Moh's Hardness Scale

1 Talc Extremely soft, chalklike
2 Gypsum Easily scratched with fingernail
3 Calcite Difficult to scratch with fingernail
4 Fluorspar Cannot be scratched with fingernail
5 Apatite Similar in hardness to teeth
6 Feldspar Hardness suitable for jewelry use
7 Quartz Scratches glass
8 Topaz Harder than any common mineral
9 Corundum Twice as hard as Topaz
10 Diamond Hardest, four times harder than Corundum

 

Developed in 1822 by Friedrich Moh, a German mineralogist, this scale represents the relative hardness of selected minerals. Based on the premise that gem material higher on the scale will scratch lower ordered material, this scale has become the universal standard for describing 'hardness'

It should be noted that the hardness determined is not proportional. Diamond, for example, is many times harder than the next level, Corundum.