It's not entirely accurate to say that most of the Earth's crust is made of igneous rock. While igneous rocks are a significant component, the Earth's crust is actually primarily composed of sedimentary rocks.

Here's why:

* Igneous rocks are formed from the cooling and solidification of molten rock (magma or lava). They are found in areas where volcanic activity is present or where tectonic plates collide.

* Sedimentary rocks are formed from the accumulation and cementation of sediments, which are fragments of existing rocks, minerals, and organic matter. They form over long periods of time through weathering, erosion, transportation, and deposition.

While igneous rocks are the foundation of the Earth's crust, they are often covered by layers of sedimentary rocks. These layers are formed through processes like erosion and deposition, leading to the formation of vast sedimentary basins.

Here's a breakdown of the Earth's crust composition:

* Continental Crust: Approximately 75% sedimentary rocks, 25% igneous and metamorphic rocks.

* Oceanic Crust: Mostly basalt (a type of igneous rock) with some sedimentary rocks.

Therefore, while igneous rocks play a vital role in the Earth's formation, sedimentary rocks are more abundant on the surface, covering a majority of the Earth's crust.