What is the main difference between intrusive and extrusive igneous rocks?

The distinction between intrusive and extrusive igneous rocks primarily lies in their cooling processes. Intrusive igneous rocks form when magma cools and solidifies slowly beneath the Earth's surface. This prolonged cooling period allows crystals to grow larger, resulting in a coarse-grained texture. Examples include granite and diorite, which are characterized by their visible mineral crystals.

On the other hand, extrusive igneous rocks form when lava cools quickly once it reaches the Earth's surface. This rapid cooling doesn’t allow for significant crystal growth, leading to a fine-grained texture or even a glassy appearance in some cases, as seen in rocks like basalt or obsidian.

Understanding this primary difference highlights how the environment of formation impacts the physical characteristics of the rocks, including texture and mineral composition. The other choices either misstate the cooling rates or misunderstand the mineral content, which does not affect the fundamental definitions of intrusive and extrusive rocks.