Crystal System: Trigonal
Status of Occurrence: Confirmed Occurrence - 1st UK recording
Chemical Composition: Lead bismuth sulphotelluride
Chemical Formula: PbBi2Te2S2
Method(s) of Verification: Clogau Mine - XRD & EMPA (Natural History Museum, X-ray reference numbers, 8028F & 8044F, described as 'aleksite or near').
- 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.
- Clogau Mine, Bontddu, Gwynedd: silvery-grey blade-like masses to 200 µm, intergrown with galena and tellurobismuthite in quartz (Bevins & Stanley, 1990).
- 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.