Metamorphic Rocks I Metamorphic rocks are formed from existing rock (sedimentary, igneous, metamorphic) by the action of heat, pressure, and chemicals. II Metamorphism- the process of forming metamorphic rocks within the lithosphere, making the rocks more dense and less porous. a) Recrystallization- is the process of increasing the size of the mineral crystals and/or changing the mineral composition without melting. b) Foliation- parallel layers of minerals caused by pressures on the rock. c) Two Types: 1) Regional metamorphism- when large areas of rock are under intense heat and pressure causing them to change form. (results in foliation) 2) Contact metamorphism occurs when hot magma forces its way into overlying rock and bakes the rocks in contact with it. a)Change in the rock is less drastic (no foliation) and less rock is affected then in regional.