Minerals > Hardness

Hardness

The hardness of a mineral is the relative ease or difficulty with which it can be scratched. This property can be very useful in testing the identity of specimens. When in 1802 he recognized the value of a strict knowledge of mineral hardness, German mineralogist Friedrich Mohs (1773–1839) established a scale of 1 to 10 that now bears his name. On the Mohs scale, soft minerals (including many hydrous minerals, those that contain water) have low numbers, while hard minerals have high numbers. Examples of minerals on the Mohs scale of hardness follow:


Mohs Scale

Number Property Example
1 Very easily scratched with a fingernail Talc
2 Can be scratched with a fingernail Gypsum
3 Just scratched with a copper coin Calcite
4 Easily scratched with a knife Fluorite
5 Scratched with a knife with difficulty Apatite
6 Can’t be scratched with knife; does scratch glass Orthoclase
7 Scratches glass easily Quartz
8 Scratches glass very easily Topaz
9 Cuts glass Corundum
10 Cuts glass Diamond

Photos

Calcitecobaltoan-w
Pyrrhotite2-w

All specimens from the David J. Eicher Mineral Collection; images © David J. Eicher