black diamond vs adamant

black diamond and adamant both are nouns.

Word	Noun	Adjective	Verb	Adverb
black diamond	Yes	No	No	No
adamant	Yes	Yes	No	No

As nouns, adamant is a hypernym of black diamond; that is, adamant is a word with a broader meaning than black diamond:

black diamond: an inferior dark diamond used in industry for drilling and polishing
adamant: very hard native crystalline carbon valued as a gem

Other hypernyms of black diamond include diamond.

black diamond (noun)	adamant (noun)
an inferior dark diamond used in industry for drilling and polishing	very hard native crystalline carbon valued as a gem

black diamond (adjective)	adamant (adjective)
	impervious to pleas, persuasion, requests, reason