Mohs \ˈmōs\ Friedrich (1773–1839), German mineralogist. Mohs's chief scientific contribution was establishing systematic mineralogy on a new basis. He was placed in charge of several important mineral collections, of which he later published systematic descriptions. In the early 1820s he developed a new method of mineral classification that focused on the arrangements of minerals in crystal systems based on external symmetry. In 1812 he introduced the Mohs' scale of hardness for minerals. By the 1820s the scale had been widely adopted by other mineralogists.