The three main rock types are categorized by how they are formed. Rock types, however, are not permanent. Physical processes can change one rock type into another rock type. The process that describes how rocks are changed over time is known as the rock cycle.
The basic rock cycle showing the transformation of all three rock types.
A brief description of the basic cycle would start with magma or lava. As the magma or lava cools and hardens, it forms igneous rock. The physical process that results in the solidification of magma or lava is known as crystallization.
The igneous rock undergoes weathering and erosion, resulting in sediments being formed. These sediments are then compacted and cemented into sedimentary rock. The process of converting sediment into sedimentary rock is known as lithification.
Further geologic processes may result in this sedimentary rock being buried deep in the Earth. Intense heat or pressure resulting from other forces (i.e., mountain formation) may cause the sedimentary rock to be transformed into metamorphic rock.
Metamorphic rock may convert back into magma as a result of extreme heat. We are now back again at the “beginning” and the whole cycle may start over again.
Learning Activity – Discover the Rock Cycle
Click on the interactive animation below to start a learning activity on the rock cycle.
Interactive Animation of The Rock Cycle.