Crystal System: Orthorhombic
Status of Occurrence: Unconfirmed Occurrence
Distribution: Locally Abundant
Chemical Composition: Calcium aluminium silicate hydroxide
Chemical Formula: Ca2Al3(SiO4)3OH
Method(s) of Verification: Anglesey - polarizing microscope (Greenly, 1919); Penmaenmawr - polarizing microscope (Sargent, 1925).

Chemical Group:

  • Silicates

Geological Context:

  • Hydrothermal
  • Metamorphic
Introduction: zoisite is member of the epidote group of minerals. It is found most commonly in amphibolite facies metamorphic rocks rich in calcium and is unstable under other conditions. At higher metamorphic grades it may be replaced by calcium-rich plagioclase (Deer et al., 1992).
Occurrence in Wales: two occurrences of zoisite are recorded from Wales, although neither has been substantiated by chemical analysis.

Key Localities:

There are no key localities for this specimen.


  1. Greenly, E., 1919. The Geology of Anglesey. Memoirs of the Geological Survey of Great Britain, 980pp (2 volumes).
  2. Sargent, H.C., 1924. Notes on the petrology of Penmaenmawr Mountain (Part 1). Proceedings of the Liverpool Geological Society, 14, 82-89.