MOHS hardness scale
Invented in 1812 by the German mineralogist Friedrich Mohs
The Mohs scale measures the hardness of minerals by a comparison process.
| Hardness | Mineral | Chemical composition |
| 1 | Talc, crumbly under the nail | Mg3Si4O10 (OH) 2 |
| 2 | Gypsum, scratchable with the nail | CaSO4 · 2H2O |
| 3 | Calcite, scratchable with a copper piece | CaCO3 |
| 4 | Fluorite, scratchable (easily) with a knife | CaF2 |
| 5 | Apatite, scratchable with a knife | Ca5 (PO4) 3 (OH-, Cl-, F-) |
| 6 | Orthosis, scratchable with the file, by the sand | KAlSi3O8 |
| 7 | Quartz, scratch glass | SiO2 |
| 8 | Topaz, scratched by tungsten carbide | Al2SiO4 (OH-, F-) 2 |
| 9 | Corundum, scratchable with silicon carbide | Al2O3 |
| 10 | Diamond, scratchable with another diamond | VS |