Why Do Coarse-Grained Igneous Rocks Form?

Coarse-grained igneous rocks form when magma cools slowly within Earth. ... Light-colored rocks have granitic compositions. Dark colored rocks have basaltic compositions. Dark-colored rocks that contain only olivine and pyroxene are ultramafic rocks.

Why do coarse grained igneous rocks form in the crust?

Origins of Igneous Rocks

For example, a coarse-grained, felsic igneous rock is not only a granite, it is an intrusive igneous rock that formed from slow cooling and crystallization of a body of magma within the earth's crust.

What are coarse grained igneous rocks and how do they form?

Intrusive igneous rock is formed when magma cools and solidifies within small pockets contained within the planet's crust. As this rock is surrounded by pre-existing rock, the magma cools slowly, which results in it being coarse grained – i.e. mineral grains are big enough to be identifiable with the naked eye.