Alum shale

Alum or Vitriolschiefer is with pyrite ( iron sulphide ( FeS2 ) ) and coal interspersed shale. Because of its coloring alum is also classified in the black shales.

The rock is in the weathering free alum, a salt mixture of potassium and aluminum sulfate, which was once widely used among others in tanneries. The alum was first smelted in Alaunwerken from alunite, after 1500 the production of alum has been developed. After 1800, dissolved chemical extraction methods alunite and alum shale from the source of alums.

In some shales formed during the weathering of sulfates of copper or zinc, the so-called vitriols.