Scale, devised in 1812 by the German mineralogist Friedrich Mohs, of the scratch hardness of minerals, as: 1 talc; 2 gypsum; 3 calcite; 4 fluorite; 5 apatite; 6 orthoclase; 7 quartz; 8 topaz; 9 corundum; and 10 diamond. The scale is linear up to a hardness of 9 (corundum), but then rises dramatically to 10, with diamond about 10 times harder than corundum. The scale is still used today.