Here's why:

* Extrusive Igneous Rocks: These rocks form when magma (molten rock) erupts onto the Earth's surface as lava and then cools and solidifies.

* Volcanic Rocks: This is a more specific term for extrusive igneous rocks, emphasizing their origin from volcanic activity.

The rapid cooling of lava prevents large crystals from forming, resulting in rocks with:

* Fine-grained textures: Many small crystals are visible.

* Glassy textures: Some volcanic rocks cool so quickly that crystals don't even have time to form, resulting in a glass-like texture.

Examples of volcanic rocks include:

* Basalt: A dark-colored, fine-grained rock commonly found in oceanic crust.

* Rhyolite: A light-colored, fine-grained rock often associated with explosive volcanic eruptions.

* Obsidian: A glassy, black volcanic rock that cools very quickly.