Mineral Database (Saesneg yn unig)

Mineral Database (Saesneg yn unig)
Mineralogy of Wales

Anglesite

Crystal System: Orthorhombic
Formula: PbSO4
Status of Occurrence: Confirmed Occurrence - Type Locality In Wales
Distribution: Locally Abundant
Chemical Composition: Lead sulphate
Method(s) of Verification: Parys Mountain - XRD at the Natural History Museum, London; Central Wales Orefield - many localities by XRD including Cwmystwyth, Dylife, Eaglebrook, Esgairhir & Frongoch (all at the NHM, London); Dolyhir Quarry - XRD (Manchester Museum).
Chemical Group:
  • Sulphates
Geological Context:
  • Supergene : post-mining oxidation & weathering deposits
  • Supergene : in situ natural oxidation & weathering deposits
Introduction:

anglesite occurs in the oxidation zones of lead-bearing ore deposits. It forms early during the galena alteration process, in relatively acidic conditions where fluid circulation is restricted. In more open systems, carbonate ions contributed by dissolved CO2 in rainwater raise the pH beyond that where anglesite is stable and the much commoner lead carbonate, cerussite, forms instead. Similar micro-environments occur within mine spoil and anglesite is not uncommon as a post-mining mineral, often in association with covellite and linarite. The name anglesite is derived from Anglesey, the island in North Wales upon which the mineral was first discovered - at Parys Mountain.

Occurrence in Wales:

Although named by Beudant (1832), the existence of this mineral, previously known as 'vitriol de plomb', at Parys Mountain had been known for many years. It was, for example, mentioned by Monnet (1779). The late 18th Century was the time when the majority of the anglesite specimens from Parys Mountain were obtained, for example specimen 91.6G.M.1 in the National Museum of Wales Collection, which was collected in 1784. These specimens were discovered during removal of the gossan overlying the primary sulphide zone and few have been found since: consequently well-formed Parys Mountain anglesites now command high prices on the mineral specimen market. Other minor occurrences of anglesite in North Wales are from Bwlch Mine, near Deganwy (Russell, 1944), Castell Carn Dochan Mine, near Bala (S.A. Rust Collection) and from Llanengan (XRD record, Natural History Museum, London) and Penrhyn-Du mines on the Llŷn. More recently, anglesite has been identified at a significant number of old lead mines and also at several working quarries across Wales with a nucleus of occurrences, many of the post-mining category, within the Central Wales Orefield. Apart from the more noteworthy occurrences described in detail under 'key localities' below, it has been reported from Bodcoll Mine (Bevins & Mason, 1997), Bwlchrhennaid Mine (British Micromount Society Newsletter 18), Cwmystwyth Mine (Natural History Museum, London, XRD record), Darren Mine (Rust, 1990), Esgairddu Mine (Bevins & Mason, 1997), Esgairmwyn Mine (S.A. Rust Collection), Gellireirin Mine (Bevins & Mason, 1997), Geufron Mine (British Micromount Society Newsletter 15), Glogfawr Mine (British Micromount Society Newsletter 16), Hafan Mine (S.A. Rust Collection), Hendrefelin Mine (S.A. Rust Collection), Henfwlch Mine (T.F. Cotterell, unpublished data), Llettyevan-hen Mine (S.A. Rust Collection), Mynyddgorddu Mine (D.I. Green, unpublished data), South Nantycar Mine (British Micromount Society Newsletter 34), Nantycreiau Mine (T.F. Cotterell, unpublished data), Penpompren Mine (S.A. Rust Collection), Penrhiw Mine (Mason & Green, 1995), Quarry Shaft, Llywernog Mine (S.A. Rust Collection) and Ystrad Einion Mine (Mason & Rust, 1997). In South Wales, some very fine specimens of anglesite were obtained at Machen Quarry in the 1980s (see below) and it has also been recorded from Rhyd-y-Gwern Mine, near Machen (Natural History Museum, London, XRD record) and from Hendy Quarry, Miskin (British Micromount Society Newsletter 35).

Key Localities:
  • Central Wales Orefield: common as microcrystals at many of the mines within this orefield. Notable localities include: Bwlch-glas Mine where, microcrystals of anglesite have been found underground in situ, occurring in cavities in part-oxidized galena (Braithwaite 1982a); Dylife Mine as colourless crystals, up to 1.5 mm in size, associated with linarite, brochantite, lautenthalite and susannite (Rust & Rust 1987); Eaglebrook Mine where anglesite occurs as blocky crystals, exceptionally 7 mm in size, and also as white pseudomorphs after linarite (Braithwaite, 1982b); Esgairhir Mine as thin crusts and euhedral crystals (<1 mm) and pseudomorphs after linarite (Rust & Mason, 1988); Frongoch Mine occasionally as excellent microcrystals from the tips at this site, within which a diverse post-mining supergene mineral assemblage has developed. It forms blocky crystals to 1.5 mm and blades to 3 mm. Associated minerals are covellite, linarite and native sulphur (Green et al., 1996); Llechweddhelyg Mine occasionally as minute gemmy yellow to clear crystals in cavities in part-oxidized galena, or as colourless equant crystals on linarite (Jones, 1987); Nant Melyn Mine some fine microcrystals of anglesite, occurring as gemmy blocky crystals associated with linarite (J.S. Mason, unpublished data).
  • Dolyhir Quarry, Old Radnor, Powys: fine euhedral crystals of anglesite were collected here in the mid-1990s. Of equant habit, occasionally reaching 5 mm in size, they occurred in cavities within massive intergrown galena and tennantite. Associated minerals were bindheimite, sulphur and cerussite.
  • Llangynog Mine, Llangynog, Powys: colorless to white crystals, exceptionally 4 mm across, have occasionally been found in cavities in galena (associated with native sulphur) or in gossan with linarite (Bevins & Mason, 1997).
  • Machen Quarry, Caerphilly, South Wales: some superb and large crystals of anglesite were found at this locality in the 1980s, in cavities in a galena vein exposed by quarrying. Examples from these finds are preserved in the National Museum of Wales Collection (e.g. specimen NMW 85.62G.M.1). Other specimens are known in which anglesite crystals reach over 20 mm in size (I.E. Jones Collection).
  • Parys Mountain, Anglesey: the type locality for anglesite. It occurred (for very little has been found in recent years) as euhedral crystals, white to yellow in colour and translucent to transparent, typically scattered as individuals on brown to greyish gossan matrix. Individual crystals can reach 10 mm in size but 4-5 mm is more typical. The acidic groundwater conditions on Parys Mountain, caused by the abundance of oxidizing pyrite, helped to create conditions in which abundant anglesite was, unusually, deposited in an open but stable environment.
  • Wedding Cave Mine, Bwlchgwyn, Wrexham: anglesite occurs in a complex supergene assemblage associated with cerussite, linarite and carbonate-cyanotrichite (Green, 1995).
References:
  • Beudant, F.S., 1832 Traité élémentaire de Minéralogie. 2nd Edition.  Paris.
  • 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.
  • Braithwaite, R.S.W., 1982b Pyromorphite, wulfenite and other minerals from the Bwlch-Glas mine, Central Wales.  Mineralogical Record, 13, 151-153.
  • Braithwaite, R.S.W., 1982a Wroewolfeite in Britain.  Mineralogical Record, 13, 167-174.
  • Green, D.I., 1995 Carbonate-cyanotrichite from the Wedding Cave mine, Bwlchgwyn, Clwyd.  UK Journal of Mines & Minerals, 15, 19.
  • 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.
  • Jones, A.D., 1987 The minerals of Llechweddhelyg.  U.K. Journal of Mines and Minerals, No. 3, 25-27.
  • Mason, J.S. & Green, D.I., 1995 Supergene minerals including exceptional ramsbeckite from Penrhiw Mine, Ystumtuen, Dyfed.  UK Journal of Mines & Minerals, 15, 21-27.
  • Mason, J.S. & Rust, S.A., 1997 The Mineralogy of Ystrad Einion Mine, Dyfed, Wales.  U.K. Journal of Mines and Minerals, 18, 33-36.
  • Monnet, M., 1779 Nouveau Systême de Minéralogie.  Paris.
  • Russell, A., 1944 Notes on some minerals either new or rare in Britain.  Mineralogical Magazine, 27, 1-10.
  • Rust, S. & Rust, D., 1987 Micro-minerals from Dyfngwm Mine.  U.K. Journal of Mines and Minerals, No. 2, 28-32.
  • Rust, S.A., 1990a Mattheddleite from the Darren Mine, Dyfed, Wales.  UK Journal of Mines and Minerals. 8, 47-48.
  • Rust, S.A. & Mason, J.S., 1988 The minerals of Esgair-Hir mine, Dyfed, Wales.  UK Journal of Mines & Minerals, 5, 35-43.