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 Mohs Hardness Scale
Symbol:  HM

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.

 Convert   HM        (suggested range: 1 ~ 10)
 HM   5   approximately* = Hardness Symbol Amount Name SuggestedRange HB (3000) 497 Brinell 10 mm Standard 3000 kgf 80~445 HB (500) >> Brinell 10 mm Standard 500 kgf 89~189 HB (Tungsten 3000) 503 Brinell 10 mm Tungsten 3000 kgf 80~620 HB (Indentation) 2.76 mm Brinell Indentation 6~2 HK 564 Knoop 97~920 HRA 77 Rockwell A-Scale 59~86 HRB >> Rockwell B-Scale 41~100 HRC 51 Rockwell C-Scale 19~69 HRD 64 Rockwell D-Scale 39~77 HRF >> Rockwell F-Scale 88~100 HR-15N 86 Rockwell Superficial 15N 69~94 HR-15T >> Rockwell Superficial 15T 77~93 HR-30N 70 Rockwell Superficial 30N 41~85 HR-30T >> Rockwell Superficial 30T 53~82 HR-45N 57 Rockwell Superficial 45N 19~76 HR-45T >> Rockwell Superficial 45T 28~71 HS 69 Shore Scleroscope 17~97 Approx. TS 1840 MPa Tensile Strength (Approx.) 390~2450 HV 535 Vickers 20~1800

 Legend << The hardness value is below the acceptable range of the particular hardness scale. >> The hardness value is above the acceptable range of the particular hardness scale. ### The hardness value is near the limit (within 15%) of the acceptable range of the particular hardness scale. * The many hardness tests listed here measure hardness under different experimental conditions (e.g. indenters made in different sizes, shapes, and materials, and applied with different loads) and reduce their data using different formulae. As a result, there is NO direct analytic conversion between hardness measures. Instead, one must correlate test results across the multiple hardness tests. This calculator is based on hardness data compiled from ASM Metals Reference Book 3rd ed, published by ASM International, and Machinery's Handbook 25th ed, published by Industrial Press. The calculator curve-fits multiple hardness data onto a common polynomial basis and then performs an analytic conversion. The accuracy of the conversion depends on the accuracy of the provided data and the resulting curve-fits, and on the valid ranges spanned by the different hardness tests. Converted hardness values should be used for comparative purposes only.