German petrographer, born at Bonn in 1838. He was educated at Bonn, where he trained as a mining engineer, but a journey he made to Iceland and the Faeroe Is., Scotland and England, and a meeting with Henry Clifton Sorby attracted him to the study of microscopical petrography, then a comparatively new science. He became professor of mineralogy and geology successively at Lemberg (1863), Kiel (1868) and Leipzig (1870), retiring from the last-named post in 1909. He did much to develop the study of petrography, and his Lehrbuch der Petrographie (1866; 2nd ed., 1893–4) is a standard work on the subject. He was an hon. D.Sc. of Oxford, and also a foreign member of the Royal Society and an honorary member of the Mineralogical Society. He died at Bonn on the 11th of June 1912.
His numerous papers and essays include Geologische Skizze von der Westküste Schottlands (1871); Die Struktur der Variolite (1875); Microscopical Petrography (in Report of U.S. Geol. Exploration of 40th Par., vol. vi., 1876); Limurit aus der Vallée de Lesponne (1879); Über den Zirkon (1880). His separate works include Lehrbuch der Petrographie (1866; 2nd ed., 1893, 1894); Die mikroskopische Beschaffenheit der Mineralien und Gesteine (1873).
