Metamorphic came from Greek words meaning "change" and "form". Metamorphic rocks form deep in the earth where there are high temperatures, great pressure, and chemical reactions causing rocks to change from one to another. Metamorphic rocks begin to forming more than 10 kilometers beneath the earth's surface. They begin changing at temperatures of 100 degrees Celsius to 800 degrees Celsius.If you squeeze and heat a rock for a million years, it will turn into a new rock. Where does the heat come from? It comes from magma. Where does the pressure come from? From layers of rock piled on top of layers and layers of rock. The layers on the bottom get squeezed. The thicker the layers, the more pressure there is. Metamorphic rocks are classified by texture and composition, rarely have fossils, may react with acid, usually made up of different-sized crystals, rarely have pores or openings, and may be composed of only one mineral.