The Moh's Scale measures the relative hardness of various substances. It uses ten reference minerals. The hardness of a substance is determined by scratching it against a reference mineral. If it scratches that mineral, then it is of equal hardness or harder than that mineral, otherwise it is softer then that mineral. The picture below shows the minerals that are used on the Moh's Scale.

 

Diamond is ranked as number 10, the hardest substance on this scale. The softest mineral is talc. Graphite ranks between 1 and 2 on this hardness scale. The relation between the Moh's Scale and absolute hardness measured by other means is shown below: