* Intrusive vs. Extrusive: Igneous rocks are classified based on how they form. Intrusive rocks form when magma cools and solidifies *below* the Earth's surface. Extrusive rocks form when lava cools and solidifies *above* the Earth's surface.
* Slow Cooling: Granite forms from magma that cools slowly deep underground. This slow cooling allows for the formation of large mineral crystals, giving granite its characteristic coarse-grained texture.
* Features of Intrusive Rocks:
* Large Crystals: Due to slow cooling, intrusive rocks often have large, visible crystals.
* Plutons: Intrusive rocks are often found in large masses called plutons, which are formed from the cooling magma.
* Batholiths: Very large plutons are called batholiths.
In summary: The fact that granite cools below the Earth's surface is what makes it an intrusive igneous rock. This process allows for the formation of large crystals and the creation of underground masses like plutons and batholiths.
