The well known “Saalfelder Feengrotten” originated from an old aluminium mine called “Jeremiasglück”. The mine has been working from 1943 to 1945; the oldest formations have an age of about 350 years. Such formations were formed by an oxidation process which explains the rather fast growth rate in comparison to the growth rate of calcite formations. In the “Feengrotten” rare minerals can be found: the most common is a soft unstable compound, the diadochite (iron(III) phosphate). The control of the lampenflora is rather complicate and it is obtained with some compounds normally used in caves. The “Feengrotten” are visited yearly by about 250,000 persons and the global number of visitors up to now is more than 15 millions of persons.
Die Saalfelder Feengrotten: ein Schaubergwerk mit Höhlencharkter.
International Journal of Speleology,
Available at: https://scholarcommons.usf.edu/ijs/vol23/iss1/13