Here's why:

* Intrusive igneous rocks form when magma (molten rock) cools and solidifies *below* the Earth's surface.

* Slow cooling allows for the formation of larger crystals. This is because the atoms have more time to arrange themselves into a more ordered structure.

Here are some examples of intrusive igneous rocks:

* Granite: Known for its large, visible crystals.

* Gabbro: A dark-colored rock with a coarser texture than basalt.

* Diorite: A medium-colored rock with a granular texture.

In contrast, extrusive igneous rocks form when lava (molten rock) cools and solidifies *on* the Earth's surface. This rapid cooling results in smaller crystals or even a glassy texture.