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Groix island, Morbihan, Brittany, France

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Locality type:Island
Name(s) in local language(s):Ile de Groix, Morbihan, Bretagne, France

Located about ten kilometers off the coast of Lorient, Groix island is the second largest (10 km long, 3 km wide) of the islands of southern Brittany, after Belle-île-en-Mer.

"For the visitor who comes to the island, the discovery of Groix is a source of magic that can not leave one indifferent. Mineralogical treasure born from a geological whim of extreme rarity on the planet, this 3700 acres and 17 villages island offers a great diversity of littoral landscapes, cultivated or wild." (groix.fr).

Groix island represents the emerged part of a 50 km long, 8 to 10 km wide belt oriented NW-SE and is constituted of high-pressure-medium to low-temperature metamorphic rocks or "blueschists".

The island presents itself as a plateau with an average altitude of 40 m in its western half, regularly descending to the South-East to an altitude of about 10 m at the Pointe des Chats. The island, therefore, offers a contrasting landscape between the West - the "Pivisy" - characterized by high cliffs (Pen Men) with deeply embedded valleys, and the East - the "Primiture" - showing low cliffs, beaches and a large rocky flat (Pointe des Chats, Locmaria harbour). A vertical line between Stanvrec and Pointe de l'Enfer approximately separating these two island parts.

The metamorphic fields of the island consist essentially of mica schists and quartz-mica albitic gneiss of clear color containing more or less continuous amphibolite levels recognizable by their darker tint. (Audren, C. et al. (1993): Notice explicative de la feuille île de Groix à 1/25000, B.R.G.M., Editions du Service géologique national.)

Groix island is also called "the garnet island" (l'île aux grenats).

Since 23rd December 1982 and under the supervision of the Ministry of Environment the natural reserve François Le Bail was created in order to
preserve the geological and mineralogical interest of the island as well as the fauna and flora. This reserve extends all along the coast between the Pointe des Chats and Locqueltas to the southeast on the one hand and between the parallel of the Pen Men lighthouse and the Beg-Melen semaphore in the North-West on the other hand.

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This page contains all mineral locality references listed on mindat.org. This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in mindat.org without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.


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Chauris, L., Le Bail, F., and Guigues, J. (1970) Minéraux de Basse-Bretagne: 52-73. Editions de la SEPNB, revue Pen ar Bed, Brest.
Pierrot, R. et al. (1980) Inventaire minéralogique de la France n°9: Morbihan: 100-113. Editions du BRGM, Orléans.
Dudek, K. and Kienast, J.R. (1989) Deerite from Ile de Groix, Brittany, France. Mineralogical Magazine: 53: 603-612.
Audren, C., Triboulet, C., Chauris, L., Lefort, J.P., Vigneresse J.L., Audrain, J., Thiéblemont, D., Goyallon, J., Jégouzo, P., Guennoc, P., Augris, C., and Carn, A. (1993) Notice explicative de la feuille île de Groix à 1/25000, B.R.G.M., Éditions du Service géologique national.

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