* Formation: Igneous rock is formed from the cooling and solidification of magma (molten rock) or lava. Since the Earth's interior is primarily molten, this is the original source of crustal material.
* Oceanic Crust: The majority of the oceanic crust is composed of basalt, a type of igneous rock.
* Continental Crust: While continental crust is more diverse, with sedimentary and metamorphic rocks also present, igneous rocks are still a significant component. Granites, formed from the cooling of magma deep underground, are a common example.
Estimates:
* Some sources suggest that 95% of the Earth's crust is composed of igneous rock. This would include both the oceanic and continental crust.
* Other sources provide a more general estimate, stating that igneous rocks make up the majority of the Earth's crust, with sedimentary and metamorphic rocks making up the rest.
Key takeaway: Igneous rock is the foundation of the Earth's crust. While other rock types exist and are important, igneous rock plays a dominant role in its composition.
