Answer: measured using the Mohs scale
Explanation:
Hardness is defined as ability of the surface to undergo resist deformation.
The degree of hardness is determined by observing the comparative ease or difficulty which which one mineral is scratched by another.
Color is the least informative property of a mineral.
Mohs scale of hardness gives a rating of 1 to talc which is categorized as most soft and rating of 10 to diamond which is categorized as most hard.