Wales has a rich history of manganese mining. Bedded manganese ores in the Harlech Dome were worked on a small scale during the latter part of the 19th century, but proved too low-grade to be economic. The deposits are, however, extensive and may one day be of use. Higher-grade manganiferous metamorphosed oolitic mudstones at Rhiw on Llŷn hosted the largest manganese mines in the British Isles during the early and middle of the 20th century. Other, less significant deposits include vein hosted manganese oxides within volcanic ash-flows in the Arennig area and other parts of Gwynedd, while near-surface supergene manganese deposits occur within the Central Wales Orefield.
Manganese minerals are traditionally poorly understood, owing to a reputation of being dull looking, black and poorly crystallized. Consequently historical identifications and characterizations are often incorrect and significant potential exists for new discoveries to be made. A comprehensive, systematic review of manganese mineralization in Wales using X-ray diffraction (XRD) and scanning electron microscopy — energy dispersive spectroscopy (SEM-EDS) analyses is being carried out. Many unusual manganese-bearing mineral species not previously recorded in Wales, or indeed the British Isles have been identified.