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Mohs hardness kit, containing one specimen of each mineral on the ten-point hardness scale The Mohs scale ( / m oʊ z / MOHZ ) of mineral hardness is a qualitative ordinal scale , from 1 to 10, characterizing scratch resistance of minerals through the ability of harder material to scratch softer material.
Polyhedral representation of spinel MgAl 2 O 4. Spinel (/ s p ɪ ˈ n ɛ l, ˈ s p ɪ n əl / [7]) is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula MgAl 2 O 4 in the cubic crystal system. Its name comes from the Latin word spinella, a diminutive form of spine, in reference to its pointed crystals. [5]
Most pieces of the gem, prior to Taaffe, had been misidentified as spinel. For many years afterwards, it was known only in a few samples, and it is still one of the rarest gemstone minerals in the world. [6] Since 2002, the International Mineralogical Association-approved name for taaffeite as a mineral is magnesiotaaffeite-2N'2S.
A variety of hardness-testing methods are available, including the Vickers, Brinell, Rockwell, Meyer and Leeb tests. Although it is impossible in many cases to give an exact conversion, it is possible to give an approximate material-specific comparison table for steels .
Hercynite is a spinel of regular symmetry and normal cation distribution, but some disorder occurs in its structure. It consists of ferrous (Fe 2+ ) ions and aluminium ions (Al 3+ ); however some ferric ions (Fe 3+ ) may be located in the structure of hercynite.
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Chrysocolla exhibits a wide range of Mohs hardness ranging from 2 through 7, which is dependent on the amount of silica incorporated into the stone when it is forming. Generally, dark navy blue chrysocolla is too soft to be used in jewelry, while cyan, green, and blue-green chrysocolla can have a hardness approaching 6, similar to turquoise.