Karl August Lossen (born Kreuznach (Rhineland), 5 January 1841; died Berlin, 24 February 1893) was a German petrologist and geologist. After finishing his studies at the gymnasium of Kreuznach in 1859 Lossen became a mining engineer; he began by two and a half years of practical work, then studied at the Universities of Berlin and Halle, where he graduated in 1866; in the same year he became assistant geologist of the Prussian national geological survey. He began immediately his well-known petrolographic studies of the Harz Mountains, which lasted till his death. In 1870 he became instructor in petrology at the Berlin mining academy, and at the same time lecturer at the university. In 1873, he was made a member of the newly founded Prussian National Geological Institute, and in 1882 receiv