7.

A diamond is 58 times tougher than any other mineral on earth....Corundum is nearest to it; from which rubies and sapphires are formed.
Due to this, only a diamond can cut another diamond. Rough diamonds known as "boart" which cannot be cut or shaped in to gems are crushed in to diamond powder and used in shaping and cutting other diamonds.

Even though a diamond is protected from scratches, diamond rings should not be stored with rings with softer stones like Tanzanite or Opal as the diamond will scratch them.
As tough as it is, if a Diamond is placed in an oven at 1405 degrees Fahrenheit (763 degrees Celsius), it will vanish.....only a small amount of carbon dioxide will have been released.