Wollastonite

Crystal System: Triclinic
Status of Occurrence: Confirmed Occurrence
Distribution: Rare
Chemical Composition: Calcium silicate
Chemical Formula: CaSiO3
Method(s) of Verification: Plas Newydd - EMPA (NMW unpublished data)

Chemical Group:

  • Silicates

Geological Context:

  • Metamorphic: skarn mineralization
Introduction: wollastonite forms by contact metamorphism of impure limestone and in skarns where silica is introduced into limestones. It is associated typically with calcite and other calc-silicate minerals such as diopside, grossular, and vesuvianite.
Occurrence in Wales: wollastonite is known from just one locality in Wales, from the contact zone between the Plas Newydd dyke and impure Carboniferous Limestone. Although smaller dykes cut limestone elsewhere on Anglesey, the considerable width of the Plas Newydd dyke provided sufficient heat to metamorphose the limestone into which it intruded around 60 million years ago.

Key Localities:

  • Plas Newydd, Anglesey: wollastonite occurs within the contact zone between limestone and the Plas Newydd dyke. It forms radiating sprays of needle-like crystals, up to 0.5 mm long, associated with vesuvianite and calcite. A lack of quartz suggests that either this mineral was consumed during the wollastonite forming reaction or more likely that wollastonite formation was controlled by introduced of silica into the contact zone.

References:

There are no references for this specimen.