Hardness:
To determine the hardness of a stone, the Mohs scale of hardness is of an everyday usage in mineralogy. 

It is made up of ten following minerals of reference:

  • 10 – Diamond (hardest)
  • 9 – Corundum ( Ruby-Sapphire )
  • 8 – Topaz
  • 7 – Quartz
  • 6 – Feldspar
  • 5 – Apatite
  • 4 – Fluorite
  • 3 – Calcite
  • 2 – Gypsum
  • 1 – Talc (softest)