Hardness One of the most useful diagnostic properties is hardness, a measure of the resistance of a mineral to abrasion or scratching. This property is determined by rubbing a mineral of unknown hardness against one of known hardness, or vice versa. A numerical value of hardness can be obtained by using the Mohs scale of hardness, which consists of 10 minerals arranged in order from 1(softest) to 10(hardest), as shown in Figure 2.15A. It should noted that the Mohs scale is a relative ranking, and it does not imply that mineral number 2, gypsum, is twice as hard