Why does foliation form on metamorphic rocks?

Foliated metamorphic rock. Foliation forms when pressure squeezes the flat or elongate minerals within a rock so they become aligned. These rocks develop a platy or sheet-like structure that reflects the direction that pressure was applied in. Slate, schist, and gneiss (pronounced 'nice') are all foliated metamorphic rocks. read more

Metamorphic word is derived from “meta” and “morph”, where Meta means change and morph means form. Metamorphic Rocks are formed when exposed to high temperatures, pressure and chemical processes deep underground below earth’s surface. read more

Foliation in geology refers to repetitive layering in metamorphic rocks. Each layer can be as thin as a sheet of paper, or over a meter in thickness. The word comes from the Latin folium, meaning "leaf", and refers to the sheet-like planar structure. read more

Foliated metamorphic rocks are formed within the Earth's interior under extremely high pressures that are unequal, occurring when the pressure is greater in one direction than in the others (directed pressure). read more