Crystal System: Monoclinic
Status of Occurrence: Confirmed Occurrence - 1st UK recording
Chemical Composition: Barium hydrate manganese oxide
Chemical Formula: (Ba,H2O)(Mn4+,Mn3+)5O10
Method(s) of Verification: Benallt Mine - XRD (Natural History Museum, specimen B.M. 1944,28, x13062); Tŷ Coch - XRD & EMPA (Criddle & Symes, 1977).
- Supergene: in situ natural oxidation & weathering deposits
Introduction: romanèchite is a secondary mineral, typically a weathering product of manganese-bearing oxides, carbonates or silicates, or within sedimentary deposits.
Occurrence in Wales: a manganese oxide mineral similar in appearance to many others, romanèchite has, only been recorded from two localities in Wales, but is likely to occur at other sites. Many earlier descriptions of manganese minerals simply refer to unidentified manganese oxide minerals as psilomelane and therefore, with further work more occurrences of other manganese minerals may be produced. The occurrence at Tŷ Coch represents the first account of romanèchite from the British Isles.
- Benallt Mine, Llŷn, Gwynedd: identified on a specimen in the Natural History Museum Collection. Romanèchite is likely to form part of the manganese ore, given the abundance of barium phases at Benallt.
- Tŷ Coch, near Porthcawl, South Wales: romanèchite occurs associated with goethite, particularly as vuggy, interlayered masses with cavities lined with fibrous calcite. Romanèchite also forms botryoforms and compound crystallites with goethite (Criddle & Symes, 1977).
- Bevins, R.E., 1994. A Mineralogy of Wales National Museum of Wales, Geological Series No. 16, Cardiff, 146pp.
- Criddle, A.J., & Symes, R.F., 1977. Mineralization at Tŷ Coch, Glamorgan (Mid Glamorgan), Wales: the second occurrence of pyrobelonite. Mineralogical Magazine, 41, 85-90.