Hydrocerussite

Crystal System: Trigonal
Status of Occurrence: Confirmed Occurrence
Distribution: Rare
Chemical Composition: Lead carbonate hydroxide
Chemical Formula: Pb3(CO3)2(OH)2
Method(s) of Verification: Dylife Mine - XRD (NHM, 5957F); Esgair Hir Mine - XRD (NMW X-1048 & NHM, 5141F, 7127F & 7250F); Frongoch Mine - XRD (NHM, 8648F); Logaulas Mine - XRD (NMW X-1315); Llechweddhelyg Mine - XRD (NHM, 7782F).

Chemical Group:

  • Carbonates

Geological Context:

  • Supergene: post-mining oxidation & weathering deposits
  • Supergene: in situ natural oxidation & weathering deposits
Pearly white platy hydrocerussite crystals forming a crust, from Grogwynion Mine, in the Central Wales Orefield. National Museum of Wales Collection (NMW 98.35G.M.783). Photo T.F. Cotterell, © National Museum of Wales.
Pearly white, acicular, hydrocerussite microcrystals from Frongoch Mine in the Central Wales Orefield. Specimen and photo S.A. Rust. © S.A. Rust.
A stepped, and somewhat elongated hydrocerussite crystal, from Esgair Hir Mine in the Central Wales Orefield. Specimen and photo S.A. Rust. © S.A. Rust.
Introduction: hydrocerussite is an uncommon secondary mineral found with other lead-bearing minerals in the oxidized zone of lead-bearing orebodies and within mine dumps environments.
Occurrence in Wales: the earliest mention of hydrocerussite from Wales is that of a specimen in the collection of Thomas Pennant (1726-1798) now in the Natural History Museum, London (No. B.M. 1913, 69). The specimen labelled hydrocerussite and said to be from Halkin, Flintshire is undoubtedly from the Mendip Hills, Somersetshire according to L. J. Spencer, the former Keeper of Mineralogy at the Natural History Museum in 1913. It was not until the 1990s that, with the increased popularity of micromineralogy hydrocerussite was discovered as a post-mining phase within lead-rich spoil derived from mining in the Central Wales Orefield.

Key Localities:

  • Darren Mine, Pen-bont Rhydybeddau, Ceredigion: a temporary in-situ exposure created during stope-capping activities in 1992 revealed hydrocerussite (Bevins & Mason, 1997).
  • Dylife Mine, Penegoes, Powys: originally described by Rust & Rust (1987) as Dyfngwm Mine, the westernmost workings of Dylife Mine on Pen Dylife Lode consist of a number of heavily weathered mine dumps. Post-mining alteration of lead-bearing veinstone has resulted in the formation of hydrocerussite as very rare zoned prismatic crystals ranging in colour from creamy to white and colourless. Crystals form divergent masses to 0.8 mm. Individually the crystals display a triangular cross-section with concave prismatic faces (Rust & Rust, 1987).
  • Esgairhir Mine, Tal-y-bont, Ceredigion: four different forms are recorded by Rust & Mason (1988) including, divergent fan-like crystal sprays, pearly white coatings, flattened hexagonal crystals with very shallow pyramid faces and triangular-section prismatic crystals occasionally showing concave prism faces. Crystals reach 0.5 mm in length with colour varying from colourless to white and cream with some stained green and blue.
  • Frongoch Mine, Devil's Bridge, Ceredigion: groups of creamy-white acicular crystals to 0.7 mm, and thin, tabular, crudely hexagonal crystals to 0.4 mm occur rarely, forming extensive pearly coatings on galena-cerussite matrix (Green et al., 1996). Associated species include susannite and caledonite.
  • Halkyn, Flintshire: a specimen labelled hydrocerussite from Halkin, Flintshire is in the collection of Thomas Pennant (1726-1798), but is believed to be from the Mendip Hills, Somerset and should therefore be regarded as dubious.
  • Llechweddhelyg Mine, Penrhyncoch, Ceredigion: listed by Bevins & Mason (1997).
  • Logaulas Mine, Ysbyty Ystwyth,Ceredigion: minute fibrous white overgrowth on cerussite collected from dumps near to the opencut (National Museum of Wales collections).
  • Nant Melyn Mine, Hafren Forest, Powys: rare hydrocerussite (Bevins & Mason, 1997) occurs as part of a dump-formed secondary assemblage.

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. 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.
  3. Rust, S. & Rust, D., 1987. Micro-minerals from Dyfngwm Mine. U.K. Journal of Mines and Minerals, No. 2, 28-32.
  4. Rust, S.A. & Mason, J.S., 1988. The minerals of Esgair-Hir mine, Dyfed, Wales. UK Journal of Mines & Minerals, 5, 35-43.

There are no references for this specimen.