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white vesicles containing phillipsite-(Ca) and minor mesolite or scolecite have been identified (T.F. Cotterell, unpublished data) in a specimen of Tertiary age olivine-dolerite labelled as from a dyke cutting the Bwlch-y-Gywion granite at Nant Ffrancon.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 key localities for this specimen.


There are no references for this specimen.