Colourful and patterned pebbles of igneous rocks

The colours and patterns of the pebbles on the beach at Albecq on the north coast of Guernsey in the Channel Islands reflect the varied geology of the north of the island. The northern part of Guernsey is made up of igneous rocks such as granite, diorite and gabbro and formed about 400 – 500 million years ago (de Pomerai & Robinson 1994 pp 5 & 7). Most of the pebbles in these photographs would have originated in nearby bedrock that would include Cobo Granite, Icart Gneiss, Perelle Gneiss Group, and Bordeaux Diorite Complex. These rocks are constituents of what is known as the Northern Igneous Complex. The patterns in the rocks are due to the coarse mineral crystal composition. Potassium-rich orthoclase feldspar is responsible for the recurring pink-orange colour, with light grey plagioclase feldspar; quartz grains are transparent; and biotite mica is seen as small black shiny crystals (de Pomerai & Robinson 1994 p 49).

REFERENCE

de Pomerai, M. and Robinson, A (1994) The Rocks and Scenery of Guernsey. La Societe Guernesiaise, St Peter Port, Guernsey. ISBN 0 9518075 2 8.

 

6 Replies to “Pebbles at Albecq”

  1. Thank you. Linda. I wish I could confidently say what rock type each pebble is but that would take a lot more visits to the site and in depth investigations.

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