Mohs' scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer. It was created by the German mineralogist Friedrich Mohs and is one of several definitions of hardness in materials science.
Mohs based the scale on ten readily available minerals. Materials are characterised against the scale by finding the hardest material that they can scratch.
The table below shows comparison with absolute hardness measures by a sclerometer. Mohs' is a purely ordinal scale with, for example, corundum being twice as hard as topaz, but diamond, almost four times as hard as corundum.
With his systematic classification of the realm of minerals, Mohs was in conflict with most of the other mineralogists of the time, due to his preference for physical attributes as the principles of classification (i.e., shape, cleavage, hardness, and specific weight), as opposed to the chemical composition of the minerals.
In 1812, Mohs was appointed Professor of Mineralogy at the Joanneum in Graz.
In 1826, Mohs was appointed Professor of Mineralogy at the University of Vienna.
Since hardness depends upon the crystallographic direction (ultimately on the strength of the bonds between atoms in a crystal), there can be variations in hardness depending upon the direction in which one measures this property.
Mohs' hardness is a measure of the relative hardness and resistance to scratching between minerals.
The scratch hardness is related to the breaking of the chemical bonds in the material, creation of microfractures on the surface, or displacing atoms (in metals) of the mineral.
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