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The Mohs Hardness Scale

Hardness of minerals may be tested by scratching one mineral with another. The harder mineral scratches the softer one, and mineralogists use a scale of hardness based on this principle. Friedrich Mohs, a German mineralogist, invented the scale in 1822. The Mohs Hardness Scale lists 10 minerals from the softest to the hardest, from 1 to 10. The hardness of other minerals is found by determing whether they scratch, or are scratched by, the minerals in the Mohs scale. For example, galena scratches gypsum (number 2), but is scratched by calcite (number 3). Therefore, galena's hardness is 2 -- about halfway between that of gypsum and calcite. A person's fingernail has a hardness of about 2.

Mineral Hardness Common Tests
Talc 1 Scratched by a fingernail
Gypsum 2
Calcite 3 Scratched by a copper coin
Fluorite 4 Scratched by a knife blade or window glass
Apatite 5
Feldspar 6 Scratches a knife blade or window glass
Quartz 7
Topaz 8
Corundum 9
Diamond 10 Scratches all common materials

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The Robinson Library >> Mineralogy

This page was last updated on 07/07/2018.