The mantle is the mostly solid bulk of Earths interior, lying between Earths dense, super-heated core and its thin outer layer, the crust. The rocks that make up Earth’s mantle are mostly silicates, which are a wide variety of compounds that share a silicon and oxygen structure. Common silicates found in the mantle include olivine, garnet, and pyroxene. The other major type of rock found in the mantle is magnesium oxide. Other mantle elements include iron, aluminum, calcium, sodium, and potassium. In terms of its constituent elements, the mantle is made up of 44.8% oxygen, 21.5% silicon, and 22.8% magnesium. There’s also iron, aluminum, calcium, sodium, and potassium. These elements are all bound together in the form of silicate rocks.