Alum slate
Former alum slate mine in the Saalfeld fairy grottoes
Alum slate or vitriol slate is a clay slate interspersed with pyrite (iron sulfur (FeS 2 )) and coal . Because of its color, alum slate is also classified as black slate .
When weathered, the rock releases alum , a mixture of salts made from potassium and aluminum sulphate that was previously used extensively in tanneries , among other things . The alum was initially extracted from alunite in alum factories , after 1500 the extraction from alum slate was developed. After 1800 chemical extraction methods replaced alunite and alum slate as a source for alums .
In some shales formed during the weathering and sulphates of copper or zinc , called vitriols .
Individual evidence
- ^ Hans Murawski, Wilhelm Meyer: Geological dictionary . 11th edition. Elsevier / Spektrum, Heidelberg 2004, ISBN 3-8274-1445-8 , pp. 262 .