Crystal System: Orthorhombic
Status of Occurrence: Unconfirmed Occurrence
Distribution: Rare
Chemical Composition: Manganese silicate hydroxide
Chemical Formula: Mn8Si6O15(OH)10
Method(s) of Verification: none known.

Chemical Group:

  • Oxides & Hydroxides
Introduction: bementite is a rare manganese mineral that is found in manganese ore deposits and may be associated with typical manganese ore minerals such as hausmannite, jacobsite, braunite and alleghanyite.
Occurrence in Wales: Bevins (1994) recorded that specimen B.M. 1964, R10624, in the Natural History Museum, London is bementite from Nant Mine, Llŷn. No details are known regarding the method of identification. Recent research into the mineralogy of the Benallt and Nant manganese mines suggests that this is probably a mis-identification of caryopilite (T.F. Cotterell, unpublished data). Particularly given the fact that Kato (1963) considered that much material described as bementite is actually caryopilite and that caryopilite has recently been confirmed from Nant Mine by both XRD and EMPA (Cotterell, 2006).

Key Localities:

  • Nant Mine, Nant-y-Gadwen, Rhiw, Llŷn, Gwynedd: The Natural History Museum collections contain a specimen labelled as bementite (B.M. 1964, R10624). No further details of this specimen or occurrence are known, but it is suspected that this is actually the similar looking species, caryopilite (T.F. Cotterell, unpublished data).


  1. Bevins, R.E., 1994. A Mineralogy of Wales National Museum of Wales, Geological Series No. 16, Cardiff, 146pp.
  2. Cotterell, T.F., 2006. Caryopilite and pyroxmangite from Nant Mine, Nant-y-Gadwen, Llanfaelrhys, Pen Llyn, Gwynedd, Wales UK Journal of Mines and Minerals, 27, 51-53.
  3. Kato, T., 1963.. J. Min. Soc. Japan, 6, 93.