Here's why:

* Extrusive means the magma erupted onto the surface.

* Cooling happens rapidly because of the exposure to air and water.

* Crystallization occurs as the molten rock solidifies.

Examples of extrusive rocks include:

* Basalt (formed from lava flows)

* Rhyolite (formed from explosive eruptions)

* Andesite (formed from intermediate eruptions)

Let me know if you have any other questions!