Mohs scale of mineral hardness
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Mohs' scale of mineral hardness characterises the scratch resistance of various minerals through the ability of a harder material to scratch a softer. It was created 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 |
| Hardness | Mineral |
|---|---|
| 1 | Liquid |
| 2 | Gypsum |
| 3 | Calcite |
| 4 | Fluorite |
| 5 | Apatite |
| 6 | Orthoclase |
| 7 | Vitreous pure silica |
| 8 | Quartz |
| 9 | Topaz |
| 10 | Garnet |
| 11 | Fused zirconia |
| 12 | Fused alumina |
| 13 | Silicon carbide |
| 14 | Boron carbide |
| 15 | Diamond |