Crystal System: Monoclinic
Status of Occurrence: Confirmed Occurrence
Distribution: Rare
Chemical Composition: Copper arsenate hydroxide
Chemical Formula: Cu3(AsO4)(OH)3
Method(s) of Verification: Great Orme - EMPA (Jenkins & Johnson, 1993).

Chemical Group:

  • Arsenates

Geological Context:

  • Supergene: in situ natural oxidation & weathering deposits
Introduction: clinoclase is a supergene mineral found typically with other copper-bearing arsenates (e.g. olivenite) in the oxidized zones of primary ore deposits carrying copper ores (e.g. chalcopyrite) in association with arsenic minerals (e.g. arsenopyrite).
Occurrence in Wales: supposed specimens of clinoclase (according to the labels) in the National Museum of Wales Collection have failed to yield anything more than a very diffuse X-ray diffraction pattern. The specimens, from Tan-y-garth Mine in the Ogwen Valley, Gwynedd, consist of bright blue friable coatings on slate. Similar, essentially amorphous friable 'copper-stains' are in fact known from many Welsh localities, and tend to represent dried out sulphate gels. More recently, however, clinoclase has been confirmed from the Great Orme, Llandudno (see key locality entry).

Key Localities:

  • Great Orme Copper Mines, Llandudno, Gwynedd: clinoclase is mentioned, along with erythrite, as occurring in traces at this locality but no detailed description is provided (Jenkins & Johnson, 1993).


  1. Jenkins, D.A. & Johnson, D.B., 1993. Abandoned metal mines: a unique mineralogical and microbiological resource. Journal of the Russell Society, 5, 40-44.