Cerussite

Crystal System: Orthorhombic
Status of Occurrence: Confirmed Occurrence
Distribution: Locally Abundant
Chemical Composition: Lead carbonate
Chemical Formula: PbCO3
Method(s) of Verification: many of the cited examples have been confirmed by XRD at the National Museum of Wales or the Natural History Museum. Some examples include Sigenlas (NMW X-1087) & Eaglebrook (NMW X-1154) mines in Central Wales and Cyffty Mine (NMW X-994) nr. Llanrwst.

Geological Context:

  • Supergene: post-mining oxidation & weathering deposits
  • Supergene: in situ natural oxidation & weathering deposits
Reticulated cerussite from Frongoch Mine, in the Central Wales Orefield. S.A. Rust Collection. Photo D.I. Green, © National Museum of Wales.
Gemmy colourless cerussite crystals, 1-2 mm across, on iron-rich matrix from Rhyd Fach Mine, in the Central Wales Orefield. J.S. Mason Collection (no. JMRF003). Photo M.P. Cooper, © National Museum of Wales.
Jackstraw cerussite crystals, to 2 mm, from Dolyhir Quarry. N. Hubbard Collection. Photo D.I. Green. © D.I. Green.
Introduction: cerussite is a common secondary mineral in the oxidized zone of lead-bearing veins, usually as a coating on galena.
Occurrence in Wales: cerussite is a common mineral in Wales having been known from the principality from the late 18th Century. Thomas Pennant (1726-1798) recorded cerussite from Flintshire as early as 1778 (Campbell Smith, 1913). Some of the finest examples have been collected from mines in the Central Wales Orefield, in particular the Lisburne mines (Logaulas and Frongoch). The dominant habit is tabular crystals, although acicular crystals are known from Eaglebrook Mine. In South Wales, cerussite is uncommon, occurring in small quantities in lead veins cutting Carboniferous limestone, particularly in the area surrounding Machen. Good crystals have been recovered from Machen Quarry, but anglesite is far more abundant.

Key Localities:

  • Aberdaunant Mine, Llanidloes, Powys: considerable amounts of cerussite are described from the dumps by Jones (1922). Specimens typically show flat-lying platy crystals (National Museum of Wales Mineral Collection, NMW 27.111.GR.389) in association with weathered goethite-coated galena cubes.
  • Bodcoll Mine, Devil’s Bridge, Ceredigion: abundant cerussite-rich gossan, but restricted to small crystals (T.F. Cotterell, unpublished data).
  • Bog Mine, Ponterwyd, Ceredigion: cerussite is common as weathered crusts of opaque white crystals on the dumps derived from outcrop workings. Occasional fine gemmy tabular crystals (to 4 mm) occur within cavities (T.F. Cotterell, unpublished data).
  • Bwlch-glas Mine, Tal-y-bont, Ceredigion: Braithwaite (1982) described three modes of cerussite from Bwlch-glas. These include platy crystals lining fracture surfaces; recent, stalactitic rippled “flowstone” on adit walls, consisting of masses of friable microcrystals and; clear, individual crystals associated with fine-grained pyromorphite and wulfenite from one small cavity. Interestingly no cerussite has been recorded from the breccia pipe where the coarse pyromorphite dominates.
  • Cyffty Mine, Llanrwst, Gwynedd: greyish acicular crystals to several centimetres long, spanning cavities in and on the surface of highly friable veinstone occur on specimens formerly in the collection of G.J. Williams, the former Mine Inspector for North Wales. These specimens are now in the National Museum of Wales Mineral Collection (NMW 27.111.GR.396, 397 & 411).
  • Dolgellau Gold-belt, Gwynedd: Readwin (1888) listed cerussite from the Dolgellau Gold-belt, although no specific locality details were presented. There is a distinct paucity of secondary minerals from the Dolgellau Gold-belt and as such any specimens are likely to have been relatively small.
  • Dylife Mine, Penegoes, Powys: Jones (1922) recorded cerussite on dumps following the outcrop of the Dyfngwm Lode on Pen Dylife, while well-crystallized specimens have been collected from dumps above the Gwaith Gwyn adit (T.F. Cotterell, unpublished data).
  • Eaglebrook (Nantycagl) Mine, Ceulanymaesmawr, Ceredigion: cerussite is fairly common at Eaglebrook, the most common habit being acicular ‘jackstraw’ bunches. Some of the larger crystals (which may reach 20 mm) show alteration to linarite and often have iron staining.
  • Esgairhir Mine, Tal-y-bont, Ceredigion: rich crystalline masses have been found on one section of the mine dumps. A specimen in the National Museum of Wales Mineral Collection (NMW 74.27G.M.12), acquired from the D.B. Hardman Collecion (No. 443) exhibits twinned crystals to 5 mm, in iron-rich gossan. Abundant pink crystalline crusts are noted by Jones & Moreton (1977).
  • Frongoch Mine, Devil's Bridge, Ceredigion: cerussite is very common at Frongoch and was noted by Greg & Lettsom in 1858. Frongoch is famous for both reticulated crystals and large tabular crystals. Some of the richest examples known, were collected during recent excavations of dump material. These include tabular crystals exceptionally to 30 mm long.
  • Gorlan Mine, Trefriw, Gwynedd: single snow-white acicular crystals, up to 8 mm long, span cavities in weathered galena on National Museum of Wales specimen NMW 27.111.GR.395.
  • Halkyn District, Flintshire: cerussite was recorded from the Halkyn District by Thomas Pennant in 1778 (Pennant, 1778). Although rarely crystallized, Pennant had specimens from Crecas, ‘Claudh Mine, Silver Rake and Talacre Mine (Campbell Smith, 1913). Specimens in the National Museum of Wales Mineral Collection from North Hendre, Caeau and Rhosesmor mines (NMW 27.111.GR.391, 393 & 394 respectively) display similar massive cerussite. A little to the south Greg & Lettsom (1858) noted cerussite at Jamaica Mine.
  • Henfwlch Mine, Ceulanymaesmawr, Ceredigion: occasional small acicular cerussite crystals span cavities within veinstone on surface dumps and underground small platy crystals are seen within cavities in veinstone (T.F. Cotterell, unpublished data).
  • Llanrwst Mine, Llanrwst, Gwynedd: Captain Borlase collected cerussite in 1889, forming an aggregate of powdery, white acicular crystals. Borlase’s original specimen is now housed in the National Museum of Wales Mineral Collection (NMW 85.70G.M.33) having passed through the collections of W.T. Shaw and R.W. Barstow.
  • Llechweddhelyg Mine, Penrhyncoch, Ceredigion: cerussite forms an important component of the rich gossan encountered in the eastern engine-shaft. Solid masses to 4 cm across have been collected with malachite in goethitic gossan. Occasional large tabular crystals occur on massive quartz. Small twinned crystals occur occasionally (Jones, 1987). Barite was reported during the sinking of the eastern engine-shaft (Mining Journal, 1856). No barite has been witnessed on the surrounding dumps and it is likely that this report refers to bladed cerussite present within the gossan encountered during sinking of the shaft.
  • Logaulas Mine, Ysbyty Ystwyth,Ceredigion: described by Greg & Lettsom (1858) as forming ‘in magnificent translucent tabular crystals’, as testified by a specimen in the NHM Mineral Collection. According to Jones (1922) cerussite occurs in some abundance in gossan in the Logaulas Lode. Good quality tabular crystals and occasional sixling twins (up to 8 mm) have been collected from opencast workings, particularly from the 1960s onwards, but not of the quality seen during active mining. The National Museum of Wales houses a number of rich specimens, displaying bleached mudstone densely covered by tabular cerussite (to 5 mm) in areas in excess of 6 x 6 cm.
  • Machen Quarry, Caerphilly, South Wales: described by Plant & Jones (1995) as ‘occasionally common’. Cerussite occurs both within cavities in weathered galena veins and rarely in small cavities in dolomitized limestone around the margins of the quarry. Crystals typically show a tabular to blocky form.
  • Nant Mine, Llangunnor, Carmarthenshire: blocky jackstraw crystals span small (< 10 mm) cavities within barite veinstone on National Museum of Wales specimens, including NMW 83.40G.M.26.
  • Nant-y-mwyn Mine, Rhandirmwyn, Carmarthenshire: very fine, hair-like acicular crystals form a dense web-like growth, spanning solution cavities within quartz veinstone, particularly on National Museum of Wales specimen NMW 76.4G.M.1.
  • Penycefn Mine, Bontgoch, Ceredigion: a considerable amount of cerussite was encountered in a cross-cut southward from the east end of the Penycefn workings and in outcrop south of the cross-cut (Jones, 1922).
  • Rhydfach adit, Tal-y-bont, Ceredigion: Mason (1994) described cerussite locally forming well-developed crystals up to 2 mm in size at the western end of the adit level. Gemmy transparent microcrystals richly coat friable quartz veinstone derived from the back of the adit.
  • Vale of Towy Mine, Llandeilo, Carmarthenshire: rich, friable crystallized cerussite flowstone from underground workings as shown by National Museum of Wales specimen NMW 2004.27G.M.1.
  • Welsh Foxdale (New Pandora) Mine, Trefriw, Gwynedd: Prior (1906) reported cerussite from the 23 ft. level, Francis Lode, forming long prismatic crystals associated with dundasite and allophane.Very distinctive aggregates of ‘jack-straw’ acicular crystals (NMW 27.111.GR.400) and massive, porous, chalky-white cerussite is present (NMW 27.111.GR.398) on specimens in the National Museum of Wales Mineral Collection.

There are no key localities for this specimen.

References:

  1. 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.
  2. Braithwaite, R.S.W., 1982b. Pyromorphite, wulfenite and other minerals from Bwlch-Glas mine, Central Wales. Mineralogical Record, 13, 151-153.
  3. Campbell Smith, W., 1913. The mineral collection of Thomas Pennant (1726-1798). Mineralogical Magazine, 16, 331-342.
  4. 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.
  5. Greg, R.P. & Lettsom, W.G., 1858. Manual of the Mineralogy of Great Britain and Ireland. John van Voorst, London, 483pp.
  6. Jones, A.D., 1987. The Minerals of Llechwedd Helyg. UK Journal of Mines and Minerals. 3, 25-27.
  7. Jones, J.A. & Moreton, N.J.M., 1977. The Mines and Minerals of Mid-Wales 40pp.
  8. Jones, O.T., 1922. Lead and zinc. The mining district of North Cardiganshire and West Montgomeryshire. Memoirs of the Geological Survey. Special Report of the Mineral Resources of Great Britain, 20.
  9. Mason, J.S., 1994. A Regional Paragenesis for the Central Wales Orefield. Unpublished M.Phil thesis, University of Wales (Aberystwyth).
  10. Pennant, T., 1778. Tour in Wales.
  11. Plant, S.P. & Jones, I.E., 1995. Minerals of Machen Quarry, Mid Glamorgan, Wales. Journal of the Russell Society, 6(1), 31-36.
  12. Prior, G.T., 1906. Dundasite from North Wales. Mineralogical Magazine, 14, 167-169
  13. Readwin, T.A., 1888. Gold in Wales. London, 12pp.

There are no references for this specimen.