The rock cycle is the transformation of one type of rock to another through heat, pressure, weathering and erosion. First proposed by James Hutton in the late 18th century, the cycle is an ongoing process that affects the rock that composes mountains as well as rock deep below the Earth’s surface. However, it is important to realize that not all rocks go through every stage of the cycle.
Igneous rock is often recognized as a starting point for the cycle. It forms when magma cools, either above or below ground, and solidifies into crystal form. If the igneous rock is above the surface, weather and erosion can break the rock up into sediments. Time and pressure cement the pieces together into sedimentary rock. If it is located below the Earth’s crust, igneous rock can become metamorphic rock. It must be heated to a temperature of 300 to 700 degrees Celsius for this transformation to occur. This change can also be accomplished by heat generated by tectonic plate movement.
Through heat and pressure, sedimentary rock can also change into metamorphic rock. Weathering and erosion can render sedimentary rock into igneous rock. Metamorphic rock can melt into magma and become igneous rock; it can also go through a weathering and compaction process to become sedimentary rock.