Crystal System: Monoclinic
Status of Occurrence: Confirmed Occurrence
Distribution: Rare
Chemical Composition: Hydrated calcium-dominant aluminosilicate
Chemical Formula: Ca3(Si10Al6)O32.12H2O
Method(s) of Verification: XRD (numbers NMW X-2324 and X-2325) and EDS at the National Museum of Wales. EDS shows that Ca is slightly dominant over K.

Chemical Group:

  • Silicates

Geological Context:

  • Igneous
  • Hydrothermal: amygdale infill & veins in volcanic rocks
Introduction: phillipsite-(Ca) is the calcium-dominant member of the phillipsite series of zeolites. It typically occurs in cavities (vesicles) in basalts and dolerites.
Occurrence in Wales: a specimen of olivine-dolerite derived from a Tertiary dyke cutting through the Ordovician Bwlch-y-Gywion granite at Nant Ffrancon, Gwynedd, contains white vesicles containing dominant phillipsite-(Ca).

Key Localities:

  • Nant Ffrancon, Gwynedd: white vesicles containing phillipsite-(Ca) and minor mesolite or scolecite have been identified (T.F. Cotterell, unpublished data) in a specimen of Tertiary age olivine-dolerite labelled as from a dyke cutting the Bwlch-y-Gywion granite at Nant Ffrancon. The specimen is number NMW 78.20G.R.439 in the collections at the National Museum of Wales.


There are no references for this specimen.