Here's why:

* Plutonic rocks are formed from magma that cools and solidifies slowly beneath the Earth's surface. This slow cooling allows for the formation of large crystals.

* Volcanic rocks are formed from lava that erupts onto the Earth's surface and cools quickly. This rapid cooling results in smaller crystals.

Granodiorite has a characteristic coarse-grained texture due to its slow crystallization process underground, making it a plutonic rock.