Steverustite

Crystal System: Monoclinic
Status of Occurrence: Confirmed Occurrence - Type Locality In Wales
Distribution: Rare
Chemical Composition: Lead copper thiosulphate hydroxide hydrate
Chemical Formula: Pb2+5(OH)5[Cu+(S6+O3S2-)3](H2O)2
Method(s) of Verification: described as a new species from Frongoch Mine on the basis of EMP, IR and XRD data.

Geological Context:

  • Supergene
Introduction: an unusual post-mining supergene mineral formed during oxidation of galena-bearing veinstone within mine dumps. Steverustite typically forms colourless to white, lath-like crystals that aggregate to form fibrous fan-like bundles to 1.5 mm across. Associated species include sphalerite, galena, covellite, cerussite, anglesite, hemimorphite, susannite, bechererite and caledonite (Cooper et al., 2009).
Occurrence in Wales: Cooper et al. (2009) described the new species steverustite based on material from the dumps of Frongoch Mine, near Devil's Bridge in Ceredigion. Somewhat surprisingly - for a new mineral species - the descriptive paper (Cooper et al., 2009) also lists ten other localities where it has been identified. Seven of these are Welsh sites, but it only ever occurs as microcrystals.

Key Localities:

  • Bwlch-glas Mine, Tal-y-bont, Ceredigion: the only in-situ occurrence of steverustite reported by Cooper et al. (2009). 17 samples are known, all collected from a vein exposed in the upper adit level.
  • Esgairhir Mine, Tal-y-bont, Ceredigion: six samples are recorded (Cooper et al., 2009) from the dumps of this prolific supergene mineral producing site.
  • Frongoch Mine, Devil's Bridge, Ceredigion: at this the type locality, steverustite, forms fibrous fan-like bundles of fibrous to acicular crystals in small cavities in quartz veins with other supergene species (Cooper et al., 2009).
  • Hendrefelin Mine, Ysbyty Ystwyth, Ceredigion: Cooper et al. (2009) reported that six samples are known from the dumps of this mine.
  • Llangynog Mine, Llangynog, Powys: rarely found in material on the mine dump. Only two samples are known, one with bechererite in association (Cooper et al., 2009).
  • Llechweddhelyg Mine, Penrhyncoch, Ceredigion: the dumps of this small mine are one of the most productive for steverustite. Cooper et al. (2009) record that 38 samples are known from this site.
  • Nantycar Mine, Rhayader, Powys: according to Cooper et al. (2009), four samples of steverustite are known to have been collected from the dumps at this mine.
  • Penybanc Mine, Tal-y-bont, Ceredigion: Cooper et al. (2009) state that three samples of steverustite have been identified from the dumps of Penybach (sic) Mine, Talybont.

References:

  1. Cooper, M.A., Hawthorne, F.C. and Moffatt, E., 2009. Steverustite, Pb2+5(OH)5[Cu+(S6+O3S2-)3](H2O)2, a new thiosulphate mineral from the Frongoch Mine Dump, Devils Bridge, Ceredigion, Wales. Mineralogical Magazine. 73, 235-250.