Part of the EASP Geology Walk Hornfels is a metamorphic rock formed by a special type of metamorphism called contact metamorphism. This means that a rock (clay rich in this case) comes into contact with an igneous intrusion so the rock heats up but no pressure is exerted. Because of this, hornfels is nonfoliated; there is no pressure to force the minerals into layers. Hornfels can vary widely in both appearance and mineral composition, which both depend on the composition of the parent rock. The grains of the rock are very small and fit closely together. Department of Earth, Atmospheric, and Planetary Sciences
