what kind of rocks are most abundant in the earth's crust
The internal structure of Earth. The crust of the Earth is composed of a great variety of igneous, metamorphic, and sedimentary rocks. The crust is underlain by the mantle. The upper part of the mantle is composed mostly of peridotite, a rock denser than rocks common in the overlying crust.The boundary between the crust and mantle is conventionally placed at the MohoroviÄiÄ discontinuity, a boundary defined by a contrast in seismic velocity.he upper part of the mantle is composed mostly of peridotite, a rock denser than rocks common in the overlying crust. The boundary between the crust and mantle is conventionally placed at the MohoroviÄiÄ discontinuity, a boundary defined by a contrast in seismic velocity.