Mohs scale

A scale for classifying stones based on relative hardness, determined by the ability of harder minerals to scratch softer ones. The scale includes the following minerals, in order from softest to hardest: Mohs Index Rock1 talc 2 gypsum 3 calcite 4 fluorite 5 apatite 6 orthoclase 7 quartz 8 topaz 9 corundum 10 diamond The scale is named for mineralogist Friedrich Mohs (German, 1773-1839). Also see measurement and science and art.