Mineral Database

Mineral Database
Mineralogy of Wales

Dundasite

Crystal System: Orthorhombic
Formula: PbAl2(CO3)2(OH)4.H2O
Status of Occurrence: Confirmed Occurrence - 1st UK recording
Distribution: Rare
Chemical Composition: Lead aluminium carbonate hydroxide hydrate
Method(s) of Verification: Cyffty Mine - verification method uncertain; Eaglebrook Mine - XRD (Natural History Museum, London, X-ray no. 6081F); Gorlan Mine - verification method uncertain; Welsh Foxdale Mine - wet chemical analysis & visual comparision with type material.

Dundasite from Cyffty Mine, minute spherical crystals (up to 0.5 mm across) associated with cerussite. Specimen National Museum of Wales (NMW 27.111.GR.410), ex G.J. Williams Collection. Photo M.P. Cooper, © National Musuem of Wales.

Dundasite on cerussite from New Pandora Mine, Llanrwst. Specimen National Museum of Wales (NMW 27.111.GR.407). Photo M.P. Cooper, © National Museum of Wales.

Chemical Group:
  • Carbonates
Geological Context:
  • Supergene : in situ natural oxidation & weathering deposits
  • Supergene : post-mining oxidation & weathering deposits
Introduction: dundasite is a secondary mineral found in the oxidized portions of lead-bearing ore deposits. It occurs late in secondary parageneses.
Occurrence in Wales: the first British occurrence of dundasite was made by Prior (1906) on specimens from Welsh Foxdale Mine near Trefriw in Gwynedd. The original discovery was made by G.J. Williams, H.M. Inspector of Mines for North Wales, who noted the small tufts as a mineral unknown to him. Subsequently G.J. Williams discovered dundasite at two further mines in the Llanrwst area. Later, dundasite was recorded as one of a suite of unusual secondary lead species occurring within weathered mine tips in Central Wales, most probably post mining in origin.
Key Localities:
  • Cyffty Mine, Llanrwst, Gwynedd: Russell (1944) reported receiving a remarkably good specimen of dundasite from G.J. Williams, H.M. Inspector of Mines for North Wales, in May 1920. Dundasite, forming snow-white spheres up to 1 mm in diameter occurs on long acicular cerussite crystals overgrowing quartz-lined solution cavities after marcasite and sphalerite.
  • Eaglebrook (Nantycagl) Mine, Ceulanymaesmawr, Ceredigion: Small balls of radiating acicular crystals up to 0.5 mm in diameter found on two specimens of limonitic matrix with associated anglesite and linarite. The spherules vary in colour from very pale blue at their centres to white at their terminations (British Micromount Society Newsletter no. 19).
  • Gorlan Mine, Trefriw, Gwynedd: Dundasite forms snow-white downy crusts on brownish-yellow gum-like allophane which itself coats prismatic cerussite and bipyramidal quartz crystals (Russell, 1944). Dundasite was, again, the last secondary mineral to form.
  • Welsh Foxdale (New Pandora) Mine, Trefriw, Gwynedd: Small, silky, white tufts on cerussite from the 23 ft. level on Francis Lode (Prior, 1906). Small, glassy spherules of allophane occur in association.
References:
  • Prior, G.T., 1906 Dundasite from North Wales.  Mineralogical Magazine, 14, 167-169
  • Russell, A., 1944 Notes on some minerals either new or rare in Britain.  Mineralogical Magazine, 27, 1-10.