Mineral Database

Mineral Database
Mineralogy of Wales

Chalcoalumite

Crystal System: Monoclinic
Formula: CuAl4(SO4)(OH)12.3H2O
Status of Occurrence: Confirmed Occurrence
Distribution: Rare
Chemical Composition: Copper aluminium sulphate hydroxide hydrate
Method(s) of Verification: Bontddu - XRD (Natural History Museum, X-ray no. 6256F).

Pale blue-green chalcoalumite crust from Britannia Mine, Snowdon, Gwynedd. Specimen 8 cm in length. National Museum of Wales Collection (NMW 83.18G.M.44). Photo T.F. Cotterell, © National Museum of Wales.

Chemical Group:
  • Sulphates
Geological Context:
  • Supergene : in situ natural oxidation & weathering deposits
Introduction: chalcoalumite is a rare secondary mineral typically developed in the oxidized zone of copper-bearing deposits.
Occurrence in Wales: records of chalcoalumite from Wales are few. Bevins et al. (1985) recorded rare chalcoalumite, associated with lanthanite-(Ce) from Sneyd's Level at Britannia Mine on Snowdon, whereas Saich & Rust (1987) describe extremely rare chalcoalumite from a small trial level near Bontddu in the Dolgellau Gold-belt. Further localities listed, without description, by Camm (1993) are regarded as dubious until additional information is available.
Key Localities:
  • Bontddu, Dolgellau, Gwynedd: chalcoalumite occurs extremely rarely, replacing laths of devilline on joints in veinstone and as a white replacement of both a tyrolite-like mineral and malachite in a trial level near Bontddu (Saich & Rust, 1987).
  • Britannia Mine, Snowdonia, Gwynedd: associated, although only rarely, with lanthanite-(Ce) in oxidized copper ore in Sneyd's Level (Bevins et al., 1985).
  • Frongoch Mine, Devil's Bridge, Ceredigion: listed without description by Camm (1993).
  • Goldsland Wood, Cwmavon, South Wales: listed without description by Camm (1993).
  • Great Orme Copper Mines, Llandudno, Gwynedd: listed without description by Camm (1993).
  • Llettyhen Mine, Bontgoch, Ceredigion: listed without description by Camm (1993).
References:
  • Bevins, R.E., Rowbotham, G., Stevens, F.S., Turgoose, S., & Williams, P.A., 1985 Lanthanite-(Ce), (Ce,La,Nd)2(CO3)3.8H2O, a new mineral from Wales, U.K.  American Mineralogist, 70, 411-413.
  • Camm, G.S., 1993 The Minerals and Mines of the Principality of Wales.  The Natural History Museum, London. 231pp.
  • Saich, D.A. & Rust, S.A., 1987 Micro-minerals from a trial level in Wales.  U.K. Journal of Mines and Minerals, No. 3, 3-4.