IGNEOUS ROCKS Igneous rocks are the foundation of Earth’s crust, formed from the cooling and solidification of molten magma or lava. They are divided into two main types: intrusive igneous rocks, which cool slowly beneath the surface to form large crystals like granite, and extrusive igneous rocks, which cool quickly at the surface to form fine-grained textures like basalt. These rocks are the starting point of the rock cycle and reveal much about volcanic activity, plate tectonics, and the comp