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Friedrich Mohs, 1832
|Born||29 January 1773|
|Died||29 September 1839 (aged 66)|
|Alma mater||University of Halle|
|Known for||Mohs scale of mineral hardness|
Carl Friedrich Christian Mohs (German: [mo:s]; 29 January 1773 - 29 September 1839) was a German geologist and mineralogist. He was the creator of the Mohs scale of mineral hardness. Mohs also introduced a classification of the crystal forms in crystal systems independently of Christian Samuel Weiss.
After assuming the position of a foreman at a mine in 1801, Mohs moved in 1802 to Austria, where he was employed in trying to identify the minerals in a private collection of the banker J. F. van der Nüll. Mohs described this collection, a catalogue was printed and published. In 1812 he moved to Graz where he was employed by Archduke Johann in his newly established museum and science academy, which was subsequently divided into the Joanneum and the Graz University of Technology. In 1818 Mohs was appointed successor of his former professor at the Freiberg Mining Academy A. G. Werner, who died in 1817. In 1826 Mohs became full professor of mineralogy at the University of Vienna. At the same time he was assigned curator of the Imperial Mineralogical Collection, in which the van der Nüll collection of minerals was incorporated in 1827. In 1835 Mohs resigned. He became Bergrath which meant being an imperial counselor in charge of mining affairs, published under orders from his department an instruction on mining and was commissioned with the establishment of a montanistic museum in Vienna.
As part of this task, he started classifying minerals by their physical characteristics, instead of their chemical composition, as had been done traditionally. This emphasis on physical characteristics was at odds with the prevailing chemical systematics. However, both Theophrastus and Pliny the Elder had compared the relative hardness of minerals known to them in the ancient world, including diamond and quartz. They knew that diamond could scratch quartz, so showing it to be harder. This became the basis of the hardness scale developed by Mohs. The hardest mineral, diamond was given a value of 10 and softer minerals such as talc were given the very low value of 1 (unity). Other minerals were given intermediate values, depending on their ability to scratch another mineral in the scale. Thus gypsum was given the value 2 because it will scratch talc crystals, and calcite the value 3 because it will scratch gypsum. Minerals are also now classified by chemical characteristics, but the physical properties are still useful in field examination.