Extrusive igneous rocks form when lava hardens and cools.
Extrusive igneous rocks are types of igneous rocks that form when hot magma from inside the earth extrudes to the surface as lava which hardens and cools immediately to form small crystals. Some lava can also cool immediately to form an amorphous glass. Examples of extrusive igneous rocks include rhyolite, andesite, obsidian, basalt, pumice, scoria, tuff and dacite.
