Final answer:
Igneous rock bodies are subdivided based on their texture and chemistry. Slow cooling results in large-grained intrusive rocks, while fast cooling produces small-grained extrusive rocks.
Step-by-step explanation:
Igneous rocks are subdivided based on their texture and chemistry. The texture of an igneous rock is determined by the size of the mineral grains, which is influenced by how quickly the magma cools. Slow cooling rates result in larger grains, while fast cooling rates produce smaller grains.
Igneous rocks with large grains are called intrusive or plutonic rocks because they cool slowly within the Earth's crust. Examples of intrusive rocks include granite and diorite. On the other hand, igneous rocks with tiny grains are called extrusive or volcanic rocks. These rocks form when lava cools on the surface of the Earth. Examples of extrusive rocks include basalt and andesite.