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:

1	2	3	4	5
Talc	Gypsum	Calcite	Flourspar	Apatite
	[CaSO4· 2H2O]	[CaCO3]	[CaF2]	[Ca5 (PO4)3 (F, Cl, OH)]
6	7	8	9	10
Orthoclase	Quartz	Topaz	Corundum	Diamond
[KAlSi3O8]	[SiO2]	[Al2SiO4 (F, OH)2]	[Al2O3]	[C]

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:

Material	HM		Material	HM		Material	HM
Fingernail	2.5		Copper Penny	3		Chalk	3
Tooth Dentin	3 ~ 4		Tooth Enamel	5		Amalgam	4 ~ 5
Gold	2.5 ~ 3		Knife Blade	5.5		Glass	5.5
Pumice	6		Steel File	6.5		Floor Tile	6.5
Tungsten Carbide	9		Silicon Carbide	9 ~ 10		Boron Carbide	9 ~ 10

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.