Crystal System: Monoclinic
Status of Occurrence: Confirmed Occurrence - 1st UK recording
Distribution: Rare
Chemical Composition: Manganese silicate fluoride hydroxide
Chemical Formula: Mn9(SiO4)4(OH,F)2
Method(s) of Verification: Llŷn Dywarchen - EMPA (Bennett analysis no. 12459 in Bennett, 1987a)

Chemical Group:

  • Silicates

Geological Context:

  • Metamorphic: low-grade
Introduction: sonolite belongs to the humite group of minerals.
Occurrence in Wales: the manganese ore bearing strata in the Harlech Dome area are of Cambrian age and bear a range of manganese minerals. Sonolite forms part of this assemblage, but has only been identified by electron microprobe analysis.

Key Localities:

  • Llŷn Dywarchen, Moel Ysgyfarnogod, Gwynedd: Bennett (1987a) reported the presence of rare orange-yellow Mn-humite associated with barite in a micro-concretion and also in adjacent carbonate-rich red laminated ore in the manganese ore bed of the Hafotty Formation (e.g. National Museum of Wales specimen NMW 24.479.GR32).


  1. Bennett, M.A., 1987a. The Cambrian manganese deposits of North Wales. Unpublished Ph.D. thesis, University of Leeds.