The Rock Cycle A Cycle of Many Pathways KEY CONCEPT: Forces deep inside the Earth and at the surface produce a slow cycle that builds, destroys, and changes rocks in the crust. ◊ Igneous rock is turned into sediment by erosion. The sediment is deposited and slowly becomes sedimentary rock. ◊ The sedimentary rock is buried by more sediment and heat and pressure cause it to change into metamorphic rock. ◊ Metamorphic rock is forced into the mantle and melts forming magma. Magma erupts and cools to form igneous rock again. How Does it Work? QuickTime™ and a Sorenson Video 3 decompressor are needed to see this picture.