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This is a close picture of a cliff in the north coast of Spain. As you can see, the rock is composed of multiple thin layers, alternating between dark and light materials. Could this be the result of anual freeze-thaw cycles of a glacier of something like that? I mean, each layer could roughly correspond to a year?

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Location: Playa la Gairúa, Spain

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To me it looks like a mylonite, a type of metamorphic rock formed by intense ductile deformation. This deformation breaks the original minerals, which then recrystallize as small grains along the shear planes, resulting in this foliation. I've seen mylonites during a field trip at Cap de Creus, in the North of Spain, they look like your photo.

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  • $\begingroup$ Alternatively, it could also be a migmatite, another type of metamorphic rock, but I don't think so. $\endgroup$ Jul 22, 2023 at 11:47

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