Igneous rocks. Igneous rocks form from melted rock, called magma. On the surface of the Earth, igneous rocks usually occur in a cooled state, except where molten rock is erupting from an active volcano.Magma that flows out onto the Earth's surface is called lava. Rocks that crystallize quickly from cooling lava at or near the Earth's surface are called volcanic rocks-no surprise.gneous rocks form from melted rock, called magma. On the surface of the Earth, igneous rocks usually occur in a cooled state, except where molten rock is erupting from an active volcano.