Lava flows are typically finer grained than intrusive igneous rocks. Why?
A) Intrusive magma is cooler because it is well insulated by the surrounding rock.
B) The extrusive magma, because it is deep below the surface, cools very slowly producing very small mineral grains.
C) Intrusive magma flows onto the Earth's surface and cools very slowly, allowing many small mineral grains to grow.
D) The extrusive magma cools quickly so the mineral grains do not have time to grow.

Question

Quizplus · Accepted Answer

Extrusive magma cools quickly upon reaching the Earth's surface, which prevents the formation of large mineral grains, resulting in a finer-grained texture.

Lava Flows Are Typically Finer Grained Than Intrusive Igneous Rocks