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I made a video about what I learnt in my A Level Geology course so far, about igneous rocks.

One thing I mentioned was that flow banding is mostly only found in silicic rocks (and so mostly rhyolite) because that's what the textbook says.

However, someone commented that this may not be true, so I'm curious - what rocks can / does flow banding occur in?

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Flow banding can occur in all igneous rocks, regardless of their composition. Any kind of molten rock that flows may eventually cause some flow banding. Sometimes the flow banding is not even obvious to the eye and can only be detected using geophysical methods such as magnetic anisotropy.

Here's an example of flow banding in a mafic rocks from Skaergaard intrusion in Greenland:

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This looks like a sedimentary rock, but it's in fact igneous. Those are layers of minerals such as olivine, pyroxene and plagioclase that settled from a melted magma chamber.

It doesn't even have to be a silicate rock, here's a picture of natrocarbonatite lava from Ol Doinyo Lengai volcano in Tanzania:

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Obviously, this rock exhibits flow banding and it hardly has any silica in it.

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  • $\begingroup$ I would debate whether the Skaergaard example could be classified as flow banding. It is certainly layered but this layering results from settling of different types of crystals rather than from flow. $\endgroup$ – bon Dec 13 '16 at 10:19
  • $\begingroup$ @bon vertical setting of crystals is becoming an outdated idea. Horizontal in-magma-chamber "sedimentary" processes are being increasingly recognised in all large mafic intrusions. This is especially true for the Bushveld, where most of the research is being done but it's also correct for others. $\endgroup$ – Gimelist Dec 13 '16 at 20:40

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