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 2½ -- about halfway between that of gypsum and calcite. A person's fingernail has a hardness of about 2.

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This page was last updated on 11/08/2017.