A decimal scale of scratch hardness for materials based on ten minerals arranged in order of hardness with 1 being the softest and 10 the most resistant. These are: 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 between 1 to 9 although diamond is about ten times harder than corundum. There is a modification to this scale in which the first six minerals are the same, but continues with 7 pure silica glass; 8 quartz; 9 topaz; 10 garnet; 11 fused zircon; 12 corundum; 13 silicon carbide; 14 boron carbide; and 15 diamond. The scale was devised in 1812 by German mineralogist Friedrich Mohs (1773–1839), and is still used today.