We talked about igneous rocks that are formed by heat, such as from lava. We also talked about metamorphic rocks that are formed from other rocks that are altered by chemistry, heat and pressure to form a new kind of rock.
Sedimenatary rocks are the third basic rock type found on earth.
Sedimentary rocks are formed from sediments, just as the name says. Only 5 per cent of the Earth's crust consists of sedimentary rocks, yet 75 per cent of the rocks exposed at the Earth's surface are sedimentary. Weathering wears down the other rocks into silt and rain and rivers wash the silt down and deposit it in layers. Wasson's Bluff, Nova Scotia. Notice the layers of sediments.