Flexi Says: The formation of metamorphic rock can involve both physical and chemical changes to the existing rock. Heat and pressure can cause ions to move in or out of a mineral. This is a chemical change that creates a different mineral. The new minerals that form during metamorphism are more stable in the new environment. Extreme pressure may also cause physical changes. If pressure is exerted on the rock from one direction, the rock forms layers. This is foliation. If pressure is exerted from all directions, the rock usually does not show foliation.
