Crystal System: Cubic
Status of Occurrence: Confirmed Occurrence - 2nd UK recording
Distribution: Rare
Chemical Composition: Hydrated ammonium-aluminium sulphate
Chemical Formula: NH4Al(SO4)2.12H2O
Method(s) of Verification: Two-Feet-Nine Seam, Deep Navigation Colliery, Treharris - identified by XRD at the National Museum of Wales (XRD no. NMW X-1944).

Chemical Group:

  • Sulphates
Introduction: an uncommon secondary sulphate mineral in some coal deposits or as efflorescence associated with fumaroles and hot springs.
Occurrence in Wales: colourless crystallized tschermigite was identified on a specimen of epsomite from Deep Navigation Colliery during a study of halotrichite group minerals from Wales (Cotterell, 2009).

Key Localities:

  • Deep Navigation Colliery, Treharris, South Wales: colourless crystallized tschermigite occurs intergrown with massive opaque white epsomite on a specimen from the Two-Feet-Nine Seam, Deep Navigation Pit donated by T. Gwilt Cotsworth to the National Museum of Wales specimen in 1927 and accessioned as NMW 27.128.GR.2 (Cotterell, 2009).


  1. Cotterell, T.F., 2009. A review of halotrichite group minerals in Wales. UK Journal of Mines and Minerals, 30, 43-47.