Stibnite

Crystal System: Orthorhombic
Status of Occurrence: Confirmed Occurrence
Distribution: Locally Abundant
Chemical Composition: Antimony sulphide
Chemical Formula: Sb2S3
Method(s) of Verification: Bwlch Mine - XRD & EMPA (Bevins et al., 1988)

Chemical Group:

  • Sulphides

Geological Context:

  • Hydrothermal: epithermal polymetallic veins & pipes
Steel-grey stibnite in Ordovician rhyolitic ignimbrite from Bwlch Mine. Specimen 11 cm x 6 cm, National Museum of Wales collection (NMW 85.70G.M.34), ex R.W. Barstow. © National Museum of Wales.
Introduction: stibnite may occur in a variety of hydrothermal mineral deposits, but is most frequently found in low-temperature assemblages where it may be associated with galena, pyrite, antimony sulphosalts and gold. It may also occur in hot spring or fumarolic deposits with realgar, sulphur and other minerals. Stibnite is distinctive when coarse-grained but fine-grained occurrences can easily be confused with a plethora of lead-antimony (Pb-Sb) sulphosalt minerals: in such cases analytical determinations are required for positive identification.
Occurrence in Wales: stibnite, with a range of lead-antimony sulphosalts, was mined at Bwlch, near Deganwy in North Wales, the site of Wales's only antimony mine. Little is known of its history, except that Bick (1985) notes that the site was marked as an antimony mine on a map dated 1837. The site was investigated by Russell (1944) who noted some accompanying Pb-Sb sulphosalts, which were confirmed and added to in terms of species by Bevins et al (1988). Two other supposed occurrences of stibnite, one from the shore between Rhos-Y-Mynach and Dulas in north-east Anglesey (National Museum of Wales specimen, ex G.J. Williams collection) and the other from the Dolgellau Gold-belt (Readwin, 1988) remain unverified.

Key Localities:

  • Bwlch Mine, Deganwy, Gwynedd: stibnite forms coarsely bladed masses to several centimetres in size, accompanied by Pb-Sb sulphosalts and minor galena and sphalerite in numerous quartz veinlets which irregularly cut a mass of highly altered nodular ignimbrite of Middle Ordovician age. The geological setting and mineral association suggest that this is an epithermal deposit, probably related to near-surface hydrothermal activity during Middle Ordovician volcanism.

There are no key localities for this specimen.

References:

  1. Bevins, R.E., Alderton, D.H.M. & Horak, J.M., 1988. Lead-antimony mineralisation at Bwlch Mine, Deganwy, Wales. Mineralogical Magazine, 52, 391-394.
  2. Bick, D.E., 1982. The Old Copper Mines of Snowdonia. Second Edition. Pound House, Newent.
  3. Russell, A., 1944. Notes on some minerals either new or rare in Britain. Mineralogical Magazine, 27, 1-10.

There are no references for this specimen.