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Slightly deformed prismatic clinzoisite within calcite-quartz vein cutting metabasite. Gellilydan, Ffestiniog. Specimen National Museum of Wales (NMW 2005.3G.M.2), photo D.I. Green, © National Musuem of Wales.
a member of the epidote group, clinozoisite and epidote (with which it forms a solid solution) can be difficult to distinguish without employing analytical methods. Clinozoisite typically occurs in basic igneous rocks that have undergone low and medium-grade (greenschist and amphibolite facies) metamorphism. It also occurs in alpine fissure-type veins cutting low-grade metamorphic rocks. In such associations, coarsely-crystalline clinozoisite is typically a brownish or buff colour, in contrast to the distinctive, bright pistachio-green of epidote.
many early descriptions of altered basic igneous rocks from Wales refer to the presence of epidote: however, Roberts (1981) reported the widespread presence of clinozoisite in rocks from Central Snowdonia and Llŷn. Similarly, many so-called epidotes from the Mynydd Preseli region of SW Wales are clinozoisite (R.E. Bevins, unpublished data). More recently, the presence of locally abundant and coarse-grained clinozoisite in 'alpine fissure-type' veins has been noted from a number of sites within the Dolgellau Gold-belt.