Crystal System: Monoclinic
Status of Occurrence: Confirmed Occurrence - 1st UK recording
Distribution: Rare
Chemical Composition: Calcium potassium barium sodium manganese aluminium silicate hydroxide hydrate
Chemical Formula: (Ca,K,Ba,Na)3-4Mn24(Si,Al)40(O,OH)112.21H2O
Method(s) of Verification: Benallt Mine - XRD & EMPA (National Museum of Wales & Open University).

Chemical Group:

  • Silicates

Geological Context:

  • Metamorphic: low-grade
Introduction: tamaite is the recently described (Matsubara et al., 2000) Ca-analogue of ganophyllite which forms in veinlets within metamorphosed manganese ore, probably during low-grade metamorphism.
Occurrence in Wales: in the paper describing tamaite as a new mineral species Matsubara et al. (2000) note that Ca-dominant ganophyllite was recorded by Haga (in Kato, 1980) from Benallt Mine, Carnavonshire (sic), England (sic). Recent microprobe analyses on material collected from the dumps at Benallt Mine has also produced compositions consistent with tamaite (T.F. Cotterell/A. Tindle, unpublished data).

Key Localities:

There are no key localities for this specimen.


  1. Kato, T., 1980. The crystal structure of ganophyllite; monoclinic subcell. Mineralogical Journal. 10, 1-13.
  2. Matsubara, S., Miyawaki, R., Tiba, T. & Imai, H., 2000. Tamaite, the Ca-analogue of ganophyllite, from the Shiromaru mine, Okutama, Tokyo, Japan. Journal of Mineralogical and Petrological Sciences. 95, 79-83.