Igneous rocks are formed from the cooling and solidification of molten material called magma or lava. When magma cools slowly beneath the Earth's surface, it creates intrusive igneous rocks, like granite. Conversely, when lava cools quickly on the surface, it forms extrusive igneous rocks, such as basalt. These rocks are classified based on their mineral composition and texture. Igneous rocks can be further divided into two main types: felsic, which are rich in silica and light-colored, and mafic, which are darker and contain more iron and magnesium. They play a crucial role in the rock cycle and the formation of the Earth's crust.