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.
Vickers hardness test
If HV is expressed in kgf/mm then the tensile strength (in MPa) of the material can be approximated as ≈ HV× ≈ HV/0.3, where is a constant determined by yield strength, Poisson's ratio, work-hardening exponent and geometrical factors - usually ranging between 2 and 4.. In other words, if HV is expressed in N/mm (i.e. in MPa) then the tensile strength (in MPa) ≈ HV/3. However it should be noted this empirical law depends variably on the work-hardening behavior of the material.