Earth is approximately 4.6 billion years old and has come a long way from the huge spinning cloud of dust and gas it formed from. The planet is now comprised of three main sections: the core, mantle and crust. Silica is a mineral compound made of silicon and oxygen, SiO2, and is found on the Earth’s crust in three main crystalline varieties: quartz, tridymite and cristobalite.
Layers of Crust
The Earth’s crust can be further broken down into two categories -- the oceanic crust and continental crust. The oceanic crust is 3 to 6 miles thick, while the continental crust is 22 to 44 miles thick. Even though the oceanic layer is thinner, it is more dense and heavier than the continental layer. However, you will find more silica on the continental crust.