The softest material on the hardness scale is talc, which registers a rating of 1. The hardness scale, known as Mohs hardness scale, was devised and named after the German mineralogist Friedrich Mohs.
One of the defining characteristics of minerals is hardness. This property pertains to the ability of a mineral to scratch another material. All minerals are compared with respect to the 10 standard minerals used by Mohs. In a scale from 1 to 10, the minerals include talc, gypsum, calcite, fluorite, apatite, orthoclase, quartz, topaz, corundum and diamond. Talc, which is primarily composed of magnesium silicate, can easily be scraped using a copper penny or fingernail. Diamond, meanwhile, is the hardest known substance that exists in nature.