Mineral Database (Saesneg yn unig)

Mineral Database (Saesneg yn unig)
Mineralogy of Wales

Azurite

Crystal System: Monoclinic
Formula: Cu3(CO3)2(OH)2
Status of Occurrence: Confirmed Occurrence
Distribution: Locally Abundant
Chemical Composition: Copper carbonate hydroxide
Method(s) of Verification: Most localities - visual identification by experienced mineralogists. Bwlchrhennaid Mine - XRD at the National Museum of Wales (NMW X-1028); Pant Quarry - XRD (NMW X-1196).
Chemical Group:
  • Carbonates
Geological Context:
  • Supergene : in situ natural oxidation & weathering deposits
Introduction: azurite typically forms in the oxidized zones of copper-bearing hydrothermal mineral deposits. It is preferentially formed in neutral to slightly alkaline pH conditions. The commoner copper carbonate, malachite, is more abundant because it is stable over a wider pH range. Many significant azurite localities are characterized by significant carbonate gangue or by a carbonate (limestone) host-rock. Associated minerals include malachite, cuprite and various copper arsenates and phosphates. Care must be taken not to mistake azurite for the similar-looking (to the inexperienced eye) basic copper-lead sulphate linarite. However, the crystal morphology and associated minerals usually aids diagnostic identification: linarite forms in much more acidic conditions in sulphate-dominated assemblages. Being a carbonate, azurite also dissolves with effervescence in acids.
Occurrence in Wales: there are several important localities for azurite in Wales: some well-known for many decades and others of more recent discovery. They are mainly confined to weathered ore deposits in carbonate-rich host-rocks, and it should be noted that some early reports of azurite from Central Wales are suspect in this context, as they remain unconfirmed and the localities are rich in linarite. Old specimens of azurite in collection of the National Museum of Wales show that it was known from the Great Orme at Llandudno and from old copper mines at Llanymynech near Oswestry many years ago: however much finer examples of the mineral have emerged in recent years, with the most important locality in terms of specimens being Dolyhir Quarry near Kington in the Borders area. Here, over the past decade, intermittent exposures in which well-crystallized azurite occurred in abundance have, fortunately, been accessed by collectors prior to being quarried away.
Key Localities:
  • Central Wales Orefield: although azurite was reported from a number of localities by Jones & Moreton (1977), detailed field and laboratory work by a number of experienced mineralogists since has failed to confirm these reports, although linarite was found at each site. Azurite has only been positively identified at three Central Wales mines to date. At Bwlchrhennaid Mine a small number of specimens were found in 1985, showing glittering crusts of microcrystals associated with malachite (Rothwell & Mason, 1992). At Lletty Evan-hen Mine azurite forms crystalline masses to 2 mm in small quartz cavities, while at South Nantycar Mine rare crystalline masses to 6 mm have been collected (both of the latter localities represented by specimens in the S.A. Rust Collection).
  • Dolgellau Gold-belt, Gwynedd: azurite is uncommon in this part of Wales, but has been recorded as rare encrustations and microcrystals associated with chalcopyrite and malachite from the Friog trials and a roadside vein exposure, both in Coed-y-Brenin (Bevins & Mason, 1998). Traces of azurite also occur as part of the supergene assemblage in exposures of the Coed-y-Brenin porphyry-copper deposit in the same area.
  • Great Orme Copper Mines, Llandudno, Gwynedd: azurite is not particularly common here but some fine specimens showing crystals on a crystalline dolomite matrix are known. In addition, small spheroidal nodules of azurite occur within a thin (0.3 m) shale horizon (Ixer & Davies, 1996).
  • Llanymynech copper mines, Powys: finely crystallized azurite on old specimens (e.g. NMW Collection, NMW 83.41G.M4786).
  • Pant Quarry, Halkyn Mountain, Clwyd: excellent azurite crystals were found here in 1998 (Bevins & Mason, 1999). Crystals, exceptionally to 7 mm, occurred on calcite containing abundant oxidized chalcopyrite inclusions and pseudomorphs of azurite after chalcopyrite were also noted. Some specimens included purple fluorite and/or hydrocarbon within the primary assemblage. Malachite was commonly present. The locality has since largely disappeared under a haulage road.
  • Pant-y-Gaseg Mine, Anglesey: azurite is known on specimens, with malachite, from Pant-y-Gaseg Mine, while specimen NMW 60.250.GR2 in the National Museum of Wales Collection is labellled as being from Parys Mountain. However, the highly acidic environment of the oxidized zone at Parys Mountain is incompatible with azurite formation and stability and the specimen is suspected to be misprovenanced.
  • South Wales: azurite is uncommon in South Wales, but has been found at Hendy Quarry, near Llantrisant (British Micromount Society Newsletter no. 35) and in the Locks Common Borehole near Porthcawl (Fletcher & Young, 1988). An interesting record of azurite and malachite occurring in Devonian sandstones along the South Pembrokeshire coast (Dixon, 1921) deserves investigation.
References:
  • Bevins, R.E. & Mason, J.S., 1998 Welsh Metallophyte and metallogenic evaluation project: Results of a Minesite Survey of Gwynedd.  National Museums of Wales, Cardiff.
  • Bevins, R.E. & Mason, J.S., 1997 Welsh metallophyte and metallogenic evaluation project: Results of a minesite survey of Dyfed and Powys.  CCW Contract Science Report No. 156. National Museums & Galleries of Wales.
  • Bevins, R.E. & Mason, J.S., 1999 Welsh Metallophyte and metallogenic evaluation project: Results of a Minesite Survey of Clwyd.  National Museums & Galleries of Wales, Cardiff.
  • Dixon, E.E.L., 1921 The Geology of the South Wales Coalfield. Part XIII. The Country around Pembroke and Tenby.  Memoirs of the Geological Survey of England and Wales. Explanation of Sheets 244 and 245.
  • Fletcher, C.J.N. & Young, B.R., 1988 Rosasite from Bute Quarry, Mid Glamorgan. The first reported occurrence in Wales.  Journal of the Russell Society, 2(1), 19-23.
  • 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.
  • Jones, J.A. & Moreton, N.J.M., 1977 The Mines and Minerals of Mid-Wales  40pp.
  • Rothwell, M. & Mason, J.S., 1992 Wulfenite in the British Isles.  UK Journal of Mines & Minerals, 11, 30-41.