intrusive « Back to Glossary IndexIgneous rock cooling, and thus forming, inside of the Earth, i.e. under the surface. Synonyms: plutonic rock, plutonicRelated Articles: Glossary: graniteGlossary: dioriteGlossary: layered intrusion8 Earth HistoryGlossary: peridotite« Back to Glossary Index Author: Chris Associate Professor, Salt Lake Community College, Salt Lake City, Utah View all posts by Chris