Here's why:

* Igneous rocks are formed from the cooling and solidification of magma (molten rock) or lava. They are the most abundant type of rock found in Earth's crust.

* Sedimentary rocks are formed from the accumulation and cementation of sediments, which are derived from the weathering and erosion of pre-existing rocks. While abundant, they are less common than igneous rocks.

* Metamorphic rocks are formed when existing rocks (igneous, sedimentary, or even other metamorphic rocks) are transformed by heat, pressure, or chemical reactions.

While the exact percentage can vary depending on the region, igneous rocks generally make up a significant majority of Earth's crust.