Mohs Hardness Scale

Mohs hardness is measured on a scale from 1 to 10 with softer minerals designated by low numbers and harder minerals designated by high numbers. The scale was developed about 200 years ago by Friedrich Mohs.

Mohs scale number (mineral example)
1 (Talc)
2 (Gypsum)
3 (Calcite)
4 (Fluorite)
5 (Apatite)
6 (Orthoclase Feldspar)
7 (Quartz)
8 (Topaz)
9 (Corundum)
10 (Diamond)

Hardness of other common objects
Fingernail: 2.5
Copper penny: 3
Glass: 5.5

To figure out the hardness of a mineral, try to scratch it with an object of known hardness. For instance, if a fingernail cannot scratch a mystery mineral, we know it has a hardness of more than 2.5. If the mystery mineral can't scratch glass, we know it has a hardness of less than 5.5.

Last modified May 1, 2003 by Lisa Gardiner.

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