Copiapite

Crystal System: Triclinic
Status of Occurrence: Confirmed Occurrence
Distribution: Rare
Chemical Composition: Iron sulphate hydroxide hydrate
Chemical Formula: Fe2+Fe3+4(SO4)6(OH)2.20H2O
Method(s) of Verification: Parys Mountain - XRD (Dr. D. Jenkins, University College of North Wales, Bangor); Old Taff's Well iron ore mine - XRD at the National Museum of Wales (XRD no. NMW X-1775).

Chemical Group:

  • Sulphates

Geological Context:

  • Supergene: post-mining oxidation & weathering deposits
  • Supergene: in situ natural oxidation & weathering deposits
Introduction: copiapite forms in highly acidic conditions, particularly in the altered portions of pyrite-rich sulphide ore bodies and in post-mining environments, where it is typically associated with gypsum and a wide range of iron-bearing sulphate minerals.
Occurrence in Wales: copiapite is known from two localities in North Wales, where it has formed in underground mine workings as a product of the post-mining oxidation of pyrite. A further occurrence, in South Wales, was confirmed on a specimen collected from the dumps of an old iron mine. Given the number of localities where similar environments exist throughout 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: copiapite occurs rarely at this locality with copious mounds of fibroferrite and jarosite on the floor of the mine (Johnson et al., 1979).
  • Parys Mountain, Anglesey: present as one of a range of ferric sulphates found in overhangs, recesses and other sites protected from the elements, copiapite is present in the two major opencasts (Jenkins et al., 2000).
  • Taff's Well, Mid Glamorgan: yellow efflorescence present on National Museum of Wales specimen NMW 85.14G.M.64 labelled as sulphur from Old Taff's Well iron ore mine has been identified as copiapite with ammoniojarosite and minor gypsum (T.F. Cotterell, unpublished data).

References:

  1. 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.
  2. Johnson, D.B., Kelso, W.I., & Jenkins, D.A., 1979. Bacterial streamer growth in a disused pyrite mine. Environmental Pollution, 18, 107-118.