Flow banding

[1] Flow banding is caused by friction of the viscous magma that is in contact with a solid rock interface, usually the wall rock to an intrusive chamber or, if the magma is erupted, the surface of the Earth across which the lava is flowing.

This forms laminar flow, which manifests as a banded, streaky appearance.

This can change the composition of the melt in large intrusions, leading to differentiation.

In layered intrusions, flow banding can occur with crystal accumulation, forming pseudo-sedimentary structures.

You can help Wikipedia by expanding it.This article about structural geology is a stub.

Flow-banded rhyolite in the Dunn Point Formation ( Ordovician ) exposed near Arisaig, Nova Scotia.
Flow banding at the rim of a peridotite intrusion . Dark and green pyroxenite bands at the bottom represent the melt, brownish lherzolite bands at the top the solid phase. Near Midsund , Norway , 1 euro coin for scale.