Mineral Database

Mineral Database
Mineralogy of Wales

Ranciéite

Crystal System: Hexagonal
Formula: (Ca,Mn2+)Mn4+4O9.3H2O
Status of Occurrence: Confirmed Occurrence - 3rd UK recording
Distribution: Rare
Chemical Composition: Hydrated manganese oxide with calcium
Method(s) of Verification: identification of ranciéite is by XRD (no. NMW X-1552) and EDS (Cotterell and Jenkins, 2008).

Stalactitic ranciéite (aggregate 10 cm across) forming on the roof of Dyffryn Adda adit level. D.A. Jenkins photo. © D.A. Jenkins.

Back-scattered electron image of dendritic ranciéite in polished section. National Museum of Wales specimen, no. NMW 2007.35G.M.1a. © National Museum of Wales.

Chemical Group:
  • Oxides & Hydroxides
Geological Context:
  • Supergene : post-mining oxidation & weathering deposits
Introduction: a weathering product of manganese deposits and manganese-bearing minerals, particularly in Ca-rich environments such as limestones. A solid solution series exists between ranciéite and takanelite.
Occurrence in Wales: the only account of ranciéite in Wales was made by Cotterell and Jenkins (2008) who reported the mineral occurring as stalactites in the main drainage adit at Parys Mountain, Anglesey.
Key Localities:
  • Parys Mountain, Anglesey: rancieite occurs as small (< 10 cm) stalactites within the Joint (45 fm.) level at Mynydd Parys as reported by Cotterell and Jenkins (2008).
References:
  • Cotterell, T.F. & Jenkins, D.A., 2008 Ranciéite from Mynydd Parys, Amlwch, Anglesey, Wales.  Journal of the Russell Society, 11, 59-63.