Cryptocrystalline quartz, such as chalcedony, has “tough” tenacity. As it so happens, most gemstones would be considered “brittle.” There are a few exceptions. For gemstones, these measurements are usually given as descriptive terms. “Tenacity” measures a material’s resistance to blows. The steel of a hammer (hardness 5 or 6) won't scratch a diamond, but it can shatter a diamond. Going back to the old saying, a diamond is both hard, defined scientifically, and brittle. Kyanite and quartz, Barra de Salinas, Coronel Murta, Jequitinhonha Valley, Minas Gerais, Brazil. However, kyanite is unusual in that its hardness may vary tremendously, from 4 to 7.5, within a single crystal. Gemstone hardness may vary a bit within a species. In most cases, the hardness range reported is very small (one unit). In only one case, kyanite, does the hardness of a mineral vary very widely, even within a single crystal. The values reported on this website represent all values encountered in the literature. A hardness range is much more meaningful. However, it's really not critical whether the hardness of a mineral is 5 or 5.5. Often, a mark that looks like a scratch is actually a trail of powder left by the supposedly harder material! Fractional hardness scores, like 5.5, are reported when the literature has indicated an intermediate value. The hardness of a material may vary slightly with composition and also with its state of aggregation. Measuring gemstone hardness can be tricky. (Note: diamonds, and only diamonds, can scratch other diamonds). Corundum (9) is twice as hard as topaz (8), and diamond (10) is four times as hard as corundum. The Mohs scale starts approximately linear, but the curve climbs sharply at the high end. A diamond is much harder than corundum, even though they're only one division apart on the scale. Thus, a ruby can't scratch a sapphire and vice versa. Minerals of the same hardness won't scratch each other. I've added some examples of other familiar items to help illustrate the concept.Įach of these minerals can be scratched by the one above it and will scratch the ones below it. This scale, shown below, is called the Mohs scale of hardness. 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.
0 kommentar(er)
