Mohs Scale

 

The most commonly used scale of relative hardness of minerals :

 

Diamond 10

Corundum 9

Topaz 8

Quartz 7

Feldspar 6

Apatite 5

Fluorite 4

Calcite 3

Gypsum 2

Talc 1

 

The divisions are not equal, having been chosen arbitrarily by the German mineralogist Mohs. The difference between 9 and 8 is considerably greater than between any of the lower numbers. Between 9 and 10 the difference is greater than between 9 and 8.