What is the composition of earths mantle?
The mantle is 82% of Earth's volume. It is composed of ultramafic rock called peridotite, which is hot enough to flow.
The divide between the crust and the mantle is based on the composition of the rocks. The igneous rocks of the crust are of a mafic to felsic (low silica to high silica) composition, with oceanic crust dominated by basalt and contintental rock dominated by granitic rock. The mantle consists of ultramafic (very low silica) rock, with the upper portion consisting largely of a rock called peridodite.