Arsentsumebite

Crystal System: Monoclinic
Status of Occurrence: Confirmed Occurrence - 2nd UK recording
Distribution: Rare
Chemical Composition: Lead copper arsenate sulphate hydroxide
Chemical Formula: Pb2Cu(AsO4)(SO4)(OH)
Method(s) of Verification: Dolyhir Quarry - XRD and EDS at Manchester Museum (X-ray reference MANCH:XRD1297).

Chemical Group:

  • Arsenates
  • Sulphates

Geological Context:

  • Supergene: in situ natural oxidation & weathering deposits
Pale green arsentsumebite microcrystals to 0.05 mm in length from Dolyhir Quarry. Photo D.I. Green, © D.I. Green.
Scanning electron micrograph of a small fragment (from National Museum of Wales specimen NMW 2007.1G.M.1) bearing blocky arsentsumebite crystals from Dolyhir Quarry. Image D.I. Green, © D.I. Green.
Introduction: a rare secondary mineral formed in the oxidation zone of hydrothermal polymetallic ore deposits.
Occurrence in Wales: discovered recently forming drusy crusts of blocky pale mint green crystals up to 0.1 mm on edge on oxidized lead- and copper-rich veinstone collected from Dolyhir Quarry in the mid-1990s (Hubbard et al., 2007).

Key Localities:

  • Dolyhir Quarry, Old Radnor, Powys: a recent addition to the list of unusual species that occur at this quarry. Arsentsumebite has only been found on a few small fragments of oxidized galena-tennantite-bearing veinstone collected during the mid-1990s.

References:

  1. Cotterell, T.F., Green, D.I., Hubbard, N., Mason, J.S., Starkey, R.E. and Tindle, A.G., 2011. The Mineralogy of Dolyhir Quarry, Old Radnor, Powys, Wales. UK Journal of Mines and Minerals, 32, 5-61.
  2. Hubbard, N., Green, D.I. and Cotterell, T.F., 2007. Arsentsumebite from Dolyhir Quarry, Old Radnor, Powys. UK Journal of Mines and Minerals, 28, 9-10.