Magma that hardens within the Earth's crust is called intrusive igneous rock.

Here's a breakdown:

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

* Intrusive: Refers to the process of magma solidifying underground.

* Igneous rock: Any rock formed from the cooling and solidification of magma or lava.

Some examples of intrusive igneous rocks include granite, gabbro, and diorite.