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Marchlyn Mawr, Llanberis, Gwynedd (Caernarvonshire), Wales, UK

UK Grid Reference: SH616619
Latitude: 53°8'9"N
Longitude: 4°4'8"W

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The natural lake Marchlyn Mawr has been dammed to form the upper reservoir of the Dinorwig Pumped Storage Scheme, the largest pumped storage hydroelectric scheme in Europe at the time of its construction in 1984 (see also Dinorwig Quarry, the site of the lower reservoir).

Fibrous, radiating aggregates of thomsonite occur here infilling vesicles to 20 mm in diameter in the Marchlyn Dyke; an olivine dolerite of Palaeogene age.

Refs:
Williams, D., 1930. The geology of the country between Nant Peris and Nant Ffrancon (Snowdonia). Quarterly Journal of the Geological Society of London, 86, 191-232.
Williams, D., 1924. On two olivine-dolerite dykes in Snowdonia. Proceedings of the Liverpool Geological Society, 14, 38-47.

Mineral List

Thomsonite-Ca

1 entry listed. 1 valid mineral.

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Copyright © Jolyon Ralph and Ida Chau 1993-2011. Site Map. Locality, mineral & photograph data are the copyright of the individuals who submitted them.Further information contact the Site hosted & developed by Jolyon Ralph. Mindat.org is an online information resource dedicated to providing free mineralogical information to all. Mindat relies on the contributions of hundreds of members and supporters. Mindat does not offer minerals for sale. If you would like to add information to improve the quality of our database, then click here to register. Current server date and time: 16th Jun 2011 15:26:13