Grotta dello Zolfo, Italy
Speleothems: small masses
Frequency: Rare
Other geologic settings: Forms by reaction of sulfates from decomposing sulfides with aluminous minerals in shales and slates; in gossan or altered wall rock of pyritic deposits in arid regions; in coal seams; in relatively low-temperature fumaroles.
Other occurrence: crusts on floor and walls (Ruatapu Cave, New Zealand)
First description of cave occurrence: Bellini, R. 1901. La Grotta dello Zolfo nei Campi Flegrei. Bollettino della Società Geologica Italiana 20(3): 470-475
First description of non-cave occurrence: Beudant, F.S. 1832. Alunogène, sulfate d’alumine. Traité Élémentaire de Minéralogie, 2nd Edition Paris: 488-492
Other cave locations & References: Ruatapu Cave, New Zealand - Cody, A.D. 1978. Ruatapu Cave. New Zealand Speleological Bulletin 6(108): 184-187 Serpent Cave, France: Audra, P. & Hobléa, F. 2007. The first cave occurence of jurbanite [Al(OH SO4)·5H2O, associated with alunogen [Al2(SO4)3·17H2O] and tschermigite [NH4Al(SO4)2·12H2O]: thermal-sulfidic Serpents Cave, France. Journal of Cave and Karst Studies 69: 243–249
volcanic tuff
Group: Sulfates
Chemical formula: Al2(SO4)3(H2O)12·5H2O
[According to the official IMA-CNMNC List of Mineral Names (http://nrmima.nrm.se/imalist.htm)]
Varieties: keramoalunite (unnofficial variety) - reported from a cave inside the crater of Volcano Island, Italy (now completely destroyed) in 1792, and from Alun Cave, Volcano Island (1914) (where it is no longer present).
Deposition and stability: It resulted from the reaction of fumarole gasses upwelling in the salt lake of the cave, with the tuff of the cave walls.
Color: white to transparent
covered by tufts of acicular crystals of pickeringite (Grotta dello Zolfo, Italy)
associated with other white evaporitic minerals: gypsum, potassium alum, anhydrite (Ruatapu Cave, New Zealand)
associated with other sulfate minerals: jurbanite and tschermigite (Serpents Cave, France)
- Triclinic