Crystal System: Triclinic
Status of Occurrence: Confirmed Occurrence
Chemical Composition: Zinc iron manganese oxide hydrate
Chemical Formula: (Zn,Fe2+)Mn4+3O7.3H2O
Method(s) of Verification: Drosgol Mine - XRD & EMPA (National Museum of Wales, NMW X-1281).
- Oxides & Hydroxides
Chalcophanite rosette in manganese ore from Drosgol Mine, Ponterwyd, Ceredigion. Photo T.F. Cotterell, © National Museum of Wales.
Scanning electron micrograph of rosetted aggregates of platy chalcophanite crystals from Drosgol Mine. Scale bar 1 mm. Image T.F. Cotterell, © National Museum of Wales.
Chalcophanite-bearing manganese ore from Drosgol Mine, Central Wales Orefield. J.S. Mason Collection (JMDL 503). Photo D.I. Green, © D.I. Green.
Introduction: chalcophanite is a secondary manganese mineral formed through supergene (near surface) alteration of zinc- and manganese-bearing base-metal deposits. It is usually associated with other Mn-dominated oxide minerals.
Occurrence in Wales: the only previous record of chalcophanite from the UK was as a minor component of supergene manganiferous ironstone near Tomintoul, Banffshire, Scotland (Nicholson, 1989). The occurrence of significant quantities of chalcophanite from old manganese trials on the hill of Drosgol in Central Wales (Cotterell & Mason, 2003) is noteworthy. The true nature of this supergene manganese oxide mineralization, noted by Jones (1922) as 'psilomelane', was only revealed relatively recently, during research into material collected during the 1996 phase of the MINESCAN project (Bevins & Mason, 1997).
- Drosgol Mine, Drosgol, Ponterwyd, Ceredigion: chalcophanite occurs as a major component of a dark grey manganese oxide assemblage cementing brecciated highly bleached mudstone. It forms metallic, bluish grey massive aggregates and also platy, micaceous crystals lining open cavities within the oxide-dominated matrix (Cotterell & Mason, 2003).
- 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.
- Cotterell, T.F., & Mason, J.S., 2003. Chalcophanite from Drosgol Mine, Ponterwyd, Ceredigion: The First Welsh Occurrence. UK Journal of Mines and Minerals, 23, 39-40.
- Jones, O.T., 1922. Lead and zinc. The mining district of North Cardiganshire and West Montgomeryshire. Memoirs of the Geological Survey. Special Report of the Mineral Resources of Great Britain, 20.
- Nicholson, K., 1989. Manganese oxides from the British Isles. Mineralogical Magazine, 53, 637-638.