The Mohs hardness scale is a scale from 1 to 10 that indicates the scratch hardness of minerals. It was drawn up in 1812 by the German mineralogist Friedrich Mohs. The principle is simple: a mineral with a higher number scratches a mineral with a lower number.
The ten reference minerals
| Value | Mineral |
|---|---|
| 1 | Talc |
| 2 | Gypsum |
| 3 | Calcite |
| 4 | Fluorite |
| 5 | Apatite |
| 6 | Feldspar (orthoclase) |
| 7 | Quartz |
| 8 | Topaz |
| 9 | Corundum |
| 10 | Diamond |
The scale is relative, not linear: diamond (10) is in reality many times harder than corundum (9).
Application in construction
- Choosing natural stone — bluestone and marble (calcite, approx. 3) are softer and more scratch-prone than granite (quartz and feldspar, approx. 6-7)
- Worktops and floors — granite and quartz composite are very scratch-resistant; marble and limestone scratch more easily
- Quick field test — a fingernail has a hardness of approx. 2.5, a steel knife approx. 5.5; this gives a rough idea of how hard a stone is
Points to watch
Scratch hardness is different from fracture sensitivity: diamond is very hard but cleavable. For floors and worktops a high Mohs value is mainly favourable against everyday scratches.
Related terms
- Natural stone
- Granite
- Bluestone
- Marble
- Quartz
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