Carbonate-cyanotrichite

Crystal System: Orthorhombic
Status of Occurrence: Confirmed Occurrence
Distribution: Rare
Chemical Composition: Copper aluminium carbonate sulphate hydroxide hydrate
Chemical Formula: Cu4Al2(CO3,SO4)(OH)12.2H2O
Method(s) of Verification: Wedding Cave Mine - XRD at Manchester Museum (X-ray reference number MANCH:XRD163).

Geological Context:

  • Supergene: post-mining oxidation & weathering deposits
Sky-blue crust of carbonate-cyanotrichite from Wedding Cave Mine. Specimen National Museum of Wales (NMW 2003.13G.M.1). Photo D.I. Green, © National Museum of Wales.
Bright blue finely crystallized crust of carbonate-cyanotrichite. Wedding Cave Mine, Bwlch-gwyn, Wrexham. National Museum of Wales Collection. Photo T.F. Cotterell, © National Museum of Wales.
Introduction: a secondary mineral that typically forms in post-mining environments, particularly in underground mine workings where copper-bearing ore bodies are exposed. In Wales carbonate-cyanotrichite has been observed in association with secondary lead minerals, including, anglesite, cerussite and linarite.
Occurrence in Wales: records of carbonate-cyanotrichite from the British Isles are limited, but where it does occur, attractive crusts of a rich sky-blue colour coat mine walls. To date only one locality has been verified from Wales (Green, 1995), but material of similar appearance has been observed at a mine in the Dolgellau Gold-belt and awaits further research.

Key Localities:

  • Wedding Cave Mine, Bwlchgwyn, Wrexham: carbonate-cyanotrichite occurs in the underground workings at this small mine and forms sky-blue crusts covering sizeable (to 5 cm2) areas of sandstone wall-rock. These crusts consist of interlocking spheroidal aggregates of minute feathery crystals.

References:

  1. Green, D.I., 1995. Carbonate-cyanotrichite from the Wedding Cave mine, Bwlchgwyn, Clwyd. UK Journal of Mines & Minerals, 15, 19.