The rock cycle is the process by which the planet recycles and changes one kind of rock into another continuously.
The three types of rocks involved in the rock cycle are igneous rocks, sedimentary rocks and metamorphic rocks.
Metamorphic rock is rock deep beneath the Earth’s surface that is under intense heat and pressure. Metamorphic rock can melt, become magma and cool into igneous rock or become exposed and through weathering and erosion become sedimentary rock.
Igneous rock is made up of magma from volcanoes that has reached the surface and cooled until it is stone. Igneous rocks can become heated through various processes and once again become metamorphic rock or, through weathering and erosion, be broken down into sediment that becomes compacted and becomes sedimentary rocks.
Sedimentary rock is rock that–through compacting and cementing–is made up of pieces of igneous and metamorphic rock. Through erosion and weathering it can break up again and become sediment to be compacted again or it can transition to metamorphic rock due to heat and pressure.
In terms of geology, nothing happens “quickly.” It may take many hundreds, thousands or even millions of years to make it through the entire cycle.