Scratch hardness

Scratch hardness is the measure of how resistant a sample is to fracture or plastic (permanent) deformation due to friction from a sharp object. The principle is that an object made of a hard material will scratch an object made of a softer material. The most common test is Mohs scale, which is used in mineralogy. One tool to make this measurement is the sclerometer

http://en.wikipedia.org/wiki/Scratch_hardness#Scratch_hardness