Complex sentence: Intrusive igneous rocks are formed from magma that cools and solidifies within the crust of a planet, surrounded by pre-existing rock (called country rock), the magma cools slowly, and as a result these rocks are coarse grained.
Split into simpler sentences: Intrusive igneous rocks are formed from magma that cools and solidifies within the crust of a planet. Surrounded by pre-existing rock (called country rock), the magma cools slowly, and as a result these rocks are coarse grained.