The primary substance that makes up the Earth's crust is silicon dioxide, commonly found in the mineral quartz and in various igneous rocks. The Earth's crust is predominantly composed of lighter elements, particularly silicon and oxygen, which combine to form silicate minerals. These minerals account for the majority of the crust's composition. Other significant components include aluminum, iron, calcium, sodium, potassium, and magnesium. The crust varies in thickness, being thinner under the oceans and thicker under continental regions. Understanding the composition of the Earth's crust is crucial for fields such as geology, mining, and environmental science.