Which rock is formed when molten magma or lava cools and solidifies?

Igneous rock forms when molten magma or lava cools and solidifies.

Magma is molten rock beneath Earth’s surface, while lava is magma that has erupted onto the surface. When magma cools underground, it usually cools slowly and allows larger crystals to grow; granite is a familiar intrusive igneous rock. Lava exposed at the surface cools more quickly, commonly producing fine-grained basalt or volcanic glass such as obsidian.

Igneous rocks are divided into intrusive, or plutonic, rocks and extrusive, or volcanic, rocks. The distinction is based mainly on where cooling occurs and how quickly it happens. Chemical composition also matters: basalt is relatively rich in iron and magnesium, while granite contains more silica and is generally lighter in color.

Igneous rocks are one of the three major rock groups, alongside sedimentary and metamorphic rocks. They can be weathered into sediment, buried and transformed by heat and pressure, or melted again to create new magma. Therefore, igneous formation is one stage in the global rock cycle rather than an isolated process.