Igneous Intrusive Defined

Intrusive igneous rocks crystallize within the crust interior.

Intrusive igneous rocks (also called plutonic rocks, named after Pluto, the Roman god of the underworld) are formed from magma that cools and hardens within the earth. Surrounded by pre-existing rock (called country rock), the magma cools slowly, and as a result these rocks are coarse grained. The mineral grains in such rocks can generally be identified with the naked eye.

The central cores of major mountain ranges consist of intrusive igneous rocks, usually granite. When exposed by erosion, these cores (called batholiths) may occupy huge areas of the surface.

Coarse grained intrusive igneous rocks which form at depth within the earth are termed as abyssal; intrusive igneous rocks which form near the surface are termed hypabyssal.

(Taken from Wikipedia...)