<p>To me it looks like a <a href="https://en.wikipedia.org/wiki/Mylonite" rel="nofollow noreferrer">mylonite</a>, 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.</p>

CC BY-SA 4.0
2023-07-22T11:47:39.437Z
Alternatively, it could also be a migmatite, another type of metamorphic rock, but I don't think so.
Jean-Marie Prival
CC BY-SA 4.0
2023-07-22T11:46:33.897Z
2023-07-23T06:53:50.840Z
2023-07-23T06:53:50.840Z
Jean-Marie Prival
<p>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?</p>
<p><a href="https://i.sstatic.net/1WD5z.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/1WD5z.jpg" alt="enter image description here" /></a></p>
<p>Location: <a href="https://www.google.com/maps/place/43.562885,-6.306475/data=!4m6!3m5!1s0!7e2!8m2!3d43.5628849!4d-6.3064748999999996?utm_source=mstt_1&amp;entry=gps&amp;lucs=47068615&amp;g_ep=CAESCTExLjg3LjMwMxgAINeCAyoINDcwNjg2MTVCAkVT" rel="nofollow noreferrer">Playa la Gairúa, Spain</a></p>

<plate-tectonics><geologic-layers>
Do these rock layers correspond to different years?
Jaime Caffarel
# Do these rock layers correspond to different years?

(Asked by: username_0 on 2023-07-22)

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?

[![enter image description here](https://i.sstatic.net/1WD5z.jpg)](https://i.sstatic.net/1WD5z.jpg)

Location: [Playa la Gairúa, Spain](https://www.google.com/maps/place/43.562885,-6.306475/data=!4m6!3m5!1s0!7e2!8m2!3d43.5628849!4d-6.3064748999999996?utm_source=mstt_1&entry=gps&lucs=47068615&g_ep=CAESCTExLjg3LjMwMxgAINeCAyoINDcwNjg2MTVCAkVT)

**Tags:** plate-tectonics, geologic-layers


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## 1 answers

### Answer by username_1 on 2023-07-22. Score: 6 | Accepted answer

To me it looks like a [mylonite](https://en.wikipedia.org/wiki/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.

> **Comments:**
> **username_1**: Alternatively, it could also be a migmatite, another type of metamorphic rock, but I don't think so.  

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