Mineral Database

Mineral Database
Mineralogy of Wales

Aeschynite

Crystal System: Orthorhombic
Formula: (Ce,La,Y,Ca,Fe,Th)(Ti,Nb)2(O,OH)6
Status of Occurrence: Confirmed Occurrence - 1st UK recording
Distribution: Rare
Chemical Composition: Rare earth-bearing titanium niobium oxide hydroxide
Method(s) of Verification: backscatter energy dispersive X-ray analysis.

Scanning electron micrograph of aeschynite (white) forming a minute grain in a thin veinlet cutting altered Ordovician intrusive rhyolite from Beddgelert Forest in central Snowdonia. British Geological Survey specimen KB474, © NERC.

Chemical Group:
  • Niobates and Tantalates
Geological Context:
  • Igneous
Introduction: aeschynite is a group name, the individual member species being named on the basis of their rare earth element content, hence aeschynite-(Ce), aeschynite-(Nd) and so on. Aeschynite-(Y) is occasionally found in alkaline pegmatites in association with other rare-earth and niobium bearing minerals.
Occurrence in Wales: A small number of occurrences of aeschynite were noted by the British Geological Survey in Snowdonia during the 1980s and subsequently published by Howells et al. (1991). The material has not been fully characterized though the work done to date suggests that it is highly likely to be aeschynite-(Y).
Key Localities:
  • Snowdonia, Gwynedd: at three localities - Gallt Y Wenallt, Carnedd Y Cribiau and Beddgelert Forest - where altered Ordovician rhyolites outcrop. These carry microscopic veinlets in which small euhedral crystals of aeschynite occur (Howells et al., 1991). Intergrowths with Fe, Mn and Sc-rich Ti and Nb oxides are also present.
References:
  • 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.