Diamond is the hardest known mineral. It is a high-symmetry allotrope of carbon (C). It has a Mohs “scratch” hardness of 10, which makes it the hardest mineral. Mohs hardness is a rough measure of the resistance of a smooth surface to scratching or abrasion, expressed in terms of a scale devised by the German mineralogist Friedrich Mohs. The Mohs hardness of a mineral is determined by observing whether its surface is scratched by a substance of known or defined hardness. It is a qualitative ordinal scale from 1 to 10.