Carl Wilhelm Casimir Fuchs (1837-1886) was a German geologist, mineralogist, and botanist. From 1876, he served as an associate professor of geology at the University of Heidelberg. The field examination of rocks using a magnifying glass and hydrochloric acid is still the first step in many mineralogical investigations today. The precise description of the structure, texture, and mineral composition is of primary importance. Some methods of spectroscopy, such as Mössbauer spectroscopy in tin mining, are already being applied in the field. In the laboratory, samples are prepared: thin sections or polished sections are made for polarizing microscopy in transmitted or reflected light. Rocks are examined in transmitted light and ores in reflected light. Illustrated with 25 black-and-white images and identification tables. Reprint of the original edition from 1890.