Crystal System: Monoclinic
Status of Occurrence: Confirmed Occurrence
Distribution: Locally Abundant
Chemical Composition: Manganese calcium magnesium oxide hydrate
Chemical Formula: (Mn2+,Ca,Mg)Mn4+3O7.H2O
Method(s) of Verification: not known.

Chemical Group:

  • Oxides & Hydroxides

Geological Context:

  • Supergene: in situ natural oxidation & weathering deposits
Introduction: a secondary manganese mineral produced by weathering or hydrothermal alteration of other manganese-bearing species. Todorokite is the principle manganese oxide in deep-sea manganese nodules.
Occurrence in Wales: todorokite was first reported from Wales by Glasby (1974), who considered it to be the chief alteration product of bedded manganese ore of Cambrian age in the Harlech Dome region of Gwynedd and not pyrolusite, as had been suggested by Woodland (1938c). Allen and Jackson (1985) and Bennett (1987a) also note the presence of todorokite in this area, but probably on the basis of Glasby's original record.

Key Localities:

  • Harlech Dome area, Gwynedd: a weathering product of bedded manganese ore (chiefly rhodochrosite, spessartine and rare rhodonite) within the Hafotty Formation of Cambrian age (Glasby, 1974; Allen and Jackson, 1985).


  1. Allen, P.M. & Jackson, A.A., 1985. Geology of the country around Harlech. Memoirs of the British Geological Survey. Explanation of sheet 135, with part of 149, 112pp.
  2. Bennett, M.A., 1987a. The Cambrian manganese deposits of North Wales. Unpublished Ph.D. thesis, University of Leeds.
  3. Glasby, G.P., 1974. A geochemical study of the manganese ore deposits of the Harlech Dome, North Wales. Journal of Earth Science, 8, 445-450.
  4. Woodland, A.W., 1938c. Some petrological studies in the Harlech Grit Series of Merionethshire. III: The development of pyrite in the grits and mudstones. Geological Magazine, 75, 529-539.