The transformation of one type of rock into another, under suitable conditions is referred to as the rock cycle. For example, igneous rocks are formed by solidification of molten magma. These rocks may break down into smaller pieces. These smaller rock particles may then be transported and deposited under several layers of rocks to form sedimentary rocks. Similarly, sedimentary and igneous rocks transform into metamorphic rocks when subjected to extreme heat and pressure. Under the effect of heat and pressure, the metamorphic rocks break down to form sedimentary rocks or igneous rocks.