types of rocks are formed
Rocks are categorized into three distinct types based on their method of formation. The three types are igneous, sedimentary, and metamorphic. Early in Earth's history, all rock was igneous, having formed from the cooling of melt on the surface.
1 Metamorphic Rocks-Metamorphic rocks are formed by great heat and pressure. 2  They are generally found inside the Earth's crust where there is enough heat and pressure to form the rocks. 3  Metamorphic rocks are often made from other types of rock.
Sedimentary rocks are formed from particles of sand, shells, pebbles, and other fragments of material. Together, all these particles are called sediment. Gradually, the sediment accumulates in layers and over a long period of time hardens into rock.