Moh's hardness scale compared to indentation hardness
3 calcite fingernail = 2.5 copper coin = 3
5 apatite pocket knife, glass = 5.5
7 quartz steel file
0000 1000 2000 3000 4000 5000 6000 7000 8000
*NOTE* The hardness of quartz is 7.0 not 6.0, as claimed in this linked demonstration!
- Note that indentation hardness is a quantitative measure of resistance
deformation by a mechanical point with known characteristics.
The above demonstrates how the relative hardness (Moh's) relates to the
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
Hardness also varies with direction:
- kyanite 5 vs 7
- diamond : cube faces soft,  hard !
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.