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Cymraeg

Susannite

Crystal System: Trigonal
Status of Occurrence: Confirmed Occurrence
Distribution: Uncommon
Chemical Composition: Lead sulphate carbonate hydroxide
Chemical Formula: Pb4(SO4)(CO3)2(OH)2
Method(s) of Verification: Bwlch-glas Mine - XRD (Rust, 1996); Esgair Hir Mine - XRD (Rust & Mason, 1988); Frongoch Mine - XRD(NMW, X-1155); Llechweddhelyg Mine - XRD (NHM); Nantmelyn Mine - visual; Nant-y-creiau Mine - visual

Geological Context:

Pale yellow pseudohexagonal susannite crystal 0.5 mm across from Frongoch Mine, in the Central Wales Orefield. National Museum of Wales Collection (NMW 2003.1G.M.248), ex J.S. Mason Collection. © National Museum of Wales.
Introduction: susannite is a rare secondary mineral polymorphous with leadhillite and macphersonite. It is found typically as a late stage post-mining phase in lead-bearing mine dumps and in the oxidized portions of lead-bearing orebodies. Susannite is frequently found in association with caledonite.
Occurrence in Wales: generally regarded as rarer than its polymorph leadhillite, susannite is actually the more common species in Wales. Confusion exists over some occurrences as many identifications are referred to as leadhillite or leadhillite-group before further analysis has been carried out. Therefore it is recommended that both the leadhillite and susannite records are consulted. All confirmed records of susannite in Wales are from the Central Wales Orefield, where the vast majority of occurrences are formed by post-mining supergene processes within lead-bearing mine spoil. Typical of post-mining minerals, crystals are small - 2 mm being considered large - but frequently well formed. Rust and Mason (1988) produced the first account of susannite from Wales, at Esgair Hir Mine where, susannite forms groups of rod-like to prismatic crystals within supergene dump-formed mineralization. Subsequent occurrences are noted by Bevins (1994) at other Central Wales minesites including, Llechweddhelyg, Hendrefelen and Frongoch. The discovery at Frongoch soon led to a reputation as the source of the finest Welsh susannite specimens (Green et al., 1996) with crystals reaching 2 mm across. The crystals are not just the largest recorded from Wales, but also the most attractive, frequently displaying stepped growth patterns. Rust (1996) provided an interesting account of the first in-situ susannite, from underground workings at Bwlch-glas mine. Further occurrences of both susannite and leadhillite are listed by Bevins & Mason (1997). However, as no confirmation has been made, most should be regarded as leadhillite-group minerals until further analysis has been made.

Key Localities:

There are no key localities for this specimen.

References:

  1. Bevins, R.E., 1994. A Mineralogy of Wales National Museum of Wales, Geological Series No. 16, Cardiff, 146pp.
  2. Bevins, R.E. & Mason, J.S., 1998. Welsh Metallophyte and metallogenic evaluation project: Results of a Minesite Survey of Gwynedd. National Museums of Wales, Cardiff.
  3. Bevins, R.E. & Mason, J.S., 1997. Welsh metallophyte and metallogenic evaluation project: Results of a minesite survey of Dyfed and Powys. CCW Contract Science Report No. 156. National Museums & Galleries of Wales.
  4. Clark, A.M. & Rust, S.A., 1993. Bottinoite, a mineral new to Britain. Mineralogical Magazine. 57, 543-544.
  5. 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.
  6. Rust, S., 1996. Susannite and caledonite in-situ in Central Wales. U.K. Journal of Mines and Minerals, 17, 18.
  7. Rust, S.A., 1990b. Susannite and sulphatian schmeiderite from Llechwedd Helyg Mine, Tir-y-Mynach, Dyfed, Wales. U.K. Journal of Mines and Minerals, 8, 48
  8. Rust, S.A. & Mason, J.S., 1988. The minerals of Esgair-Hir mine, Dyfed, Wales. UK Journal of Mines & Minerals, 5, 35-43.

There are no references for this specimen.