The Rock Cycle


Staff member
Jun 3, 2020
The rock cycle is a concept that describes transition of rocks among igneous, sedimentary and metamorphic rocks. The rock types won't remain forever, but keep changing. The magma or lava solidifies to form igneous rocks, the weathering and deposition of pre-existing rocks lead to formation of sedimentary rocks, and the metamorphism of rocks under high pressure and temperature leads to the formation of metamorphic rocks. When the rocks melt, they become magma, and the cycle continues. The following image clearly depicts the rock cycle.

the rock cycle

The currently existing rocks may melt & solidify to become igneous rocks, eroded & deposited to become sedimentary rocks, or metamorphose to become metamorphic rocks. The study of environment and the conditions of formation of a rock are major areas of interest in the subject Petrology.

The role of Plate Tectonics
The movement of tectonic plates lead to the destruction of crust, accelerated erosion or the mantle upwelling. These processes influence the rock cycle to a great extent as the existing rocks melt, erode or deform, and the new rocks form. The plate tectonics are also responsible for the deformation of crust which leads to the formation of several surface features like mountains, gorges, volcanoes etc. They eventually contribute to the formation of rocks.

The role of water
The water plays an important role in the rock cycle. The water serves as an agent of transportation of weathered and eroded material, helps in dissolving rocks and minerals, and plays a key role in melting crustal rocks in the wedge above the subduction zone.

Transition to igneous rock
When rock pushes deep into the earth’s surface. it melts into magma .when magma moves up and cools. It solidifies and forms igneous rock. if it cools inside the earth’s surface it called intrusive or plutonic rock. magma cools very slowly within the earth’s surface and forms coarse-grained textures such as granite. If magma(which is called lava when it reaches the surface) erupts on the surface it forms rocks called extrusive or volcanic cools very rapidly so it is fine-grained and sometimes it cools very rapidly that no crystal form results in natural glass such as obsidian. The most common rock formed is basalt. all three types of rocks melt and form igneous rocks.

Transition to a metamorphic rock
When the rock is under high temperature and pressures it changes its physical or chemical composition and forms metamorphic rock..3 factors cause a change in temperature and pressure: Weight of the overlying layer of sediment. Stress due to plates colliding. Stress due to plates sliding past each other.

When rock contact with igneous intrusion, it heats up surrounding rocks, and change its composition this metamorphism is called contact metamorphism. this metamorphism heats up and recrystallizes and alters the rocks. regional metamorphism effect on large areas associated with mountain building. these rocks commonly show bands of mineralogy and color. Any rock can be modified by the process of metamorphism.

Transition to sedimentary rock
Weathering and erosion of exposed rock break into smaller particles and transport it away from parent rock. These fragment material accumulate in the basin and is buried by additional material. sedimentary rocks form by the lithification of these buried materials. If the sediment is buried deeply, it becomes compacted and cemented, forming clastic sedimentary rock. Biologic sedimentary rocks form when large numbers of living things die. Chert is an example of this type of rock.

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