Dubh Loch, Colonsay
Geological Conservation Review site | GCR #2937 | Igneous Petrology | Carboniferous - Permian Igneous
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.
Summary
This locality exposes the Kilchatten monchiquite, a dyke of Permo- Carboniferous age, which is noteworthy for the diverse range of phenocrysts and xenoliths found within it.
Many of the xenoliths are coarse-grained and it is clear that they are disaggregated fragments of rocks of lower crustal and mantle derivation, including pegmatitic glimmerite, pyroxenite and peridotite. Megacrystic minerals of note are biotite, kaersutite, clinopyroxene and apatite. These xenolith assemblages provide a critical insight into the character of the deep crust and mantle below Scotland during Permo- Carboniferous times, and the site is of high scientific research interest. The dyke is also significant historically in being one of the earliest rocks to be dated radiometrically in 1941.
