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)