hornfels

Borrowed from German Hornfels, literally "horn stone", after its frequent association with glacial "horn peaks" in the Alps.

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hornfels (countable and uncountable, plural hornfelses or hornfels)

1. Any of a series of contact metamorphic rocks that have been baked and indurated by the heat of intrusive igneous masses and rendered massive, hard, splintery, and in some cases exceedingly tough and durable.