Metamorphic rocks, meta- meaning change and –morphos meaning form, is one of the three rock categories in the rock cycle (see Chapter 1). Metamorphic rock material has been changed by temperature, pressure, and/or fluids. The rock cycle shows that both igneous and sedimentary rocks can become metamorphic rocks. And metamorphic rocks themselves can be re-metamorphosed. Because metamorphism is caused by plate tectonic motion, metamorphic rock provides geologists with a history book of how past tectonic processes shaped our planet .