Extrusive rock, or volcanic rock, forms from magma that erupts onto the Earth’s surface and cools rapidly, resulting in fine-grained textures. Examples include basalt, andesite, and rhyolite. Extrusive rocks are important in the study of volcanology, plate tectonics, and the interpretation of past volcanic activity.
Source Winter, J. D. (2010). “Principles of Igneous and Metamorphic Petrology.” Pearson.