Ireland - phyllite ECOS, Frome, Somerset
European Community Of Stone

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Metamorphic block

Signs of cleavage

About the rock: In the far south west of Ireland, beneath a thick cover of Old Red Sandstone, there are equally thick outcrops of Silurian greywacke and mudstones in a facies comparable with the rocks which we see in Cardiganshire. In both areas, we are seeing rocks which were deposited by turbidity currents in deep elongate basins. In both areas too, they are rocks which have been mildly changed by pressure during folding to assume a cleavage. Some of the surfaces of this irregularly shaped block are cleavage planes. Some areas are decidedly flinty, possibly giving rise to the suggestion that this is ‘quartzite’. Overall, however, it does not look like metamorphosed sandstone. It is fine-grained with a dictinct green colour. The cleavage planes are not as perfectly formed as they would be in slate but the monerals are not large enough, nor is sufficient mica in evidence for the rock to be called a schist. It is suggested that this rock is phyllite, the mineral chlorite giving the green colour. It was metamorphosed from an original mudstone. Place of origin: This block came from one of the ‘superquarries’ on the shores of Bantry Bay, County Cork, a deep fjord-like inlet. The rock is loaded directly from the quarry on to huge ships and is used as a mass aggregate material.