Extrusive igneous rocks are typically finer grained than intrusive igneous rocks. why? extrusive igneous rocks are typically finer grained than intrusive igneous rocks. why? the extrusive magma, because it is deep below the surface, cools very slowly producing very small mineral grains. the extrusive magma cools quickly so the mineral grains do not have time to grow. intrusive magma is cooler because it is well insulated by the surrounding rock. intrusive magma flows onto the earth's surface and cools very slowly, allowing many small mineral grains to grow.

The correct answer is - The extrusive magma cools quickly so the mineral grains do not have time to grow.

The extrusive igneous rocks are on of the two large groups of igneous rocks, the hardest rocks, and the ones that give the basis for the formation of the sedimentary and metamorphic rocks afterwards.

The name itself, extrusive, tells us where this rocks are formed, outside, or rather on the surface. The extrusive igneous rocks are formed from the magma flows on the surface of the Earth. Because the temperature on the surface of the Earth is significantly lower than the magma, the magma is cooling off very quickly. Because of the very quick cooling off of the magma, the extrusive igneous rocks are forming very quickly, which also results in them being fine-grained. Their crystals are very small, in some cases almost unnoticeable, and the reason for that is that the mineral grains simply do not have enough time to grow larger because of the very quick cooling off of the magma and quick formation of these rocks.