Mineral Database (Saesneg yn unig)

Mineral Database (Saesneg yn unig)
Mineralogy of Wales

Aleksite

Crystal System: Trigonal
Formula: PbBi2Te2S2
Status of Occurrence: Confirmed Occurrence - 1st UK recording
Distribution: Rare
Chemical Composition: Lead bismuth sulphotelluride
Method(s) of Verification: Clogau Mine - XRD & EMPA (Natural History Museum, X-ray reference numbers, 8028F & 8044F, described as 'aleksite or near').
Chemical Group:
  • Sulphides
Geological Context:
  • Hydrothermal : mesothermal polymetallic veins
Introduction: aleksite is an exceedingly rare mineral, only known from a very limited number of samples obtained from bismuth telluride assemblages. Very fine-grained, it is unlikely to be noticed in hand specimen and its identification requires ore petrology backed up by SEM analytical facilities. Associated minerals include other bismuth tellurides, galena and gold.
Occurrence in Wales: aleksite was identified in a telluride-rich sample collected from Clogau Gold Mine in North Wales in the early 1980s (Bevins & Stanley, 1990). This represented only the second occurrence of the mineral worldwide.
Key Localities:
  • Clogau Mine, Bontddu, Gwynedd: silvery-grey blade-like masses to 200 µm, intergrown with galena and tellurobismuthite in quartz (Bevins & Stanley, 1990).
References:
  • Bevins, R.E. & Stanley, C.J., 1990 Aleskite, a lead bismuth sulfotelluride: a second world occurrence from the Dolgellau Gold Belt, Gwynedd, Wales.  Journal of the Russell Society, 3, 67-69.