Hydrozincite

Crystal System: Monoclinic
Status of Occurrence: Confirmed Occurrence
Distribution: Locally Abundant
Chemical Composition: Zinc carbonate hydroxide
Chemical Formula: Zn5(CO3)2(OH)6
Method(s) of Verification: All by XRD: Castell Mine (NHM, 4672F); Cwmleyshon Quarry (NHM, 2979F); Dylife Mine (NHM, x13803 & 1600F); Esgair Hir Mine (NHM, 6789F); Machen Quarry (NMW X-840 & X-910); Parc Mine (NHM, 4881F); Van Mine (NHM, 1613F); Gwaithgoch Mine (NMW X-1527).

Geological Context:

  • Supergene: post-mining oxidation & weathering deposits
Introduction: hydrozincite is a common secondary carbonate mineral which forms typically as post-mining flowstone, on mine walls associated with zinc orebodies, particularly those containing sphalerite.
Occurrence in Wales: traces of hydrozincite are present at most localities where sphalerite has been subjected to weathering, particularly within mine dumps, but the more spectacular occurrences occur where hydrozincite has precipitated as flowstone within underground mine workings. Large masses of brilliant white flowstone have been collected over the years from both working and abandoned zinc mines across the Principality. G.J. Williams, the former H.M. Mine Inspector for North Wales, collected fine large specimens of hydrozincite from many of the working mines during the early 20th Century including Van, Parc and Aberllyn. Hydrozincite occurs in some degree or another at most of the mines in the Central Wales and Llanrwst Orefields. The richest specimens have been found in underground workings where, precipitation of hydrozincite is frequently ongoing. Modern discoveries of this nature have been made at Bwlch-glas, Gwaithgoch and Cwmystwyth mines in the Central Wales Orefield and also at Castell Carn Dochan Mine near Bala in Gwynedd. Somewhat surprisingly given the abundance of sphalerite in Flintshire, hydrozincite is only recorded in traces, usually dump-formed. It appears that conditions are preferentially suited to the development of the zinc carbonate smithsonite instead. In South Wales, traces of hydrozincite occur, occasionally coating sphalerite crystals within ironstone nodules in the South Wales Coalfield, but by far the richest samples are to be found in the dolomitic limestone quarries near Machen. At Machen Quarry, hydrozincite forms massive white powdery patches within the upper reaches of barite veins containing altered primary galena, sphalerite and chalcopyrite. Similar material is present at the nearby Cwmleyshon Quarry.

Key Localities:

  • Aberllyn Mine, Llanrwst Orefield, Gwynedd: described by Bevins & Mason (1998) as common on tips. The mineral collection of the National Museum of Wales contains specimens (NMW 27.111.GR.413, 414 & 415) collected in 1917 from underground workings. Both glossy white crusts and thin pale greenish white coatings of the nickeloan variety are present, on shale host rock. Of particular note was the discovery, on one of the specimens (NMW 27.111.GR.414), of the new mineral namuwite, forming a thin encrustation on hydrozincite (Bevins et al., 1982).
  • Bryntail Mine, Llanidloes, Powys: thin coatings of powdery hydrozincite occur on mudstone breccia from Murray’s Shaft dump (National Museum of Wales specimen no. NMW 98.35G.M.333).
  • Bwlch-glas Mine, Tal-y-bont, Ceredigion: hydrozincite flowstone is noted by Bevins & Mason (1997). Specimens in the mineral collection of the National Museum of Wales (collected by John Mason c. 1985) show thick (3 mm) glossy white crusts coating mudstone and cementing fragments of unconsolidated rock from the floor of the East Drift. A further habit is rippled crusts consisting of sparkling lath-like microcrystals.
  • Castell Carn Dochan Mine, Llanuwchllyn, Bala, Gwynedd: post-mining hydrozincite occurs underground (Bevins & Mason, 1998) in No. 3 adit, as evidenced by specimens in the mineral collection of the National Museum of Wales. Both friable porous creamy-white stalactitic growths (NMW 92.15G.M.4) and extensive (to areas 15 x 23 cm) glossy crusts on veinstone occur.
  • Castell Mine, Ponterwyd, Ceredigion: hydrozincite is recorded by Jones & Moreton (1977). On the main dumps hydrozincite occurs commonly as white coatings on weathered sphalerite and ferroan dolomite veinstone.
  • Cwmleyshon Quarry, Draethen, South Wales: hydrozincite is abundant (Bevins & Mason, 2000).
  • Cwmystwyth Mine, Cwmystwyth, Ceredigion: a sample collected by J. Jones in 1980 (NMW 87.73G.M.224) from stopes above Level Fawr, consists of a small fragment of rock (6 x 4 x 3 cm) completely coated by a thin crust of hydrozincite.
  • Esgair Fraith Mine, Tal-y-bont, Ceredigion: very thin coatings of pale green to white hydrozincite on weathered calcite are in the National Museum of Wales Mineral Collection (NMW 90.14G.M.354).
  • Gwaithgoch Mine, Pontrhydygroes, Ceredigion: attractive hydrozincite flowstone occurs underground (T.F. Cotterell, unpublished data).
  • Llanfyrnach Mine, Pembrokeshire: abundant dump formed hydrozincite is noted by Bevins & Mason (1997). A specimen in the mineral collection of the National Museum of Wales (NMW 78.33G.M.125) collected in 1974, displays poorly formed powdery coatings.
  • Llanrwst Mine, Llanrwst, Gwynedd: extensive thin glossy coatings completely enclose iron-stained rock fragments. A specimen in the R.J. King Collection (now NMW 83.41G.M.5557) was collected in 1952.
  • Machen Quarry, Caerphilly, South Wales: powdery white hydrozincite occurs associated with hemimorphite and aurichalcite within barite veinstone exposed in the upper benches of the quarry (Plant & Jones, 1995). Hydrozincite is common within this assemblage.
  • Nant-y-creiau Mine, Devil’s Bridge, Ceredigion: Bevins & Mason, 1997 note abundant coatings of hydrozincite. At Nantycreiau, hydrozincite forms extensive thin white powdery coatings, particularly on weathered calcite veinstone which produces an attractive contrast of colours under UV light, as displayed by National Museum of Wales specimen no. NMW 98.35G.M.540.
  • Parc Mine, Llanwrst, Gwynedd: Alwan & Williams (1979) described nickeloan hydrozincite, a new variety of hydrozincite from the Parc Mine. Superb rippled hydrozincite flowstone was collected from old workings above No. 3 Level by R.W. Barstow in 1978. A particularly fine specimen formerly in R.W. Barstow’s private collection, is now in the mineral collection of the National Museum of Wales (NMW 85.70G.M.29) and shows hydrozincite richly encrusting calcite-sphalerite veinstone.
  • Penyclun Mine, Llanidloes, Powys: common dump-formed coatings listed by Bevins & Mason (1997).
  • Trecastell Mine, Henryd, Gwynedd: hydrozincite is present in the adit level as glossy white flowstone precipitated on unconsolidated shale fragments, probably derived from the tunnel floor (National Museum of Wales Mineral Collection no. NMW 83.41G.M.5560, ex R.J. King Collection).
  • Van Mine, Llanidloes, Powys: spectacular samples of rippled flowstone forming thick coatings underground were collected during working operations at the mine. The finest specimens from Van are without a doubt the richest to have been discovered in Wales. The G.J. Williams Mineral Collection in the National Museum of Wales contains two fine pieces. NMW 27.111.GR.14 is an exceptional specimen consisting of a plank of wood almost completely covered by thick rippled hydrozincite flowstone measuring 33 x 17 x 6 cm. Hydrozincite flowstone from Van, can, reach 6 cm thick (NMW 83.41G.M.5558, ex R.J. King Collection), typically being very porous and consequently very light to the touch.

References:

  1. Alwan, A.K. & Williams, P.A., 1979. Nickeloan hydrozincite: a new variety. Mineralogical Magazine, 43, 397-398.
  2. 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.
  3. 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.
  4. 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.
  5. Bevins, R.E., O’Brien, P., Turgoose, S., & Williams, P.A., 1982. A New find of nickeloan hyrozincite in the Parc Mine, North Wales. Journal of the Russell Society, 1, 19-21.
  6. Bevins, R.E., Turgoose, S., & Williams, P.A., 1982a. Namuwite, (Zn,Cu)4SO4(OH)6.4H2O, a new mineral from Wales. Mineralogical Magazine, 46, 51-54.
  7. Jones, J.A. & Moreton, N.J.M., 1977. The Mines and Minerals of Mid-Wales 40pp.
  8. Plant, S.P. & Jones, I.E., 1995. Minerals of Machen Quarry, Mid Glamorgan, Wales. Journal of the Russell Society, 6(1), 31-36.