Lava Flows Are Typically Finer Grained Than Intrusive Igneous Rocks

question 74

Multiple Choice

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.

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