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Crystal System: Trigonal
Status of Occurrence: Confirmed Occurrence
Distribution: Locally Abundant
Chemical Composition: Zinc carbonate
Chemical Formula: ZnCO3
Method(s) of Verification: Cwmystwyth Mine - XRD (NMW X-1291); Dolyhir Quarry - EMPA (Mike Rothwell); Llantrisant -XRD (NMW X-824); Machen Quarry - XRD (NMW X-960); Ochr-Chwith - XRD (NHM, x14629); Rhosesmor Mine - XRD (NMW, REB 37); Rhyd-y-Gwern Mine – XRD (NHM, x15836).

Chemical Group:

Geological Context:

Botryoidal smithsonite. Halkyn Mountain, Flintshire. National Museum of Wales Collection (85.70G.M.35). Photo M.P. Cooper, © National Museum of Wales.
Introduction: smithsonite is a secondary zinc carbonate typically found in the oxidized zone of zinc-bearing ore bodies or as a replacement of adjacent calcareous rocks. Smithsonite is frequently confused with the similar looking zinc silicate, hemimorphite, both of which were at one time known by the name calamine. When well crystallized identification is straightforward to the trained eye, however, both can form botryoidal masses of similar colours. Associated species include hemimorphite, cerussite, malachite, azurite, anglesite, pyromorphite, aurichalcite, and hydrozincite.
Occurrence in Wales: smithsonite is one of the earliest minerals to have been reported in Wales. Smithsonite has long been known to occur in Flintshire. Thomas Pennant (1726-1798) kept a catalogue of mineral specimens collected from the mines of Flintshire within which forty-five specimens are described (Campbell Smith, 1913). Indeed the first analysis of smithsonite appears to have been on material from “Holywell, Anglia” (Bergmann, 1780), clearly the well-known locality in Flintshire (Clark, 1993). Flintshire, and in particular the Halkyn District remain the most important region in Wales for smithsonite, although a number of other minor discoveries have been made across Wales. In Central Wales smithsonite occurs at a limited number of localities, although it has been reported from many more. Many of the sites described by Jones & Moreton (1977) have been shown to be hemimorphite (T.F. Cotterell, unpublished data). Smithsonite has however, been confirmed from Cwmystwyth Mine, but only as thin coatings on sphalerite, and never as crystals (T.F. Cotterell, unpublished data). In South Wales smithsonite is known from oxidized veins cutting the southern outcrop of Carboniferous Limestone. Notable localities include Machen Quarry and the Clive mines both near Caerphilly, but specimens are always small.

Key Localities:


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