![]() ![]() In 1812, the mineralogist Friedrich Mohs (1773-1839) established a reference scale of ten common minerals, ranked in order of increasing hardness. A costume cocktail ring with a slightly scratched stone. The hardness of a mineral is, specifically, its "scratchability." Every mineral can be ranked based on those others minerals it can scratch. ![]() That represents the breaking of millions of atomic bonds on a microscopic scale. If the second material is harder than the first, it'll leave a furrow, or scratch. This bonding is evident in the ease with which the layers of atoms at a surface can be separated by applying pressure with a sample of another material. Hardness depends on the bonds that hold the atoms together within a crystal structure. A variety of what we gemologists consider hard substances could easily scratch it. ![]() In the world of gemology, however, glass is fairly soft. If you ask most folks, they'll say feathers are soft and glass is hard. The scientific definition of hardness is the ability to resist scratching, nothing more. The word "hardness" has a very specific scientific meaning in gemology that differs considerably from its everyday usage. Gemstone hardness is a very misunderstood property. How is that possible if diamond is the hardest gem? Jade bell, 18th century, China, 23 x 10.8 x 5.6 cm. Hit a piece of jade with a hammer, it'll ring like a bell! Hit a piece of quartz with a hammer, it'll split in two. If you hit a diamond with a hammer, it'll shatter into a dozen pieces. ![]()
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