Here's why:

* Extrusive rocks are formed when magma erupts onto the Earth's surface as lava and cools rapidly. This rapid cooling doesn't allow the minerals much time to grow large, resulting in fine-grained textures.

* Intrusive rocks, on the other hand, cool slowly underground, giving the minerals more time to grow larger crystals.

Here are some common examples of extrusive igneous rocks:

* Basalt: A dark-colored, fine-grained rock common in volcanic flows.

* Rhyolite: A light-colored, fine-grained rock with a glassy texture.

* Obsidian: A black, glassy rock that cools so quickly that it doesn't form crystals.

Let me know if you have any other questions!