adamant vs inflexible

adamant is a noun but inflexible is not a noun.

Word	Noun	Adjective	Verb	Adverb
adamant	Yes	Yes	No	No
inflexible	No	Yes	No	No

adamant (noun)	inflexible (noun)
very hard native crystalline carbon valued as a gem

adamant (adjective)	inflexible (adjective)
impervious to pleas, persuasion, requests, reason	resistant to being bent
	incapable of change
	not making concessions
	incapable of adapting or changing to meet circumstances