A geological formation created by magma is known as an igneous rock. This occurs when magma cools and solidifies, either below the Earth's surface as intrusive igneous rocks (like granite) or on the surface as extrusive igneous rocks (like basalt). The cooling rate influences the crystal size in the rocks; slower cooling allows larger crystals to form, whereas rapid cooling results in smaller, finer crystals. These formations give insights into the Earth's geological history, the processes that shape our planet, and the dynamics of tectonic activity, offering valuable information for geologists and earth scientists.