Crystal System: Trigonal
Status of Occurrence: Confirmed Occurrence
Distribution: Rare
Chemical Composition: Lead iron arsenate hydroxide
Chemical Formula: Pb(Fe3+)3AsO4(AsO3OH)(OH)6
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).


  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.