The type of rock formed when magma forces itself into surrounding underground rock is called intrusive igneous rock.

Here's why:

* Igneous rocks are formed from the cooling and solidification of magma or lava.

* Intrusive refers to the fact that the magma cooled and solidified *inside* the Earth's crust, rather than erupting onto the surface.

Examples of intrusive igneous rocks include:

* Granite

* Diorite

* Gabbro

* Peridotite