OU-4 Penmaenmawr microdiorite
Purchase Code: QC-8
IAG members: £ 65
Non-Members: £ 100
This microgranite was collected from Graig Llwyd Quarry, Penmaenmawr, North Wales. The igneous body which comprises the Penmaenmawr microdiorite is a minor instruction, oval in shape and 3 x 1.5 km2 in size. It is thought to be part of the Ordovician-age Llewelyn volcanic group, located near Conway on the North Wales coast. The rock is fine grained with an average crystal size of 0.2mm, consisting of plagioclase feldspar, chlorite, clinopyroxene and quartz. A small number of phenocrysts, mainly plagioclase, range up to 2 mm in length, Although this rock was originally chilled rapidly, the igneous mineralogy has been partly over-printed as a result of low-grade greenschist facies metamorphism.
The material is available in units of 35 g packaged in a polyethylene sachet.