The mantle is the mostly solid bulk of Earths interior, lying between Earths dense, superheated core and its thin outer layer, the crust. The rocks that make up Earths mantle are mostly silicates, which are compounds that share a silicon and oxygen structure. The mantle is about 2,900 kilometers (1,802 miles) thick, and makes up 84 percent of Earths total volume. The mantle is predominantly solid, but it behaves like a viscous fluid due to the fact that temperatures are close to the melting point in this layer. The mantle is composed of solid peridotite, which is a type of rock that is rich in oxygen, magnesium, silicon, and aluminum. The other major types of rocks found in the mantle include olivine, garnet, and pyroxene. Other mantle elements include iron, calcium, sodium, and potassium. The mantle is divided into several layers: the upper mantle, the transition zone, the lower mantle, and D” (D double-prime), the strange region where the mantle meets the outer core.