Crystal System: Monoclinic
Status of Occurrence: Confirmed Occurrence - 1st UK recording
Distribution: Rare
Chemical Composition: Calcium strontium aluminium iron silicate hydroxide
Chemical Formula: CaSrAl2Fe3+(Si2O7)(SiO4)O(OH)
Method(s) of Verification: Benallt Mine - XRD and EDS at the National Museum of Wales (XRD no. NMW X-1756) and EPMA at the Open University, Milton Keynes.

Chemical Group:

  • Silicates

Geological Context:

  • Metamorphic: low-grade
Introduction: a rare member of the epidote group discovered within low temperature metamorphosed manganese-iron ore deposits.
Occurrence in Wales: this unusual mineral has been identified in dump material at Benallt Mine (Cotterell and Tayler, in press).

Key Localities:

  • Benallt Mine, Llŷn, Gwynedd: small crimson red needles found associated with pyrophanite in crystallized celsian on the dumps are almost exclusively epidote-(Sr) with just one grain shown to be piemontite-(Sr) (Cotterell and Tayler, in press).


  1. Cotterell, T.F. and Tayler, R., in press. Epidote-(Sr) and piemontite-(Sr), two minerals new to the British Isles from Benallt manganese mine, Rhiw, Pen Llŷn, Gwynedd, Wales. UK Journal of Mines and Minerals.