The Mohs Hardness Scale: Complete Guide

Friedrich Mohs developed his hardness scale in 1812, ranking 10 reference minerals from talc (1) to diamond (10). The scale is relative: each mineral can scratch those below it. Talc (1), gypsum (2), calcite (3), fluorite (4), apatite (5), orthoclase (6), quartz (7), topaz (8), corundum (9), diamond (10).

Field geologists use common objects: fingernail (2.5), copper coin (3.5), knife blade (5.5), glass (5.5), steel file (6.5). Hardness indicates bonding strength in the crystal structure..