A scale from 1 to 10 used to determine the hardness of minerals, talc being 1 and diamond being 10. It is a rough measure of the resistance of a smooth surface to scratching or abrasion, expressed in terms of a scale devised in 1812 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.