hornstone
horns·tone
noun
1.
a fine-grained metamorphic rock formed by the action of heat on clay rocks
Origin
From horn + stone, translation of hornfels.
Related words
Broader terms
WordNet 2.1 (Princeton University). Wiktionary (CC BY-SA). WordNet 2.1 Copyright Princeton University. All rights reserved. Wiktionary content is available under the Creative Commons Attribution-ShareAlike Licence.