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Mohs' Hardness Scale
MOHS' HARDNESS SCALE
In 1812, Friedrich Mohs developed a scale that showed the relative hardness of minerals. The hardness of a mineral could be identified by scratching a smooth surface of the mineral with an object whose hardness is already known.
|
Level | Example | Field Test |
| 1 | talc | leaves soft, greasy flakes on the fingers |
| 2 | gypsum | easily scratched by a fingernail |
| 3 | calcite | cuts easily with a nail, can be scratched by a penny |
| 4 | fluorite | scratched easily by a knife |
| 5 | apatite | can be scratched by a knife, but with difficulty |
| 6 | orthoclase | can be scratched by a steel file |
| 7 | quartz | will scratch a steel file |
| 8 | topaz | can scratch quartz |
| 9 | corundum | -- |
| 10 | diamond | --
|
Familiar objects ranked according to Mohs' Scale of Hardness:
|
| | 0.7 | graphite |
| 1.3 | asphalt |
| 2.5 | fingernail |
| 3.0 | copper penny |
| 3.5 | brass |
| 5.5-6.0 | knife blade |
| 5.5-6.0 | plate glass |
| 6.5-7.0 | steel file
|
Thanks to Anne Wallingford for this reference material.
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