The Mohs scale of gemstone / mineral hardness was created by the German mineralogist Friedrich Mohs in 1822 to measure the relative hardness of various gemstone minerals. He based it on ten minerals that were available to him at the time. Moh’s is an ordinal scale and you have to compare two minerals to decide which is harder. For example, corundum has double the hardness as topaz, but diamond is almost four times as hard as corundum.
The hardness of a gemstone is measured by finding the hardest material that the material can scratch, or the softest material that can scratch the material.
The original Mohs scale is as follows: