Pink Aplite Veins in L’Eree Granite

Numerous pink veins ranging in width from 10 cm to 1 metre in thickness pass through the northern part of the outcrop of L’Erée Granite in the Channel Island of Guernsey (De Pomerai & Robinson 1994). These are made of aplite. When the hot magma had nearly completely cooled and crystallised to form what we know today as the L’Eree Granite, “residual fluids escaped along cracks in the rock, depositing their dissolved load as they cooled down”.

Aplite is defined as:

a light coloured, fine-grained, equigranular igneous rock composed of subhedral to anhedral grains of quartz and alkali feldspar, and found as late-stage veins in granite bodies. The quartz-alkali feldspar composition corresponds to the lowest temperature melts in granite magma systems, suggesting that they are residual melts formed by the differentiation of granite magma. The lack of any hydrous minerals and the fine grain size points to the aplites crystallising from dry residual melts.

(Oxford Dictionary of Earth Sciences)

REFERENCES

Allaby, M. (2008) A Dictionary of Earth Sciences, Oxford Paperback Reference, Oxford University Press, 3rd Edition, ISBM 978-0-19-921194-4.

British Geological Survey Classical areas of British geology: Guernsey, Channel Islands Sheet, 1 (Solid and Drift) Scale 1:25,000. NERC, Crown Copyright 1986.

De Pomerai, M. and Robinson A. 1994 The Rocks and Scenery of Guernsey, illustrated by Nicola Tomlins, Guernsey: La Société Guernesiaise, ISBN 0 9518075 2 8, page 32.

Roach, R. A., Topley, C. G., Brown, M., Bland, A. M. and D’Lemos, R. S. 1991. Outline and Guide to the Geology of Guernsey, Itinerary 9 – Jerbourg Peninsula, . Guernsey Museum Monograph No. 3, Gloucestershire: Alan Sutton Publishing. ISBN 1 871560 02 0, pages 11 & 75.