The Mohs Scale was devised by Friedrich Mohs in 1822, he was a German mineralogist. It was used as a method of comparing the hardness or scratch resistance of minerals. It has since become universally known as Mohs scale.
Other scales of hardness include Brinell’s Vicker’s, Meyer, and Rockwell. The hardness of each mineral relative to the other varies according to which type of test is performed and also the grain direction, or crystallographic orientation of the specimen to be tested.
In gemstones a higher scratch resistance is desirable since any stones softer than Quartz, or 7 on the Mohs scale, would not be a good choice for everyday wear, or to use as faceted gemstones. Particularly in rings or bracelets
Gems such as coral, turquoise, lapis lazuli, amber, opal and pearl are all beautiful but are quite soft, so extra care should be taken when wearing any of these. Often these gems can be found in jewelry as polished cabochons or beads since these do not show scratches or mark so easily.