Here's why:

* Cooling Rate: When magma or lava cools rapidly, the mineral crystals have less time to grow.

* Crystal Size: This results in small, often microscopic crystals, which are too small to see with the naked eye.

* Texture: The resulting texture is described as aphanitic (meaning "without visible crystals").

Examples of fine-grained igneous rocks include:

* Basalt: A dark-colored volcanic rock.

* Rhyolite: A light-colored volcanic rock.

* Andesite: An intermediate-colored volcanic rock.