It is well illustrated and it is good to see photographs of macrofauna and microflora of the Cambrian rocks of St Tudwal’s Peninsula; thin section photomicrographs, for example the glomeroporphyritic cluster of andesine and augitic clinopyroxene within the Bryn Crin Basaltic Trachyandesite (Plate 18, page 65), are also very welcome.

Abundant phenocrysts and glomerocrysts of altered olivine and fresh clinopyroxene, up to 2 mm across, occur with sporadic microphenocrysts of opaque iron oxide and alkali feldspar (Figure 3.1). The olivine is replaced by carbonate and clay. Euhedral clinopyroxenes are sometimes partially resorbed along their margins and exhibit strong core to rim and sector growth zoning.

The alkali basalts are fine-grained in hand specimen with scattered phenocrysts of greenish olivine up to 5 mm in size. In thin section, the fine-grained groundmass is composed of intergranular olivine, clinopyroxne, plagioclase, Fe–Ti oxides and intersertal glass.

Clinopyroxene

Meaning

Noun

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