Mineral Database (Saesneg yn unig)

Mineral Database (Saesneg yn unig)
Mineralogy of Wales

Braunite

Crystal System: Tetragonal
Formula: Mn2+Mn3+6SiO12
Status of Occurrence: Confirmed Occurrence - 1st UK recording
Distribution: Rare
Chemical Composition: Manganese silicate
Method(s) of Verification: Nant Mine - XRD at the Natural History Museum, London (X-ray numbers x17911 & x18399).
Geological Context:
  • Hydrothermal
  • Hydrothermal : limestone hosted hematite deposits
Introduction:

braunite is a brownish black mineral that forms a series with abswurmbachite, (Cu,Mn2+)Mn3+6SiO12. It is formed by metamorphism of manganese silicates and oxides and may also be produced as a weathering product.

Occurrence in Wales:

two occurrences of braunite are known from Wales. Criddle & Symes (1977) reported the first UK occurrence of braunite from the manganese deposit at Ty-coch in South Wales. Braunite has subsequently been confirmed from specimens from Nant Mine, LlÅ·n collected, but not analysed, prior to the work of Criddle & Symes (1977).

Key Localities:
  • Nant Mine, Nant-y-Gadwen, Rhiw, Llŷn, Gwynedd: The Natural History Museum, London holds specimens from the Russell Collection from which the presence of braunite has been confirmed by X-ray analysis. No further data is available currently.
  • Ty-coch, near Porthcawl, South Wales: braunite occurs in manganese ore from a disused mine at this locality. It forms euhedral to subhedral grains associated with hausmannite, interstitial and vug-filling calcite, manganocalcite, ferroan calcite, dolomite, barite and rarer pyrobelonite and vanadinite (Criddle & Symes, 1977).
References:
  • Criddle, A.J., & Symes, R.F., 1977 Mineralization at Ty-coch, Glamorgan (Mid Glamorgan), Wales: the second occurrence of pyrobelonite. 

    Mineralogical Magazine, 41, 85-90.