Final answer:
Igneous rocks are classified based on their composition and texture. Extrusive igneous rocks cool rapidly, resulting in fine-grained rocks. Intrusive igneous rocks cool slowly, leading to coarse-grained rocks.
Step-by-step explanation:
Igneous rocks are classified based on their composition and texture. The composition refers to the minerals present in the rock, while the texture refers to the features observed, such as grain size and the presence of vesicles. Extrusive igneous rocks cool rapidly, resulting in fine-grained rocks with a lack of crystal growth. On the other hand, intrusive igneous rocks cool slowly, leading to coarse-grained rocks.