What causes layering in metamorphic rocks?
The banding or layering (foliation) is caused by the massive force of pressure and high temperature which results from mountain building processes caused by plate collisions. The heat and pressure combine to realign the existing minerals from a random orientation to one of parallel orientation, thus creating the visible lines or platy cleavages found in foliated metamorphic rocks. The lines of foliation are created perpendicularly to the force being applied.
