Igneous rocks form when molten rock, known as magma, cools and solidifies. This process can occur beneath the Earth's surface, resulting in intrusive igneous rocks, or above the surface during volcanic eruptions, leading to extrusive igneous rocks. The cooling rate affects the rock's texture; slow cooling produces larger crystals, while rapid cooling results in smaller crystals. The composition of the magma influences the type of igneous rock created. For example, granite is a common intrusive rock with a coarse texture, while basalt is a fine-grained extrusive rock. These rocks are essential for understanding Earth's geological processes.