Mineralogy
"Hardness" is determined by comparison with other minerals. In the Mohs scale, a standard set of minerals are numbered in order of increasing hardness from 1 (talc) to 10 (diamond). A harder mineral will scratch a softer, so an unknown mineral can be placed in this scale by which minerals it scratches and which scratch it. A few minerals such as calcite and kyanite have a hardness that depends significantly on direction. Hardness can also be measured on an absolute scale using a sclerometer; compared to the absolute scale, the Mohs scale is nonlinear.
Leeb rebound hardness test
According to the dynamic Leeb principle, hardness value is derived from the energy loss of a defined impact body after impacting on a metal sample, similar to the Shore scleroscope. The Leeb quotient ("v","v") is taken as a measure of the energy loss by plastic deformation: the impact body rebounds faster from harder test samples than it does from softer ones, resulting in a greater value 1000×"v/v". A magnetic impact body permits the velocity to be deduced from the voltage induced by the body as it moves through the measuring coil. The quotient 1000×v/v is quoted in the Leeb rebound hardness unit HL.