Here's why:

* Igneous rocks are formed from the cooling and solidification of magma (molten rock below the Earth's surface) or lava (molten rock above the Earth's surface).

* Extrusive igneous rocks form when lava erupts onto the Earth's surface, cools and solidifies relatively quickly. This rapid cooling leads to small mineral crystals and often results in a fine-grained texture.

Some common examples of extrusive igneous rocks include:

* Basalt: A dark-colored, fine-grained rock formed from the cooling of lava flows.

* Rhyolite: A light-colored, fine-grained rock formed from the cooling of highly viscous lava.

* Andesite: An intermediate-colored, fine-grained rock formed from the cooling of lava with a composition between basalt and rhyolite.

Let me know if you'd like to learn more about igneous rocks!