Mineral Database

Mineral Database
Mineralogy of Wales

Kermesite

Crystal System: Triclinic
Formula: Sb2S2O
Status of Occurrence: Unconfirmed Occurrence
Distribution: Rare
Chemical Composition: Antimony oxysulphide
Method(s) of Verification: visual only.

Steel-grey stibnite, partially altered to cherry-red ?kermesite from Bwlch Mine. Specimen 11 cm x 6 cm. National Museum of Wales Collection (NMW 85.70G.M.34), ex R.W. Barstow Collection. © National Museum of Wales.

Chemical Group:
  • Oxysulphides
Geological Context:
  • Supergene : in situ natural oxidation & weathering deposits
Introduction: kermesite is a cherry-red secondary mineral, typically found as surface alteration of stibnite.
Occurrence in Wales: kermesite has never been fully verified from Wales. Bevins et al. (1988) and Bevins (1994) described possible kermesite from Bwlch Mine, Deganwy, forming cherry-red coatings on stibnite, but failed to confirm this through X-ray diffraction. Similarly cherry-red secondary coatings on a specimen of stibnite reputedly from the north coast of Anglesey have been suggested to be kermesite, but never verified (Bevins, 1994).
Key Localities:
  • Anglesey: a specimen of stibnite in the mineral collection of the National Museum of Wales (NMW 27.111.GR.283), reputedly collected from the coast between Rhôs-mynach Mine and Dulas, on Anglesey has a cherry-red surface coating, that may well be kermesite, but verification has not been made. Further to this, the validity of the provenance of this specimen is questionable as no other antimony-bearing minerals are known from this part of Anglesey (Bevins, 1994).
  • Bwlch Mine, Deganwy, Gwynedd: cherry-red coatings on stibnite have been suggested as kermesite, but have never been verified (Bevins, 1994).
References:
  • Bevins, R.E., 1994 A Mineralogy of Wales  National Museum of Wales, Geological Series No. 16, Cardiff, 146pp.
  • Bevins, R.E., Alderton, D.H.M. & Horak, J.M., 1988 Lead-antimony mineralisation at Bwlch Mine, Deganwy, Wales.  Mineralogical Magazine, 52, 391-394.