Metamorphic rocks are rocks that have changes because of changes int temperature and pressure of hot, watery fluids. These types of rocks can form from changes in igneous, sedimentary or other metamorphic rocks. Metamorphic rock forms when pre-existing rock changes resulting from high temperatures and pressures. These changes occur in the rock while it remains solid (without melting). The changes can occur while the rock is still solid because each mineral is stable only over a specific range of temperature and pressure. If a mineral is heated or compressed beyond its stability range, it breaks down and forms another mineral. In a metamorphic rock, one mineral changes to another when its atoms move about in the solid state and recombine to form new minerals. This change from one mineral to another is called metamorphism. As temperature and pressure increase, the rock gains energy. As temperature and pressure decrease, the rock cools; often, it does not have enough energy to change back to a low temperature and low-pressure mineral. The rock is stuck in a state that is characteristic of its earlier high temperature and high-pressure environment.
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