Crystal System: Triclinic
Status of Occurrence: Confirmed Occurrence
Distribution: Locally Abundant
Chemical Composition: Copper sulphate hydrate
Chemical Formula: CuSO4.5H2O
Method(s) of Verification: Parys Mountain - XRD (Dr. D. Jenkins, University College of North Wales, Bangor).

Geological Context:

  • Supergene: post-mining oxidation & weathering deposits
Well crystallized specimen of chalcanthite from 16 fathom level, Carreg-y-Doll Lode, Parys Mountain. Specimen National Museum of Wales (NMW 83.41G.M.8475) ex R.J. King Collection. Photo D.I. Green, © National Museum of Wales.
Introduction: chalcanthite is a secondary mineral which develops in the oxide zone of copper-bearing ore bodies, particularly in arid regions. Natural crystals are very rare, although crystals are easily made artificially
Occurrence in Wales: the first written account of chalcanthite from Wales appears to be that by Aikin (1797), reporting the presence of ‘sulphate of copper, crystallized and in solution’ from Parys Mountain, on Anglesey. In 1858, Greg & Lettsom describe how at Pary’s mine, strips of iron are laid in the slime containing chalcanthite in solution and, when the iron is dissolved, copper is deposited in its place; for every ton of iron consumed there is thrown down a deposit of an equal weight of copper mud, containing about 12 per cent of copper. Clearly a considerable amount of copper was present within the mine waters, which, being highly acidic results in the deposition of chalcanthite on mine walls. A number of very rich, crystallized specimens reported as being from underground workings at Parys Mountain are held by the National Museum of Wales. Doubt remains over the authenticity of a number of these pieces as one particular specimen is perfect in terms of colour and form and looks to have been laboratory grown. Others however, show accurate provenancing and contain loose fragments of mine material within their growth structure.

Key Localities:

  • Parys Mountain, Anglesey: the former Mines Inspector for North Wales, G.J. Williams had, in his collection a number of crystallized specimens from Mona Mine. These pieces now reside in the National Museum of Wales Collection, along with well crystallized examples collected from the 16 fm. level on Carreg-y-Doll Lode in Parys Mountain during the 1950s (see for example NMW specimen no. 83.41G.M.8475). Stalactites composed of chalcanthite have also been collected from Carreg-y-Doll Lode.


  1. Aikin, A., 1797. Journal of a tour through North Wales and part of Shropshire, with observations in mineralogy and other branches of natural history. London, 231pp
  2. Greenly, E., 1919. The Geology of Anglesey. Memoirs of the Geological Survey of Great Britain, 980pp (2 volumes).
  3. Greg, R.P. & Lettsom, W.G., 1858. Manual of the Mineralogy of Great Britain and Ireland. John van Voorst, London, 483pp.