Grovesite, syn. of pennantite

Crystal System: Monoclinic
Status of Occurrence: Confirmed Occurrence - Type Locality In Wales
Distribution: Rare
Chemical Composition: manganese magnesium aluminium silicate hydroxide
Chemical Formula: (Mn,Mg,Al)3(Si,Al)2(O,OH)9
Method(s) of Verification: grovesite was originally characterized on the basis of X-ray powder and rotation photographs and chemical analysis (Bannister et al., 1955).

Chemical Group:

  • Silicates

Geological Context:

  • Metamorphic: low-grade
Introduction: a synonym of pennantite-Ia. Grovesite was described as a new species by Bannister et al. (1955), but later shown by Peacor et al. (1974) to be similar to pennantite. Bayliss (1983) showed there to be two polytypes of pennantite, pennantite-Ia being the mineral previously called grovesite. Thus the name grovesite has been relegated to synonym status.
Occurrence in Wales: Bannister et al. (1955) described grovesite as a new mineral from the No. 5 ore-body at Benallt Mine, on Llŷn. Grovesite was named in honour of Dr. A. W. Groves, of the Mineral Resources Division of the Colonial Geological Surveys, who was geologist to the Home Ore Department, Iron and Steel Control, Ministry of Supply, during the Second World War. Dr. Groves produced a detailed report on the geology and mineralogy of the Benallt and Nant manganese mines (in Groves, 1952) and kept watch for unusual minerals at these mines, which he reported to the British Museum (now the Natural History Museum, London). As noted in the introduction this mineral has been shown to be a type of pennantite. Further details can been found in the pennantite entry.

Key Localities:

There are no key localities for this specimen.


  1. Bannister, F.A., Hey, M.H. and Campbell Smith, W., 1955. Grovesite, the manganese-rich analogue of berthierine. Mineralogical Magazine, 30, 645-647.
  2. Bayliss, P., 1983. The polytypes of pennantite. Canadian Mineralogist, 21(3), 545-547.
  3. Groves, A.W., 1952. Wartime investigation into the hematite and manganese ore resources of Great Britain and Northern Ireland. Ministry of Supply, Permanent Records of Research and Development. Monograph No. 20-703.
  4. Peacor, D.R., Essene, E.J., Simmons, W.B. and Bigelow, W.C., 1974. Kellyite, a new Mn-Al member of the serpentine group from Bald Knob, North Carolina, and new data on grovesite. American Mineralogist, 59, 1153-1156.