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Crystal System: Tetragonal
Status of Occurrence: Confirmed Occurrence
Distribution: Locally Abundant
Chemical Composition: Manganese oxide
Chemical Formula: MnO2
Method(s) of Verification: Benallt Mine - XRD (Natural History Museum, x4271); Tŷ Coch - XRD (Natural History Museum, x18701); Snowbrook Mine - XRD (NMW X-1293); Mynydd Nodol - XRD (NMW X-1477); Nant Uchaf Mine - XRD (NMW X-1503).

Chemical Group:

Geological Context:

Acicular pyrolusite in stalactitic growths coated with rusty 'limonite' and with a core of massive black cryptomelane. Nant Uchaf Mine. National Museum of Wales Collection (NMW 83.41G.M.3757). Photo D.I. Green, © National Museum of Wales.
Introduction: a manganese oxide belonging to the rutile group of minerals, it is trimorphous (has the same composition but a different atomic strucure) with akhtenskite and ramsdellite. Pyrolusite is a secondary mineral which forms by alteration of manganese ore minerals.
Occurrence in Wales: pyrolusite is probably widespread in Wales, although there are few specific records of its occurrence. Bevins (1994) reported pyrolusite from Benallt Mine, on Llŷn and from Tŷ Coch, in South Wales on the basis of X-ray diffraction analyses at the Natural History Museum, London. Research into the characterization of manganese species from across Wales has produced four further localities (T.F. Cotterell, unpublished data).

Key Localities:


  1. Bevins, R.E., 1994. A Mineralogy of Wales National Museum of Wales, Geological Series No. 16, Cardiff, 146pp.