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Cymraeg

Phosgenite

Crystal System: Tetragonal
Status of Occurrence: Confirmed Occurrence
Distribution: Rare
Chemical Composition: Lead carbonate chloride
Chemical Formula: Pb2CO3Cl2
Method(s) of Verification: Cwmavon Valley Copper Smelting Slags - XRD (Natural History Museum, film no. 12022); Eaglebrook Mine - visual, based on the distinctive morphology of phosgenite crystals; Penrhyn Du - XRD (Dr. P.A. Williams).

Geological Context:

Scanning electron micrograph of tabular phosgenite crystals lining a cavity in weathered galena from Penrhyn Du, Ll?n. National Museum of Wales specimen (NMW 98.16G.M.118). © National Museum of Wales.
Introduction: phosgenite is a secondary lead mineral typically developed in the oxidized zone of lead-bearing ore bodies and through post-mining oxidation of lead-bearing veinstone and metalliferrous slags, particularly where there is prolonged contact with sea water.
Occurrence in Wales: in Wales phosgenite is restricted to a small number of dominantly post-mining occurrences where, crystals are small and inconspicuous except to the trained eye. Hubbard (1991) provided the first account of phosgenite in Wales describing, prismatic and tabular microcrystals on loose blocks of galena-rich veinstone, below high water in a gulley beneath the Penrhyn Du Mine on the Llŷn. Smaller tabular crystals are reported in-situ where the vein outcrops with the sea. In actual fact, phosgenite was known from Wales since 1964 when, R.S.W. Braithwaite collected a specimen from dumps near Halkyn in Flintshire (Bevins, 1994). Phosgenite has since been discovered to a limited extent at Eaglebrook Mine in the Central Wales Orefield (Rust et al., 1995), and a recent investigation by Plant (2003) into the mineralogy of copper smelter slag in the Cwmavon Valley, South Wales has identified minute (0.15 mm) phosgenite crystals, perched on the slag surface.

Key Localities:

There are no key localities for this specimen.

References:

  1. Bevins, R.E., 1994. A Mineralogy of Wales National Museum of Wales, Geological Series No. 16, Cardiff, 146pp.
  2. Hubbard, N., 1991. Phosgenite, the first Welsh occurrence. Journal of the Russell Society, 4 (1), 35.
  3. Plant, S., 2003. Secondary minerals from the Cwmavon Valley Copper Smelting Slags, Glamorgan, South Wales. Journal of the Russell Society, 8(1), 9-15.
  4. Rust, S., Burchmore, S. & Foy, E., 1995. Some interesting new finds from the Nant-y-cagle mine. British Micromount Society Newsletter, 40, 8-10.

There are no references for this specimen.