Igneous rocks are formed from the solidification of molten material called magma or lava. They are classified into two main types: intrusive, which cools slowly beneath the Earth's surface, and extrusive, which cools quickly on the surface. Common examples include granite for intrusive and basalt for extrusive rocks. These rocks play a crucial role in the Earth's geology, influencing landscapes and providing valuable resources. Igneous rocks can also contain minerals like quartz and feldspar, which are important for various industrial applications. Understanding igneous rocks helps geologists learn about the Earth's history and processes.