Here's a breakdown:

* Magma: Molten rock found beneath the Earth's surface.

* Cooling: As magma rises towards the surface or intrudes into the Earth's crust, it begins to cool.

* Crystallization: As the magma cools, the minerals within it start to solidify and form crystals.

* Igneous Rocks: The solidified, crystalline mass that results from the cooling of magma.

There are two main types of igneous rocks formed by cooling magma:

* Intrusive igneous rocks: These form when magma cools and crystallizes beneath the Earth's surface. Examples include granite and gabbro.

* Extrusive igneous rocks: These form when magma erupts onto the Earth's surface (as lava) and cools. Examples include basalt and rhyolite.

So, the process of magma cooling is the fundamental process behind the formation of all igneous rocks, which make up a significant portion of the Earth's crust.