Crystal System: Hexagonal
Status of Occurrence: Confirmed Occurrence - Type Locality In Wales
Chemical Composition: Zinc copper sulphate hydroxide hydrate
Chemical Formula: (Zn,Cu)4SO4(OH)6.4H2O
Method(s) of Verification: Aberllyn Mine - type specimen, characterized by XRD & chemical analyses (AAS & TGA);
Dylife Mine - XRD (NHM, 7529F); Frongoch Mine - XRD (NHM, see Green et al., 1996); Llywernog Mine - XRD (Wirth, 1993).
- Supergene: post-mining oxidation & weathering deposits
Pale blue namuwite crust (5 x 1.5 cm in extent) on the type specimen from Aberllyn Mine, Llanrwst, Gwynedd. National Museum of Wales Collection (NMW 27.111.GR.414), ex G.J. Williams Collection. © National Museum of Wales.
Turquoise-blue, platy, namuwite microcrystals from Frongoch Mine in the Central Wales Orefield. Specimen and photo S.A. Rust. © S.A. Rust.
Introduction: namuwite is a very rare secondary mineral species named in honour of the National Museum of Wales, the institution where the mineral was first discovered. Namuwite is a post-mining phase, typically formed through the oxidation of sphalerite-bearing veinstone in mine workings and within zinc- and copper-rich mine dumps.
Occurrence in Wales: the type specimen of namuwite from the Aberllyn Mine in the Llanrwst Orefield in Gwynedd, North Wales was acquired by the National Museum of Wales in the 1920s. Not until the late 1970s, did researchers, looking for nickeloan hydrozincite realise that a new species was present. Only this one specimen is known to exist from this mine.
During the 1980s and 90s mineral collectors interested in the unusual secondary minerals which, form attractive microcrystals in weathered veinstone on mine dumps from the Central Wales Orefield discovered namuwite at three more sites (Wirth, 1993; Bevins, 1994; Green et al., 1996). All of these recent finds show namuwite as small aggregates intimately associated with other post-mining secondary species, but rarely display crystals to 0.5 mm – large for the species.
Namuwite remains a very rare mineral in Wales and requires experience to identify it from similar blue-green secondary species.
- Aberllyn Mine, Llanrwst Orefield, Gwynedd: only one specimen (NMW 27.111.GR.414) is known from this, the type locality. On this, namuwite is present as minute (< 60 μm across) hexagonal plates aggregated into an area 1.5 x 5.0 cm and up to 0.5 cm thick on hydrozincite coating sphalerite-bearing breccia (Bevins et al., 1982).
- Dylife Mine, Penegoes, Powys: namuwite occurs, associated with schulenbergite on altered sphalerite, forming translucent, platy, blue-green hexagonal crystals (Bevins, 1994).
- Frongoch Mine, Devil's Bridge, Ceredigion: very rare, milky, pale blue to pale blue-green pseudohexagonal platy crystals to 0.5 mm and rosetted crystal clusters on quartz-galena veinstone (Wirth, 1993; Green et al., 1996). At Frongoch, namuwite is clearly post-mining in origin and late in the paragenesis, typically overgrowing langite, wroewolfeite, susannite or hydrocerussite (Green et al., 1996).
- Llywernog Mine, Ponterwyd, Ceredigion: namuwite has been collected from the mine dumps by S. Rust (British Micromount Society Newsletter no. 35).
- Bevins, R.E., 1994. A Mineralogy of Wales National Museum of Wales, Geological Series No. 16, Cardiff, 146pp.
- 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.
- Green, D.I., Rust, S.A. & Mason, J.S., 1996. Classic British mineral localities: Frongoch Mine, Dyfed. UK Journal of Mines & Minerals, 17, 29-38.
- Wirth, M., 1993. Recent additions (Nos. 1301-1400) to the BMS collection. British Micromount Society Newsletter, No. 35, 15-16.