Final answer:
The Earth's mantle is composed mostly of peridotite, which contains iron and sulfur.
Step-by-step explanation:
The Earth's mantle is composed mostly of a very dense rock called peridotite, which contains high levels of the minerals iron and sulfur. Peridotite is also rich in magnesium and is the main rock type of the Earth's upper mantle.
Learn more about Composition of the Earth's mantle