Djurleite

Crystal System: Monoclinic
Status of Occurrence: Confirmed Occurrence
Distribution: Locally Abundant
Chemical Composition: Copper sulphide
Chemical Formula: Cu31S16
Method(s) of Verification: Porth Ysgo - XRD (Natural History Museum, 4674F); Great Orme mines - reflected light microscopy (Ixer & Davies, 1996); Dolyhir Quarry & Penrhyn Slate Quarry - XRD (NMW X-1461 & X-1673 respectively).

Chemical Group:

  • Sulphides

Geological Context:

  • Supergene: in situ natural oxidation & weathering deposits
Massive, grey metallic djurleite from Dolyhir Quarry, Old Radnor, Powys. Specimen 25 mm across. National Museum of Wales specimen. Photo T.F. Cotterell, © National Museum of Wales.
Introduction: this species, along with chalcocite, digenite and a number of others, belongs to a group of minerals which are difficult to distinguish as they look superficially similar and each contains a subtly different copper/sulphur ratio. They are distinguishable in polished section with care and a lot of experience. Quantitative electron microprobe analysis has to be of the highest accuracy in order to obtain reliable identifications, and it is not unreasonable to recommend that any undifferentiated grey supergene copper sulphide be simply referred to as such until detailed analytical work confirms which actual species is/are present. Djurleite occurs in zones of supergene enrichment overlying ore deposits in which chalcopyrite, tetrahedrite and other primary copper ores are present.
Occurrence in Wales: there are four confidently identified djurleite occurrences from Wales, all of which are within supergene mineral assemblages. This number is likely to increase as more detailed work is carried out on grey supergene copper sulphides, occurences of which are widespread.

Key Localities:

  • Dolyhir Quarry, Old Radnor, Powys: grey, massive supergene copper sulphide forming pods within fractures in Dolyhir Limestone has been labelled by many mineral collectors as 'chalcocite'. Detailed analysis (XRD & EPMA) has shown that the main phase is actually djurleite (T.F. Cotterell, unpublished data).
  • Great Orme Copper Mines, Llandudno, Gwynedd: reported by Ixer & Davies (1996) on the basis of optical identification as 20 µm rims and 200 µm wide patches enclosing cuprite or relict chalcopyrite.
  • Penrhyn Quarry, Bethesda, Gwynedd: masses of dark grey metallic copper sulphide from this locality have been shown by XRD to be djurleite (T.F. Cotterell, unpublished data).
  • Porth Ysgo, Aberdaron, Llŷn, Gwynedd: noted on the basis of XRD record 4674F at the Natural History Museum, London.

References:

  1. Ixer, R.A. & Davies, J., 1996. Mineralisation at the Great Orme Copper Mines, Llandudno, North Wales. U.K. Journal of Mines and Minerals, 17, 7-14.