The Mohs scale is a qualitative measure of the scratch resistance of minerals. It was developed by the German geologist Friedrich Mohs in 1822. On the Mohs scale, minerals are assigned a number from 1 to 10, with 1 being the softest and 10 being the hardest. The ten minerals used to define the scale are:

* Talc (1)

* Gypsum (2)

* Calcite (3)

* Fluorite (4)

* Apatite (5)

* Orthoclase (6)

* Quartz (7)

* Topaz (8)

* Corundum (9)

* Diamond (10)

Nickel is not one of the minerals used to define the Mohs scale, so it does not have an assigned number. However, nickel is a relatively hard metal, with a hardness of about 4 on the Mohs scale. This means that it is harder than talc, gypsum, and calcite, but softer than fluorite and apatite.