Mineral Database

Mineral Database
Mineralogy of Wales

Segnitite

Crystal System: Trigonal
Formula: Pb(Fe3+)3AsO4(AsO3OH)(OH)6
Status of Occurrence: Confirmed Occurrence
Distribution: Rare
Chemical Composition: Lead iron arsenate hydroxide
Method(s) of Verification: Dolyhir Quarry: XRD at the National Museum of Wales (numbers NMW X-1440, X-1441 and X-1444).
Chemical Group:
  • Arsenates
Geological Context:
  • Supergene : in situ natural oxidation & weathering deposits
Introduction: a rare secondary mineral species found in the near surface (supergene) oxidation zone of lead- and arsenic-bearing primary sulphide deposits. Segnitite forms a solid-solution series with beudantite, Pb(Fe3+)3(AsO4)(SO4)(OH)6, from which it is difficult to distinguish.
Occurrence in Wales: segnitite was identified by Cotterell et al. (2011) as a component of supergene mineralization derived from the oxidation of a primary galena-tennantite-chalcopyrite vein cutting through limestone of Silurian age.
Key Localities:
  • Dolyhir Quarry, Old Radnor, Powys: yellow, yellow-green and greenish brown crusts of powdery, microcrystalline segnitite occur with anglesite on highly oxidized chalcopyrite-tennantite-galena vein material collected during the mid-1990s (Cotterell et al., 2011).
References:
  • 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.