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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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Tuesday, October 20, 2009