Introduction:

a manganese-rich chlorite group mineral typically formed during hydrothermal alteration of manganese deposits. Pennantite was first discovered in manganese ores at Benallt Mine, Llŷn, Gwynedd, North Wales and is named in honour of the Welsh mineralogist Thomas Pennant (1726-1798). Two polytypes are known, pennantite-IIb and pennantite-Ia, of which IIb represents the original material described by Campbell Smith at al. (1946) and Ia the mineral grovesite, described as a new species by Bannister et al. in 1955, but shown by Bayliss (1983) to be a polytype of pennantite.

Occurrence in Wales:

the new mineral pennantite was first described by Campbell Smith et al. (1946) from specimens collected from the Ty Canol incline at Benallt Mine, Rhiw, Llŷn. Type material is held at the Natural History Museum, London, registered as B.M. 1947, 295. The mineral described by Bannister et al. (1955) as grovesite, but now regarded as pennantite-Ia was discovered in the No. 5 ore-body at Benallt Mine. More recently Bennett (1987b) has reported the occurrence of pennantite in the manganese ore bed of the Hafotty Formation of Cambrian age, exposed in the Harlech Dome area of Gwynedd.

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