MOHS SCALE

Mohs scale was invented in 1812 by Friedrich Mohs, a German mineralogist. Its purpose is to measure the hardness of minerals. It has for reference ten minerals readily available. They are ranked from softest to hardest. It is an ordinal scale where one must proceed by comparison (ability of one to scratch the other).

1 Talcum powder (friable under the nail)

2 Gypsum (scratchable with fingernail)

3 Calcite (scratched with a copper coin)

4 Fluorine (easily scratched with a knife)

5 Apatite (scratchable with a knife)

6 Orthose (scratchable with file or sand)

7 Quartz (scratches the glass)

8 Topaz (scratchable by tungsten carbide)

9 Corundum (scratchable by silicon carbide)

10 Diamond (scratchable with another diamond)

Image source: Hannes Grobe