The Mohs Hardness Scale

 The Mohs hardness scale (or the Mohs scale of mineral hardness) is used by geologists/mineralogist and gemologists the world over.

The idea is that the resistance or lack of resistance to scratching can aid in the identification of various minerals. The scale uses a different mineral with he hardest known substance known to man at the time of the scales creation, diamond, being at the top end of the scale at 10 and the softest being Talc at 1 . 

The scale was developed in 1822 by Friedrich Mohs a German Geologist and mineralogist, as a method of describing the hardness of minerals and materials in science, however the technique is believed to be much older. It was mentioned in 300BCE by Theophrastus in his treatise On Stones, and then again in 77CE by Pliny the Elder in his Naturalis Historia.