As part of this task, he started classifying minerals by their physical characteristics, in spite 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. Minerals are now classified by chemical characteristics, but the physical properties are still useful in field examination.
In 1812, Mohs became a professor in Graz, and moved six years later to Freiberg, Saxony, before finally settling down to practice his profession in Vienna in 1826. Mohs died during a trip to Agordo, Italy in 1839, at the age of 66.
Wilhelm von Gümbel: Mohs, Friedrich. In: Allgemeine Deutsche Biographie (ADB). Band 22, Duncker & Humblot, Leipzig 1885, S. 76–79.
Josef Zemann: Mohs Friedrich, Montanist, Mineraloge und Kristallograph. In: Österreichisches Biographisches Lexikon 1815–1950 (ÖBL). Band 6, Verlag der Österreichischen Akademie der Wissenschaften, Wien 1975, ISBN 3-7001-0128-7, S. 345.
Johannes Uray, Chemische Theorie und mineralogische Klassifikationssysteme von der chemischen Revolution bis zur Mitte des 19. Jahrhunderts. In: Berhard Hubmann, Elmar Schübl, Johannes Seidl (Hgg.), Die Anfänge geologischer Forschung in Österreich. Beiträge zur Tagung „10 Jahre Arbeitsgruppe Geschichte der Erdwissenschaften Österreichs“ von 24. bis 26. April 2009 in Graz. Graz 2010, S 107-125.