Here's why:

* Igneous rocks are formed from the cooling and solidification of magma (underground) or lava (above ground).

* Extrusive rocks are formed when lava erupts onto the Earth's surface and cools rapidly. This rapid cooling leads to small crystals and a fine-grained texture.

Examples of extrusive igneous rocks:

* Basalt: A common dark-colored rock found in volcanic regions.

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

* Obsidian: A dark, glassy rock that cools so quickly that crystals don't have time to form.

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