Moh's hardness scale compared to indentation hardness

        graphite
1       talc
2       gypsum
3       calcite fingernail = 2.5 copper coin = 3
4        fluorite
5         apatite   pocket knife, glass = 5.5
6           orthoclase
7             quartz    steel file
8                   Topaz
9                               Corundum
10                                                              diamond
         0000 1000  2000  3000  4000  5000  6000  7000  8000
                       ABSOLUTE HARDNESS

• Note that indentation hardness is a quantitative measure of resistance to deformation by a mechanical point with known characteristics. The above demonstrates how the relative hardness (Moh's) relates to the absolute hardness. For example, topaz, at 2000, is twice as hard as quartz, but is four times as hard as othoclase, which has an absolute hardness of about 500. Hardness also varies with direction:
  • kyanite 5 vs 7
  • diamond : cube faces soft, [111] hard !
• Moh's hardness scale is commonly used - the minerals are easily obtained.
• It is useful to know the minerals that make up the scale and their hardness because this provides a method to rapidly distinguish crystals and allows comprarison of gem materials to minerals in the environment (e.g., sand) that might scratch them.

How is hardness testing done? Learn to test the hardness of a mineral: