A German mineralogist, Fredrich Mohs invented a scale of relative mineral hardness that has become known as the Mohs scale. Until this day, this scale has been a valuable tool in identifying minerals since 1812.

The 10-point scale of mineral hardness. One the Mohs scale of relative hardness, a diamond is rated as 10. This means that it is the hardest mineral known to man. Only a mineral that is the same hardness grade can scratch the mineral. Sapphires for example are graded 9 on the Moh’s scale which means that only another Sapphire or a diamond (because the diamond is harder) can scratch a Sapphire. Yet, Sapphires cannot scratch a diamond because it is softer.

Mohs 10-point scale of mineral hardness table:

Hardness (from hard to soft) Mineral
 10  Diamond
 9  Sapphire, Corundum and Ruby
 8  Emerald, Aquamarine, Topaz, Beryl and Hardened Steel
 7  Quarts, Amethyst, Citrine and Agate
 6.5  Tanzanite, Steel file, Iron Pyrite, Glass and Vitreous  Pure Silca
 6  Orthoclase, Titanium and Spectrolite
 5  Apatite
 4.5  Platinum and Iron
 4  Fluorite
 3  Calcite and Copper Coin
 2.5  Pure 24K Gold, Silver and Aluminium
 2  Gypsum
 1  Talc