High or moderately high pressures during metamorphism can create rocks with distinct layers called
foliation, including slate, schist and gneiss. Foliation makes some rocks stripy, like mylonite, migmatite
and glaucophane schists, and makes others, like phyllite, liable to split into thin sheets. Foliation means
either that some minerals have been separated into bands, or that crystals have been aligned in parallel.