- flinty, obdurate, stony - showing unfeeling resistance to tender feelings; "the child's misery would move even the most obdurate heart"
Antonyms: softhearted, soft-boiled (indirect, via hardhearted)
- flinty, granitic, unyielding - having austere inflexibility; "a flinty manner"; "granitic morality"; "his unyielding mouth and glassy eyes"- Marchette Chute
Antonym: flexible (indirect, via inflexible)