CLAUSTHAL, or Klausthal, a town of Germany, in the Prussian Harz, lying on a bleak plateau, 1860 ft. above sea-level, 50. m. by rail W.S.W. of Halberstadt. Pop. (1905) 8565. Clausthal is the chief mining town of the Upper Harz Mountains, and practically forms one town with Zellerfeld, which is separated from it by a small stream, the Zellbach. The streets are broad, opportunity for improvement having been given by fires in 1844 and 1854; the houses are mostly of wood. There are an Evangelical and a Roman Catholic church, and a gymnasium. Clausthal has a famous mining college with a mineralogical museum, and a disused mint. Its chief mines are silver and lead, but it also smelts copper and a little gold. Four or five sanatoria are in the neighbourhood. The museum of the Upper Harz is at Zellerfeld.
Clausthal was founded about the middle of the 12th century in consequence probably of the erection of a Benedictine monastery (closed in 1431), remains of which still exist in Zellerfeld. At the beginning of the 16th century the dukes of Brunswick made a new settlement here, and under their directions the mining, which had been begun by the monks, was carried on more energetically. The first church was built at Clausthal in 1570. In 1864 the control of the mines passed into the hands of the state.