Mineral Database

Mineral Database
Mineralogy of Wales

Synchysite-(Y)

Crystal System: Orthorhombic
Formula: Ca(Y,Ce,La,Nd)(CO3)2F
Status of Occurrence: Confirmed Occurrence - 1st UK recording
Distribution: Rare
Chemical Composition: Calcium rare earth fluorocarbonate
Method(s) of Verification: Beddgelert Forest - SEM EDX (Kearsley, Natural History Museum, unpublished data)
Chemical Group:
  • Carbonates
Geological Context:
  • Hydrothermal
  • Igneous
Introduction: synchysite-(Y) is limited in its occurrence to a relatively small number of paragenetic situations. It occurs in pegmatites, in carbonatites and in alpine fissure-type veins, where it is typically accompanied by other rare-earth element-bearing minerals and quartz, albite, the TiO2 polymorphs and chlorite.
Occurrence in Wales: the only record of synchysite-(Y) from Wales was cited by Bevins (1994), based on unpublished data provided by A.T. Kearsley. The occurrence, identified by energy-dispersive x-ray analysis, was in altered rhyolite in the Beddgelert district of Snowdonia. All other synchysites from Wales have been shown, by analyses, to be synchysite-(Ce) with only a minor yttrium content.
Key Localities:
  • Beddgelert Forest, Beddgelert, Gwynedd: radiating sheaves intergrown with quartz and K-feldspar in altered rhyolite (Bevins, 1994). No other details of this occurrence are known: however undifferentiated synchysite from rhyolite in Snowdonia, in similar habits and associations, is illustrated by Howells et al. (1991).
References:
  • Bevins, R.E., 1994 A Mineralogy of Wales  National Museum of Wales, Geological Series No. 16, Cardiff, 146pp.
  • Howells, M.F., Reedman, A.J. & Campbell, S.D.G., 1991 Ordovician (Caradoc) marginal basin volcanism in Snowdonia (north-west Wales).  HMSO for the British Geological Survey, 191pp.