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)Intrusive magma flows onto the Earth's surface and cools very slowly, allowing many small mineral grains to grow.
C)The extrusive magma cools quickly so the mineral grains do not have time to grow.
D)The extrusive magma, because it is deep below the surface, cools very slowly producing very small mineral grains.

Question

Quizplus · Accepted Answer

Lava flows are extrusive igneous rocks that cool rapidly on the Earth's surface. The fast cooling rate doesn't allow enough time for large mineral grains to form, resulting in finer grained rocks. In contrast, intrusive magmas are insulated by the surrounding rock, leading to slower cooling rates and the formation of larger mineral grains, resulting in coarser grained rocks.

Lava Flows Are Typically Finer Grained Than Intrusive Igneous Rocks