Crystal System: Orthorhombic
Status of Occurrence: Confirmed Occurrence - 1st UK recording
Distribution: Rare
Chemical Composition: Manganese magnesium silicate hydroxide
Chemical Formula: (Mn,Mg)7(SiO4)3(OH)2
Method(s) of Verification: Harlech Dome - EMPA (Bennett, 1987a, analysis 12457).

Chemical Group:

  • Silicates

Geological Context:

  • Metamorphic: skarn mineralization
  • Metamorphic: low-grade
Introduction: a rare manganese magnesium silicate mineral belonging to the humite group. It is typically found in manganese deposits metamorphosed under amphibolite facies conditions and as a late-stage skarn mineral (Anthony et al., 1995).
Occurrence in Wales: Bennett (1987a) reported manganhumite from the Cambrian manganese deposits of the Harlech Dome area of Gwynedd. This appears to be the first recording of this mineral in the British Isles.

Key Localities:

  • Llŷn Dywarchen, Moel Ysgyfarnogod, Gwynedd: Bennett (1987a) reported the presence of rare, orange-yellow Mn-humite associated with barite in a microconcretion and in adjacent carbonate-rich, red laminated ore in the manganese ore bed of the Hafotty Formation of Cambrian age from Llŷn Dywarchen near Moel Ysgyfarnogod.


  1. Anthony J., Bideaux R., Bladh K. & Nichols M., 1995. Handbook of Mineralogy, vol. 2 (parts 2/1 and 2/2), Silica, Silicates
  2. Bennett, M.A., 1987a. The Cambrian manganese deposits of North Wales. Unpublished Ph.D. thesis, University of Leeds.