Devised by Austrian mineralogist Frederick Mohs in 1822, Mohs' Hardness is applied to non-metallic elements and minerals. In this scale, hardness is defined by how well a substance resists scratching by another substance. A scale of 1 to 10 with half-step increments is employed. Members with higher scale numbers will scratch the surface of members in equal or lower scales.
The reference minerals for the ten scales are:
||[Ca5 (PO4)3 (F, Cl, OH)]
||[Al2SiO4 (F, OH)2]
Common Mohs' testing kits consist of low cost specimens of the 10 minerals in the Mohs' scale (or 9 if the expensive diamond is absent), labeled and stored in a wooden box. Specimens are sometimes in the form of metal rods, each containing a fragment of the reference minerals at its tip.
The Mohs' Hardness for common materials are listed below:
|Since Mohs' Hardness Scale uses existing common minerals as reference measures, it is convenient to use but does not give a continuous range of measurements. For instance, diamond (10) is 140 times harder than corundum (9), whereas flourspar (4) is only marginally (~10%) harder than calcite (3). As a result, the hardness conversions from this calculator are not exact and should be used for reference purposes only.