THe Mohs Hardness Scale
You may have heard the Muses talking about a stones hardness, particularly in comparison to other stones. It is not just some figurative comparison we are making, but an actual measure of hardness of the mineral that comes from the Mohs Scale of Mineral Hardness.
The Mohs Hardness scale (as it is referred to in the jewelry industry) is not a linear scale. Fluorite at 4 is not half as hard as topaz at 8 but topaz is half the hardness of corundum at 9. And diamonds are 4 times as hard as corundum even though they are right next to each other on the scale. Because of this discrepency, the Mohs Hardness scale is not used in industrial applications, purely in a gemological context. The scale also does not account for toughness or strength. An emerald has a hardness of 7.5-8, but it is not a very tough stone, due to the inclusions which naturally occur in the crystal.
You will see things like dirt and teeth listed on the scale so as to let a person know what will be able to scratch or etch a stone. Dirt can scratch opal, so make sure to take off your Opal ring when hanging out at the beach. This scale shows things like bone can scratch amber, so we suggest you don't chew on your new Amber ring if you van avoid it.