Types of Metamorphic Rocks Metamorphic rock types are rocks that are formed by the process of metamorphism in pre-existing rocks. The rock of origin can be igneous, sedimentary or metamorphic. The process of metamorphism is a process that causes changes in the mineral composition, texture and structure of rocks due to heat and high pressure, as well as active chemical solutions. When plate motion pushes igneous or sedimentary rock deep into the earth, high pressure and temperature compresses and crushes…