An area of rock altered in composition, structure, or texture by contact with an igneous intrusion. See Richards and Collins (2002) J. Metamorph. Geol. 20, 1. Metamorphic rocks have been changed from their original form by heat or by pressure beneath Earth’s surface; for example, limestone to marble, shale to slate, slate to schist. Dislocation metamorphism (a widespread but non-universally recognized concept—see Sobolev et al. (2002) Bull. Voronzeh State Univ. 2: Geology) occurs through friction along fault planes or thrust planes. Regional metamorphism (also called dynamic metamorphism) occurs during an orogeny; see Patison et al. (2001) Australian J. Earth Scis 48, 2.