Cnoc a' Chapuill
Condition (NatureScot)
| Unit | Feature | Condition | Area (ha) | Assessed |
|---|---|---|---|---|
| F1 | Mineralogy of Scotland | Favourable | — | 2009-02-17 |
Geology & landscape
Geological Feature: Igneous Intrusion, Rock Outcrop · Mining / Industrial: Quarry
Landscape processes: Volcanic / Igneous
Description
CNOC A’CHAPUILL Cnoc a’Chapuill lies 500m inland from Cairisiadar, on the west of the Isle of Lewis. It is comprised of an igneous dyke outcrop, of limited exposure, within the face of a small quarry. The dyke is composed of the ultrabasic rock ‘monchiquite’, of Tertiary age (dated at 47 million years old) and is the only one of its type so far found in the Outer Hebrides. The dyke cuts through ancient Lewisian gneisses and formed during a period of igneous activity relating to continental rifting at the opening of the North Atlantic. Inclusions in this dyke provide important information on the petrographic and geochemical nature of the Hebridean mantle. The major xenolith rock types are granulites, peridotites, pyroxenites and wehrlites whilst the megacrysts comprise clinopyroxene, mica, magnetite, rutile, apatite, sanidine, anorthoclase, corundum and zircon.