Crystal System: Monoclinic
Status of Occurrence: Confirmed Occurrence - 1st UK recording
Distribution: Rare
Chemical Composition: Hydrated iron sulphate
Chemical Formula: Fe2+SO4.H2O
Method(s) of Verification: Ebbw Vale Return - XRD at the Natural History Museum, London (XRD no. x1623); Parys Mountain and Trwyn Cae Iago - XRD at the National Museum of Wales (XRD numbers NMW X-859 and NMW X-1938 respectively).

Geological Context:

  • Supergene: post-mining oxidation & weathering deposits
Introduction: szomolnokite is a secondary sulphate typically found in highly acidic mine environments associated with oxidizing pyrite.
Occurrence in Wales: Bevins (1988) produced the first verified account of szomolnokite in the British Isles, from Crumlin Colliery, Ebbw Vale in Gwent. White, powdery efflorescence on a couple of specimens in the mineral collection of the Natural History Museum proved upon X-ray diffraction analysis to be the rare hydrated iron sulphate, szomolnokite. Further occurrences are described by Cotterell (2009) at Parys Mountain, Anglesey and Trwyn Cae Iago, near Porthmadog, Gwynedd, north Wales both in association with other iron sulphates, including halotrichite.

Key Localities:

  • Crumlin Colliery, Ebbw Vale, Gwent: white, powdery efflorescence (Bevins, 1994) on, Natural History Museum specimens B.M. 1985,MI 33592 and B.M. 1985,MI 33593 from Seam ‘x’, Ebbw Vale Main, and ‘40 yd outbye 1st ¾ crosscut on Ebbw Vale Return’ are described by Bevins (1988).
  • Parys Mountain, Anglesey: beige coloured powdery szomolnokite occurs in association with silky white fibrous halotrichite on National Museum of Wales specimen, no. NMW 75.38G.M.5, labelled as 'Main Lode, Parys Mountain' (Cotterell, 2009).
  • Trwyn Cae Iago, near Porthmadog: Cotterell (2009) identified a beige coloured powdery phase in association with white fibrous halotrichite and yellow jarosite on National Museum of Wales specimen no. NMW 79.10G.M.2 as szomolnokite.


  1. Bevins, R.E., 1994. A Mineralogy of Wales National Museum of Wales, Geological Series No. 16, Cardiff, 146pp.
  2. Bevins, R.E., 1988. Sixth supplementary list of British Isles minerals (Welsh). Mineralogical Magazine, 52, 121-124.
  3. Cotterell, T.F., 2009. A review of halotrichite group minerals in Wales. UK Journal of Mines and Minerals, 30, 43-47.