If you haven’t heard of the MOHS it stands for The Mohs scale of mineral hardness. This equates to what the minerals hardness is in resistance to scratching against another substance. On the scale 1 means the softest and 10 being the hardness.
Diamond is always at the top of the scale, being the hardest mineral.
There are 10 minerals in the MOHS scale, talc, gypsum, calcite, fluorite, apatite, feldspar, quartz, topaz, corundum, and for last and hardest, of course is the diamond.
The MOHS Scale may be irrelievant to some people though it is a useful and extremely important tool to geologists. All minerals are given a MOHS hardness number that puts them in the rank to which number relates to the crystal.