Mineral Database

Mineral Database
Mineralogy of Wales

Palygorskite

Crystal System: Monoclinic
Formula: (Mg,Al)2Si4O10(OH).4H2O
Status of Occurrence: Confirmed Occurrence
Distribution: Uncommon
Chemical Composition: Magnesium aluminium silicate hydroxide hydrate
Method(s) of Verification: Mwyndy Mine - XRD (Natural History Museum, in Criddle & Symes, 1977); Ty-coch - XRD (Natural History Museum, in Criddle & Symes, 1977).

Palygorskite 'mountain leather' from Llantrisant, South Wales. Specimen 11.5 x 6 cm. National Museum of Wales Collection (NMW 25.554.GR6.1). Photo M.P. Cooper, © National Museum of Wales.

Chemical Group:
  • Silicates
Geological Context:
  • Hydrothermal
Introduction:

palygorskite, also known by the informal name 'mountain leather', forms in a variety of environments, such as hydrothermal deposits, soils and as slicken sides on fault planes. Although it can form quite large crystals it more commonly occurs as leathery-looking masses.

Occurrence in Wales:

Vivian (1887) reported the presence of 'mountain leather' associated with the hematite deposits of South Wales, but stated no specific locality details. North (1916) stated that mountain leather had been found at Mwyndy Mines, near Llantrisant, South Wales and Criddle & Symes (1977) subsequently recorded palygorskite from Ty-coch.

Key Localities:
  • Mwyndy Mine, Llantrisant, South Wales: North (1916) noted mountain leather had been found with iron ore at this locality and that a small piece had been added to the collections of the National Museum of Wales. Although several specimens are labelled as originating from Llantrisant none is labelled Mwyndy Mine.
  • Ty-coch, near Porthcawl, South Wales: fibrous, white and grey palygorskite was found by Criddle & Symes (1977) at this locality as a coating to shear surfaces in manganese ore (e.g. National Museum of Wales specimen no. NMW 76.22G.M.2).
References:
  • Criddle, A.J., & Symes, R.F., 1977 Mineralization at Ty-coch, Glamorgan (Mid Glamorgan), Wales: the second occurrence of pyrobelonite. 

    Mineralogical Magazine, 41, 85-90.

  • North, F.J., 1916 The minerals of Glamorgan.  Transactions of the Cardiff Naturalists' Society, 49, 16-51.
  • Vivian, S., 1887 The hematite deposits of the southern outcrop of the Carboniferous Limestone of South Wales  Transactions of the Cardiff Naturalist's Society, 19, 48-53.