Extrusive igneous rocks are typically finer grained than intrusive igneous rocks. Why?
A)The extrusive magma, because it is deep below the surface, cools very slowly producing very small mineral grains.
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)Intrusive magma is cooler because it is well insulated by the surrounding rock.

Question

Quizplus · Accepted Answer

Extrusive magma cools quickly, meaning the mineral grains don't have time to grow to larger sizes, resulting in a finer-grained texture. On the other hand, intrusive magma cools more slowly, allowing for bigger mineral grains to form, resulting in a coarser-grained texture.

Extrusive Igneous Rocks Are Typically Finer Grained Than Intrusive Igneous