Metamorphic rock

Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causing profound physical or chemical changes. During this process, the rock remains mostly in the solid state, but gradually recrystallizes to a new texture or mineral composition. The protolith may be an igneous, sedimentary, or existing metamorphic rock. Metamorphic rocks make up a large part of the Earth's crust and form 12% of the Earth's land surface. They are classified by their protolith, their chemical and mineral makeup, and their texture. They may be formed simply by being deeply buried beneath the Earth's surface, where they are subject to high temperatures and the great pressure of the rock layers above. They can also form from tectonic processes such as continental collisions, which cause horizontal pressure, friction, and distortion. Metamorphic rock can be formed locally when rock is heated by the intrusion of hot molten rock called magma from the Earth's interior. The study of metamorphic rocks (now exposed at the Earth's surface following erosion and uplift) provides information about the temperatures and pressures that occur at great depths within the Earth's crust. Some examples of metamorphic rocks are gneiss, slate, marble, schist, and quartzite. Slate and quartzite tiles are used in building construction. Marble is also prized for building construction and as a medium for sculpture. On the other hand, schist bedrock can pose a challenge for civil engineering because of its pronounced planes of weakness. Metamorphism Metamorphic rocks form one of the three great divisions of rock types. They are distinguished from igneous rocks, which form from molten magma, and sedimentary rocks, which form from sediments eroded from existing rock or precipitated chemically from bodies of water. Metamorphic rocks are formed when existing rock is transformed physically or chemically at elevated temperature, without actually melting to any great degree.