Earthwatcher's photos with the keyword: pegmatite

A rock cutting on the A838 near Laxford Bridge offers superb exposures of the cross-cutting relationships and deformational history of the Lewisian gneiss, 'Scourie' dykes and later Laxfordian granite pegmatite sheet-like intrusions. There is an information board in the lay-by opposite with diagrams and a concise explanation... ...but more details are given in Goodenough and Krabbendam (2011), below. "Grey quartzo-feldspathic gneisses show a well-developed gneissosity, dipping gently south. Dark-green to black amphibolite-bearing basic sheets also dip gently south and are approximately parallel to the gneissosity. However, detailed examination... shows that the basic sheets have cross-cutting relationships with the gneiss. The basic sheets are probably Scourie Dykes ... but have been deformed into sub-parallelism to the gneissosity by later deformation. Both the gneisses and the basic sheets are cut by a swarm of pegmatitic granite sheets, some of which show boudinage. One of the granite sheets has been dated at c. 1855 Ma." (Goodenough, K. M. & Krabbendam, M. (eds.), 2011. A geological excursion guide to the north-west Highlands of Scotland , British Geological Survey, Edinburgh. p.205)

Detail of the pegmatitic granite showing large crystals of pink feldspar and white quartz, at the 'Multi-couloured Rock Stop' at Loch na Fiacail, Sutherland.

Detail of the pegmatitic granite contact with the amphibolite Scourie Dyke at the 'Multi-couloured Rock Stop' at Loch na Fiacail, Sutherland.

This information board for the 'Multicoloured Rock Stop' is in a lay-by on the A838 near Laxford Bridge, Sutherland.

A panoramic view of the 'Multicoloured Rock Stop' taken from the lay-by on the A838 near Laxford Bridge, Sutherland. Made from 4 photos stitched together. The rock cutting offers superb exposures of the cross-cutting relationships and deformational history of the Lewisian gneiss, 'Scourie' dykes and later Laxfordian granite pegmatite sheet-like intrusions. There is an information board in the lay-by with diagrams and a concise explanation here... ... but more details are given in Goodenough and Krabbendam (2011), below. "Grey quartzo-feldspathic gneisses show a well-developed gneissosity, dipping gently south. Dark-green to black amphibolite-bearing basic sheets also dip gently south and are approximately parallel to the gneissosity. However, detailed examination... shows that the basic sheets have cross-cutting relationships with the gneiss. The basic sheets are probably Scourie Dykes ... but have been deformed into sub-parallelism to the gneissosity by later deformation. Both the gneisses and the basic sheets are cut by a swarm of pegmatitic granite sheets, some of which show boudinage. One of the granite sheets has been dated at c. 1855 Ma." (Goodenough, K. M. & Krabbendam, M. (eds.), 2011. A geological excursion guide to the north-west Highlands of Scotland , British Geological Survey, Edinburgh. p.205)