Answer:
The Earth's crust is formed mainly from the elements silicon and oxygen in the form of silicates and occurring as silicate rocks. Silicate minerals are abundant in all three rock types (igneous, metamorphic, and sedimentary) comprising the crust, but the crust is composed mainly of silicate rich igneous rock. The continental crust is composed of the lighter 'felsic' igneous rock (granitic in nature), higher in aluminum, sodium, and potassium; the oceanic crust is composed of the heavier, darker, 'mafic' igneous rock (largely basalt) which is higher in iron and magnesium than the continental crust.