Mosh Hardness scale
The Mohs Hardness scale serves as a convenient way to identify a mineral’s hardness, ability to resist scratching.
In 1812, a German mineralogist named Fredrich Mohs invented a so-called «scale of hardness». He selected ten standard minerals and arranged them in order of increasing hardness (1 – the softest to 10 – the hardest), in a way that each mineral would scratch the one below it on the scale, but would not not scratch the one above it.
For example, talc is the softest mineral and diamond is the hardest one.
Referring to gems, the Mohs scale ranks them on a relative scale based on their hardness. So, although corundum (ruby or sapphire) is on the 9th level, a diamond is on the 10th, and is many times harder. Only a diamond can scratch another diamond. Corundum can scratch itself, topaz (8), quartz (7), and anything softer. Topaz can scratch itself, quartz (7), and anything lower on the scale.