Hardness is measured by the resistance which a smooth surface offers to
abrasion. The degree of hardness is determined by observing the comparative ease
or difficulty which which one mineral is scratched by another.
Table showing Mohs' relative hardness scale. Mohs' original hardness
values are highlighted in yellow. The selection of mineral species for hardness
standards is based on the common availability of the mineral. An interesting
observation is the fact that each Dana class (except for organic class) of
mineral is represented by at least one example.