Mineral Database

Mineral Database
Mineralogy of Wales

Fibroferrite

Crystal System: Monoclinic
Formula: Fe3+(SO4)(OH).5H2O
Status of Occurrence: Confirmed Occurrence - 1st UK recording
Distribution: Rare
Chemical Composition: Iron sulphate hydroxide hydrate
Method(s) of Verification: Cae Coch Mine - XRD & wet chemical analysis; Parys Mountain - XRD.

Scanning electron micrograph of matted hair-like fibroferrite on gypsum from Cae Coch Mine. National Museum of Wales specimen (NMW 2002.9G.M.4). © National Museum of Wales.

Chemical Group:
  • Sulphates
Geological Context:
  • Supergene : post-mining oxidation & weathering deposits
Introduction: fibroferrite forms in highly acidic conditions, particularly in the altered portions of sulphide ore bodies and on the walls of underground mine workings in the post-mining supergene environment.
Occurrence in Wales: fibroferrite is known from two localities in North Wales, where it has formed in underground workings as a product of the post-mining oxidation of pyrite (Johnson & Jenkins, 1979; Jenkins et al., 2000). Given the number of localities where similar environments exist throughout North and Central Wales, but where the post-mining mineralogy remains to be investigated, it is anticipated that further occurrences may well come to light.
Key Localities:
  • Cae Coch Mine, Trefriw, Gwynedd: fibroferrite forms copious mounds with jarosite and, more rarely, copiapite on the floor of the mine (Johnson et al., 1979).
  • Parys Mountain, Anglesey: fibroferrite is present in minor amounts, with other iron sulphates, in overhangs and recesses and other sites protected from the elements within the two major opencasts (Jenkins et al., 2000).
References:
  • Jenkins, D. A., Johnson, D. B. & Freeman, C., 2000 Mynydd Parys Cu-Pb-Zn mines: mineralogy, microbiology and acid mine drainage.  pp. 161-179. In: Environmental Mineralogy: Microbial Interactions, Anthropogenic Influences, Contaminated Land and Waste Management (Cotter-Howells, J. D., Campbell, L. S., Valasami-Jones, E. & Batchelder, M., eds.). The Mineralogical Society of Great Britain & Ireland, London.
  • Johnson, D.B., Kelso, W.I., & Jenkins, D.A., 1979 Bacterial streamer growth in a disused pyrite mine.  Environmental Pollution, 18, 107-118.