Mohs scale of mineral hardness
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Mohs' scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer. It was created, in 1812, by the German mineralogist Friedrich Mohs and is one of several definitions of hardness in materials science.
Mohs based the scale on ten readily available minerals. Materials are characterised against the scale by finding the hardest material that they can scratch.
The table below shows comparison with absolute hardness measures by a sclerometer. Mohs' is a purely ordinal scale with, for example, corundum being twice as hard as topaz, but diamond, almost four times as hard as corundum.
| Hardness | Mineral | Absolute Hardness |
|---|---|---|
| 1 | Talc (Mg3Si4O10(OH)2) | 1 |
| 2 | Gypsum (CaSO4·2H2O) | 3 |
| 3 | Calcite (CaCO3) | 9 |
| 4 | Fluorite (CaF2) | 21 |
| 5 | Apatite (Ca5(PO4)3(OH-,Cl-,F-)) | 48 |
| 6 | Orthoclase Feldspar (KAlSi3O8) | 72 |
| 7 | Quartz (SiO2) | 100 |
| 8 | Topaz (Al2SiO4(OH-,F-)2) | 200 |
| 9 | Corundum (Al2O3) | 400 |
| 10 | Diamond (C) | 1500 |
Some mnemonics traditionally taught to geology students to remember this table are "The Girls Can Flirt And Other Queer Things Can Do" or "To Get Candy From Aunt Fanny, Quit Teasing Cousin Danny".
An alternative table is shown below which has been modified to incorporate additional substances that may fall in between two levels.
Source: American Federation of Mineralogical Societies: Mohs Scale of Mineral Hardness (http://www.amfed.org/t_mohs.htm)
| Hardness | Substance or Mineral |
|---|---|
| 1 | Liquid |
| 2 | Gypsum |
| 2.5 to 3 | Gold, Silver |
| 3 | Calcite, Copper penny |
| 4 | Fluorite |
| 4 to 4.5 | Platinum |
| 4 to 5 | Iron |
| 5 | Apatite |
| 6 | Orthoclase |
| 6.5 | Iron pyrite |
| 6 to 7 | Glass, Vitreous pure silica |
| 7 | Quartz |
| 7 and up | Hardened steel |
| 8 | Topaz |
| 9 | Corundum |
| 10 | Garnet |
| 11 | Fused zirconia |
| 12 | Fused alumina |
| 13 | Silicon carbide |
| 14 | Boron carbide |
| 15 | Diamond |
cs:Mohsova stupnice tvrdosti et:Mohsi astmik eo:Mohs-skalo fr:Échelle de Mohs is:Mohs kvarði nl:Hardheidsschaal van Mohs ja:モース硬度 pl:Twardość w skali Mohsa pt:Escala de Mohs sl:Mohsova trdotna lestvica sv:Mohs hårdhetsskala