Flow banding 3060810 215620475 2008-05-28T23:59:16Z Black Tusk 1722754 restub {{Unreferenced|date=July 2007}}[[Image:Peroxenite banding.JPG|thumb|260px|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 coins|1 euro coin]] for scale.]] '''Flow banding''' is a geological term to describe bands or layers that can sometimes be seen in rock that formed from the substance [[magma|molten rock]] or magma. Flow banding is caused by friction of the viscous magma which 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 a [[lava]] is flowing. The friction and viscosity of the magma causes [[phenocrysts]] and [[xenolith]]s within the magma or lava to slow down near the interface and become trapped in a viscous layer. This forms laminar flow, which manifests as a banded, streaky appearance. Flow banding is the result of a process of [[Fractional crystallization (geology)|fractional crystallization]] which occurs by [[convection]], if the crystals which are caught in the flow-banded margins are removed from the melt. This can change the composition of the melt in large intrusions, leading to differentiation. In [[ultramafic to mafic layered intrusions]] flow banding can occur with crystal [[cumulate rocks|accumulation]], forming pseudo-sedimentary structures. Flow banding can also occur due to disturbances in the field of flow thus forming a haemotomtic flow band, these are common in the region of upper Iceland, there are many good Icelandic videos in which this rare phenomenon can be observed. See also: * [[Cumulate rocks]] * [[Igneous differentiation|Fractional crystallization]] [[Category:Igneous rocks]] [[Category:Structural geology]] [[Category:Volcanology]] [[Category:Petrology]] {{Volcanology-stub}}