Multiple choice When the molten magma cools down inside the earth's crust, it is called ___ rock. Intrusive igneous rock Extrusive igneous rock Basalt rock Marble rock Reveal answer Fill a bubble to check yourself A Correct answer Explanation When molten magma cools slowly deep inside the Earth's crust, it forms intrusive igneous rocks (such as granite). In contrast, magma that cools on the Earth's surface forms extrusive igneous rocks.