Gneiss: nm Gneiss is a crystalline rock as dense as granite. It contains quartz, mica, feldspar. Its origin is methamorphic following an evolution of the rock by tectonic pressure and temperature. Its foliation is marked by layers generally of dark tint alternating with light beds. Gneiss is a grapevine rock very present in Provence (Massif des Maures), Alsace, Anjou, in the Nantes region, etc ....
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