Moh's Hardness Scale: Hardness is measured by the resistance which a smooth surface offers to abrasion. The degree of hardness is determined by observing the comparative ease or difficulty with which one mineral is scratched by another. Moh's original hardness scale is represented in real numbers from 1-10, with the selection of mineral species for hardness standards based on the common availability of the mineral.

     Each step of Moh's Hardness scale represents an increase in hardness by a multiple of two, that is, gypsum is twice as hard as talc, calcite is twice as hard as gypsum, etc. This is true of all minerals except diamonds, which have a hardness four times greater than corundum.