extrusive « Back to Glossary IndexIgneous rock cooling, and thus forming, outside of the Earth, i.e. on the surface. Synonyms: volcanic rock, extrusive rockRelated Articles: Glossary: rhyoliteGlossary: intermediateGlossary: maficGlossary: ultramaficGlossary: andesite« Back to Glossary Index Author: Chris Associate Professor, Salt Lake Community College, Salt Lake City, Utah View all posts by Chris