Here's why:
* Extrusive igneous rocks form when magma (molten rock) erupts onto the Earth's surface as lava and cools quickly. This rapid cooling often results in fine-grained textures. Examples include basalt, rhyolite, and obsidian.
* Intrusive igneous rocks form when magma cools and solidifies beneath the Earth's surface. The slow cooling process allows for the formation of larger crystals, giving these rocks a coarse-grained texture. Examples include granite, gabbro, and diorite.
So, the same type of magma can form different types of igneous rocks depending on where it cools and the rate at which it cools.
