hornstone vs metamorphic rock

hornstone and metamorphic rock both are nouns.

Word	Noun	Adjective	Verb	Adverb
hornstone	Yes	No	No	No
metamorphic rock	Yes	No	No	No

As nouns, metamorphic rock is a hypernym of hornstone; that is, metamorphic rock is a word with a broader meaning than hornstone:

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

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