What is the Mohs Hardness Scale? Why Is it important, and how does it work? We have an insight into all these, including how to do a Mohs hardness test, Mohs hardness test kits, and much more. However, Before we go any further, you deserve to know that the correct spelling is the Mohs Hardness Scale and not Moh's or Mohs' (i.e., one with an apostrophe). The hardness scale is Mohs, named after the inventor Carl Friedrich Christian Mohs. So, an apostrophe is unnecessary.