The Mohs Scale of Hardness
The resistance of a mineral to scratching is its hardness. The hardness of a mineral is a physical expression of its chemical composition and crystalline structure, which makes it one of the physical properties that are useful in the identification of minerals.
The relative hardness of minerals is determined by how easy or difficult it is to scratch them with another mineral or objects of known hardness such as knives, files, or glass. The Mohs Scale of relative hardness is based on ten common minerals that the German mineralogist Friedrich Mohs (1812)ranked in order of increasing hardness.
The relative hardness of the first nine minerals progresses irregularly from 1 to 9 in a roughly linear manner to 9, but the absolute hardness of diamond jumps by over 300% to about 42 in comparison with talc.
For reference with familiar materials, fingernails have a hardness of just over 2, copper coins about 3, steel knife blades about 5.2, window glass 5.5 to 6, and steel files 6.5.
Copyright 2004, 2005, 2006 by Richard S. Barnett, Virtual Curator of