Crystal System: Monoclinic
Status of Occurrence: Confirmed Occurrence - 3rd UK recording
Chemical Composition: barium aluminium phosphate hydroxide
Chemical Formula: BaAl3(PO4)(PO3OH)(OH)6
Method(s) of Verification: XRD (no. NMW X-2222) and EDS at the National Museum of Wales.
- Supergene: post-mining oxidation & weathering deposits
Scanning electron micrograph of gorceixite rosettes from Benallt mine. National Museum of Wales specimen no. NMW 2009.60G.M.2 b. © National Museum of Wales.
Scanning electron micrograph of a gorceixite rosette from Benallt mine. National Museum of Wales specimen no. NMW 2009.60G.M.2 b. © National Museum of Wales.
Introduction: gorceixite is a member of the alunite supergroup known to occur in a diverse range of geological environments. Worldwide it has been confirmed in igneous, sedimentary and metamorphic rocks.
Occurrence in Wales: this unusual British mineral has recently (2009) been identified at Benallt mine, where it forms pearly white coatings consisting of aggregates of minute platy crystals. The more crystalline specimens reveal rosette-like aggregates of platy crystals, but each rosette rarely exceeds 0.2 mm in diameter.
- Benallt Mine, Llŷn, Gwynedd: gorceixite has been identified as coatings on banalsite- and apatite-(F)-bearing matrix from the dumps of this mine. It is unclear when exactly this mineral formed, but it is probably post-mining in origin, forming within the mine dump (Cotterell and Tayler, in press).
- Cotterell, T.F. and Tayler, R., in press. Gorceixite from Benallt manganese mine, Rhiw, Pen Llŷn, Gwynedd, Wales. UK Journal of Mines and Minerals.