Sulphur

Crystal System: Orthorhombic
Status of Occurrence: Confirmed Occurrence
Distribution: Uncommon
Chemical Composition: Sulphur
Chemical Formula: S
Method(s) of Verification: Dolyhir Quarry - EMPA (Manchester Museum); Frongoch Mine - EMPA (Mancester Museum), all other occurrences visual identification

Geological Context:

  • Supergene: post-mining oxidation & weathering deposits
  • Supergene: in situ natural oxidation & weathering deposits
Pale yellow microcrystals of native sulphur from Llangynog Mine, Powys. Specimen and photo S.A. Rust. © S.A. Rust.
Scanning electron micrograph of a slightly corroded sulphur crystal on altered galena from Llangynog Mine. National Museum of Wales collection (NMW 95.1G.M.3). © National Museum of Wales.
Introduction: native sulphur occurs in three chief geological environments. First and foremost, it is a common mineral in volcanically-active areas, where it is deposited, as a sublimate or as a hydrothermal mineral, near to or at the surface by fumaroles and hot springs. Secondly it is sometimes a major constituent of salt-domes. The third setting, to which all Welsh occurrences belong, is as a mineral formed, most commonly from galena, within the supergene environment. In this context it forms in enclosed, acidic environments and is accompanied by the lead sulphate, anglesite, and sometimes the copper sulphide covellite. Identification of sulphur requires some experience as crystals tend to be small, but the mineral association coupled with the distinctly resinous lustre of the yellowish to greenish-grey crystals is diagnostic.
Occurrence in Wales: old records of sulphur are few. Lentin (1800) and Greenly (1919) reported it from Parys Mountain, Anglesey, while Wedd et al. (1929) described the presence of sulphur in a galena-bearing vein at Nant-y-blaidd Mine in the Llangynog Orefield. More recently, and due to the growing interest in microminerals, sulphur has been noted from a further locality in the Llangynog area, from several localities in the Central Wales Orefield and from three quarries in South and East Wales.

Key Localities:

  • Dan-y-graig Quarry, Risca, Gwent: noted from galena-bearing veins by Alabaster (1983).
  • Dolyhir Quarry, Old Radnor, Powys: microcrystals occur within cavities in part-decomposed intergrown tennantite and galena; associated with anglesite (D.I. Green, unpublished data).
  • Dyfngwm Mine, Penegoes, Powys: on specimens collected by S.A. Rust (listed on Mindat website).
  • Eaglebrook (Nantycagl) Mine, Ceulanymaesmawr, Ceredigion: on specimens collected by S.A. Rust (listed on Mindat website).
  • Frongoch Mine, Devil's Bridge, Ceredigion: occurring as crystals (up to 3 mm) associated with anglesite in part-decomposed galena (Green et al., 1996).
  • Hafan Mine, Ceulanymaesmawr, Ceredigion: on specimens collected by S.A. Rust (listed on Mindat website).
  • Llangynog Mine, Llangynog, Powys: crystals (up to 1.5 mm) associated with anglesite in partly decomposed galena (S.A. Rust collection), also known from a specimen collected by J.S. Mason in 1995.
  • Nant-y-blaidd Mine, Llangynog, Powys: 'in a galena-bearing vein' (Wedd et al., 1929).
  • Ochrwyth Quarry, Risca, Gwent: noted from galena-bearing veins by Alabaster (1983).
  • Parys Mountain, Anglesey: sulphur occurred in the long removed gossan (Lentin, 1800), as yellow veinlets associated with anglesite and a 'yellow-green, earthy lead ore', which Southwood & Bevins (1995) tentatively suggest may have been the pyromorphite described by Greenly (1919).
  • Penrhiw Mine, Ystumtuen, Ceredigion: as blocky crystals (up to 1 mm) with covellite in altered galena (Mason & Green, 1995).

References:

  1. Alabaster, C., 1983. Native sulphur from Stancombe Quarry, Flax Bourton and Dan-y-graig Quarry, Risca (South Wales). Proceedings of the Bristol Naturalists' Society, 43, 13-27.
  2. Green, D.I., Rust, S.A. & Mason, J.S., 1996. Classic British mineral localities: Frongoch Mine, Dyfed. UK Journal of Mines & Minerals, 17, 29-38.
  3. Greenly, E., 1919. The Geology of Anglesey. Memoirs of the Geological Survey of Great Britain, 980pp (2 volumes).
  4. Lentin, A.G.L., 1800. Briefe über die Insel Anglesea, vorzuglich über die dasigen Kupferbergwerke und die dazu gehorigen Schmelzwerke und Fabriken. Leipzig.
  5. Mason, J.S. & Green, D.I., 1995. Supergene minerals including exceptional ramsbeckite from Penrhiw Mine, Ystumtuen, Dyfed. UK Journal of Mines & Minerals, 15, 21-27.
  6. Southwood, M. & Bevins, R.E., 1995. Parys Mountain -The type locality for Anglesite. UK Journal of Mines & Minerals 15, 11-17.
  7. Wedd, C.B., Smith, B., King, W.B.R. & Wray, D.A., 1929. The Country around Oswestry. Memoirs of the Geological Survey of England and Wales. Explanation of Sheet 137.