(1) Igneous Rock Explanation: Igneous rocks are formed through the cooling and solidification of magma (or lava). As hot, molten rock rises to the surface, it undergoes changes in temperature and pressure that cause it to cool, solidify, and crystallize. There are over 700 known types of igneous rock, the majority of which are formed beneath the surface of the Earth's crust. However, some are also formed on the surface as a result of volcanic activity.