Read the time on the clock and learn the Mohs Scale of Hardness The Mohs’ hardness scale was developed in 1822 by Carl Friedrich Christian Mohs (a german geologist and mineralogist). This scale is a chart of relative hardness and resistance of the various minerals (1 – softest to 10 – hardest). Hardness is determined by scratching the mineral with a mineral or substance of known hardness. Made by a Geologist for Geologists. _______________________________ Note: I constantly update this application with new features and photos. Facebook - https://www.facebook.com/Geology.Toolkit