Intrusive igneous rocks are formed from magma that cools and solidifies beneath the Earth's surface. This slow cooling process allows large crystals to develop, giving these rocks a coarse-grained texture. Common examples include granite and diorite. These rocks are typically found in large formations called plutons, which can be exposed at the surface through erosion over time. Intrusive igneous rocks play a crucial role in the Earth's geology, as they contribute to the formation of continents and provide valuable resources like minerals and building materials.