Extrusive igneous rocks form on the Earth’s surface when magma escapes from the interior and erupts as lava, followed by cooling and solidification. This volcanic activity typically occurs at mid-ocean ridges, volcanic islands, and continental hotspots. As the lava cools quickly upon exposure to the atmosphere or water, the resulting rocks tend to have a fine-grained texture.
For instance, basalt is a common extrusive rock that forms from the rapid cooling of lava flowing from volcanoes. Conversely, if the lava cools slowly, it may form intrusive igneous rock instead. The rapid cooling in extrusive environments allows minerals in the lava to crystallize quickly, producing smaller crystals compared to those in intrusive rocks, which cool slowly below the surface.