Question

When magma cools off Earth's surface, which type of crystalline structure is usually found?

Answer 1

Extrusive igneous rocks come from lava. Lava at the surface, is exposed to air and water which causes the molten rock to cool rapidly. Solidifying rocks at the surface cool too quickly for large crystals to form. Molecules in the lava do not have time to arrange themselves to form large crystals. Extrusive rocks have crystals that are too small to see without magnification.