1. Igneous rocks are the primary rocks formed first on the earth. These rocks are weathered, eroded, transported and deposited at some places to form sedimentary rocks.
2. The Igneous and Sedimentary rocks are changed into metamorphic rocks under the influence of temperature and pressure.
3. The metamorphic rocks are also get disintegrated and deposited to form sedimentary rocks.
4. Formation of igneous rocks take place when there is an outflow of molten materials. Like this, the rocks of the earth crust keeps on changing from one form to another form under various natural forces and agents.
5. The endless process is referred as Rock Cycle.