Hornfels

Hornfels (German, meaning "hornstone", after its frequent association with glacial "horn peaks" in the Alps, being a very hard rock and thus more likely to resist glacial action and form horn-shaped peaks such as Matterhorn) is the group designation for a series of contact metamorphic rocks that have been baked and indurated by the heat of intrusive igneous masses and have been rendered massive, hard, splintery, and in some cases exceedingly tough and durable.