The rock cycle describes how rocks change as a result of natural processes. The rock cycle forms new rocks using the crystallization, erosion and compaction processes. This makes the correct answer: D: all of the above. Igneous rocks for example are rocks formed from the crystallization( formation of rock crystals in cooling magma) of a liquid. Sedimentary rocks are formed by erosion. However, in order to form a sedimentary rock, the accumulated sediment must become compacted and cemented together.