What type of rocks form when lava cools after a volcanic eruption?

igneous rocks.

Explanation:

When the volcanic eruption takes space the magma is trusted out of the vents with the release of the gas and the pressure that is build up in the rocks and the by the hot and gas are also ejected with the magma out of the earth that forms lava on the earth surface. This lava as when it cools forms many forms of igneous rocks as it has originated from the fire. As there is about 700 type of igneous rocks on earth. The extrusive and the intrusive forms are common and the hyper-basalt.