Here's why:
* Slow cooling: Intrusive rocks form when magma cools and solidifies slowly beneath the Earth's surface. This slow cooling process allows the minerals in the magma to have ample time to grow into large, well-defined crystals.
* Large crystals: The larger the crystals, the coarser the texture. This is why intrusive rocks are often described as having a phaneritic texture, meaning the crystals are visible to the naked eye.
In contrast, extrusive igneous rocks, which cool rapidly on the Earth's surface, have a fine-grained texture because their crystals are small.
