hornfels vs hornstone

hornfels and hornstone both are nouns.

Word	Noun	Adjective	Verb	Adverb
hornfels	Yes	No	No	No
hornstone	Yes	No	No	No

As nouns, hornfels and hornstone are synonyms defined as:

hornfels and hornstone: a fine-grained metamorphic rock formed by the action of heat on clay rocks

hornfels (noun)	hornstone (noun)
a fine-grained metamorphic rock formed by the action of heat on clay rocks	a fine-grained metamorphic rock formed by the action of heat on clay rocks