Mohs' Hardness Scale Material Hardness Mohs Number Mineral 1 Talc 2 Gypsum Fingernail 2.5 3 Calcite Penny 3.5 4 Fluorite 5 Apatite Glass Plate 5.5 Knife Blade 6 6 Orthoclase 7 Quartz 8 Topaz 9 Corundum 10 Diamond Figure 1.