Crystal System: Monoclinic
Status of Occurrence: Discredited Occurrence
Distribution: None - Discredited
Chemical Composition: Iron antimony sulphide
Chemical Formula: FeSbS
Method(s) of Verification: Esgairhir Mine - original identifcation visual, subsequently discredited by XRD/EMPA (Mason, 1998).

Chemical Group:

  • Sulphides

Geological Context:

  • Hydrothermal: epithermal polymetallic veins & pipes
Tucekite (crystal, 0.5 mm long) in polished section from Henfwlch Mine, Central Wales. Tucekite from Esgairhir Mine was previously identified as gudmundite. J.S. Mason specimen. © J.S. Mason.
Introduction: gudmundite can occur in a wide variety of hydrothermal ore deposits in association with other sulpharsenides and sulphantimonides, but is usually only an accessory or minor member of any given assemblage.
Occurrence in Wales: in 1988, Rust & Mason reported, in describing the primary mineral paragenesis at Esgairhir Mine in Central Wales, the presence of laths and prismatic crystals of a mineral with the optical properties of gudmundite, overgrowing 'linnaeite' and millerite. Subsequent analytical work, however, correctly identified this mineral to be tucekite (Mason, 1998): therefore gudmundite and references to it at Esgairhir Mine should be amended appropriately.

Key Localities:

There are no key localities for this specimen.


  1. Mason, J.S., 1998. Tucekite, a mineral new to Britain, and other rare ore minerals from the Central Wales Orefield. UK Journal of Mines and Minerals, 19, 30-36.
  2. Rust, S.A. & Mason, J.S., 1988. The minerals of Esgair-Hir mine, Dyfed, Wales. UK Journal of Mines & Minerals, 5, 35-43.