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