Ardilistry Bay, Islay
Geological Conservation Review site | GCR #3290 | Structural and Metamorphic Geology | Dalradian
Geological Conservation Review site | GCR #3290 | Structural and Metamorphic Geology | Dalradian
Scotland's geosites are chosen because of their local, national or international importance. Take only photos, leave only footprints: avoid causing any damage to this site. You can walk almost anywhere in Scotland without the need to ask permission or keep to paths, but you have a responsibility to care for your own safety, to respect people's privacy and peace of mind and to cause no damage.
The right of access does not extend to quarries, building sites or any land where public access is prohibited, or to the collection of geological samples.
Along the coast of Islay to the east of Port Ellen metamorphosed sills account for up to half of the succession. One of the sills, exposed along the shoreline of Ardilistry Bay, is quite rare in the British Isles.
Metapyroxenite rocks are relatively rare in the British Isles. They are found in the Lewisian Gneiss Complex of north-west Scotland, which are generally at a high metamorphic grade (amphibolite- to granulite-facies), and occur as very low-grade rocks, such as in the Unst and the Ballantrae Ophiolite-complexes. However, it is possible that the metapyroxenite at Ardilistry Bay may be the only greenschist-facies metapyroxenite preserved and exposed in the British Isles.
The metapyroxenite layer is up to 3 m thick and consists almost entirely of coarse-grained actinolite, a Mg-rich calcic amphibole that has replaced original clinopyroxene during metamorphism. It occurs in a sill that also has a 1 m-thick layer of meta-anorthosite, representing an original plagioclase-rich layer. The sill, therefore, is an excellent example of a layered basic igneous intrusion that has been metamorphosed to the greenschist facies. Whereas, deformation and fluids associated with the metamorphism have altered the margins of the sill, which now has a schistose fabric, the inner part has retained the original igneous textures, particularly in the metapyroxenite and meta-anorthosite layers. The good exposure, and the very distinctive appearance of this rock, enhances the geological attractiveness of an already geologically fascinating small corner of Islay.
Excursion 11 in 'A guide to the Geology of Islay' 2025 Edition
Excursion loaded as pdf in photograph section
Link to Geology of Islay website
pdf of GCR site description extracted from Tanner, P.G., Bendall, C.A., Pickett, E.A., Roberts, J.L., Treagus, J.E. and Stephenson, D. 2013. The Dalradian rocks of the south-west Grampian Highlands of Scotland. Proceedings of the Geologists' Association, 124, 83-147.
https://sitelink.nature.scot/site/76
Link to Ardmore, Kildalton and Callumkill Woodlands SSSI. The GCR site is included within this much larger woodland SSSI
David Webster
(PDF) Excursion 11 from 'A Guide to the Geology of Islay' 2025 Edition
David Webster
Sill with metapyroxenite at the base and meta-anorthosite at the top
David Webster
View over Ardilistry Bay from Cnoc Rhoanastil (Fairy Hill)
David Webster
Meta-anothosite (above) and metapyroxenite (below)