Tools to measure hardness of minerals, using minerals of <a href="https://en.wikipedia.org/wiki/Mohs_scale_of_mineral_hardness" class="extiw" title="en:Mohs scale of mineral hardness">Mohs' scale of hardness</a>.
Hannes Grobe
CC BY 3.0
<span class="int-own-work" lang="en">Own work</span>