Igneous rock that cools very quickly when it forms has a fine-grained texture.

Here's why:

* Rapid Cooling: When magma or lava cools quickly, the mineral crystals don't have enough time to grow large.

* Small Crystals: This results in many tiny crystals that are difficult to see without a microscope.

* Fine-Grained Texture: The overall appearance of the rock is described as fine-grained.

Examples of fine-grained igneous rocks include basalt, rhyolite, and andesite.