Final answer:
Extrusive and intrusive igneous rocks are named based on their formation processes and resulting textures. Extrusive rocks cool quickly on the Earth's surface and have a fine-grained texture, while intrusive rocks cool slowly beneath the surface and have a coarse-grained texture.
Step-by-step explanation:
Extrusive igneous rocks are appropriately named because they form when lava erupts from a volcano and cools quickly on the Earth's surface. This rapid cooling prevents the formation of large crystals, resulting in a fine-grained texture.
On the other hand, intrusive igneous rocks are formed when magma cools slowly beneath the Earth's surface, allowing for the growth of large crystals. Their coarse-grained texture is what makes the name 'intrusive' suitable for these rocks.