How are igneous rocks formed?

Igneous rocks are formed through the cooling and solidification of magma or lava. When magma, which is molten rock found beneath the Earth's surface, rises to the surface and erupts through a volcano, it is referred to as lava. As the lava cools, it solidifies into igneous rock. This process can occur slowly underground, resulting in coarse-grained rocks such as granite, or quickly on the surface, leading to fine-grained rocks like basalt.

Understanding that the formation of igneous rocks is closely tied to the processes of cooling and solidification helps clarify their distinction from other types of rocks. For instance, sedimentary rocks are formed from the accumulation and compaction of sediments, and metamorphic rocks arise from the transformation of existing rocks due to heat and pressure. Additionally, the erosion of metamorphic rocks does not contribute to the formation of igneous rocks but instead affects the landscape and can lead to the formation of sedimentary layers over time. Thus, the process of cooling magma is the defining characteristic of igneous rock formation.