Mineral Database

Mineral Database
Mineralogy of Wales

Feitknechtite

Crystal System: Hexagonal
Formula: ß-MnO(OH)
Status of Occurrence: Confirmed Occurrence - 1st UK recording
Distribution: Rare
Chemical Composition: Manganese oxide hydroxide
Method(s) of Verification: Benallt manganese mine: XRD at the National Museum of Wales (XRD no. NMW X-1867).

Coarse brown bladed aggregates of intergrown hausmannite and feitknechtite from Benallt mine. Specimen is 11 cm across. National Museum of Wales specimen, no. NMW 58.444.GR.2. © National Museum of Wales.

Chemical Group:
  • Oxides & Hydroxides
Geological Context:
  • Supergene
Introduction:

a rare manganese oxide hydroxide, trimorphous with manganite and groutite. Feitknechtite typically forms intergrown with hausmannite in a mixture that was previously called hydrohausmannite (Frondel, 1953). Bricker (1965) demonstrated that hydrohausmannite was in fact a mixture of of two phases: hausmannite and the new mineral feiknechtite.

Occurrence in Wales:

feitknechtite has been discovered (Cotterell, 2008) as a component of bladed manganese ore from Benallt Mine at the southern end of Pen Llŷn in Gwynedd. This occurrence matches descriptions of feitknechtite from Franklin, New Jersey, U.S.A., and Långban and Pajsberg, Värmland, Sweden.

Key Localities:
  • Benallt Mine, Llŷn, Gwyneddŷ: coarse brown bladed crystals in ore from Benallt manganese mine consist of an intimate mixture of hausmannite and feitknechtite typical of what was once termed 'hydrohausmannite'. This ore is believed to have originally consisted of pyrochroite which altered on exposure to air. A full description is provided by Cotterell (2008).
References:
  • Bricker, O., 1965 Some stability relations in the system Mn-O2-H2O at 25° and one atmosphere total pressure.  American Mineralogist, 50, 1296-1354.
  • Cotterell, T.F., 2008 The first British occurrence of feitknechtite at Benallt manganese mine, Rhiw, Pen Llŷn, Gwynedd, Wales. 

    UK Journal of Mines and Minerals, 29, 47-48.

  • Frondel, C., 1953 New manganese oxides: hydrohausmannite and woodruffite.  American Mineralogist, 38, 761-769.