The hardness scale was established by the German mineralogist, Friedrich Mohs. The Mohs hardness scale places ten common or well-known minerals on a scale from one to ten. One is the softest mineral and ten is the hardest. These are the minerals used in the Mohs hardness scale:
|Mohs' Hardness Scale|
To use the hardness scale, try to scratch the surface of an unknown sample with a mineral or substance from the hardness scale (these are known samples). If the unknown sample cannot be scratched by feldspar (6) but it can be scratched by quartz (7), then it's hardness is between 6 and 7. An example of a mineral that has a hardness between 6 and 7 is pyrite (6 to 6.5).
If you don't have minerals from the hardness scale on hand, here are some common objects and their hardness values:
|Common Objects and Their Hardness Values|
If an unknown sample can not be scratched by your fingernail (2.5) but it can be scratched by a penny (3.5), then it's hardness is between 2.5 and 3.5. An example of a mineral that has a hardness between 2.5 and 3.5 is calcite (3).