obdurate
1. [ adjective ] stubbornly persistent in wrongdoing
Synonyms: obstinate unrepentant cussed
Related terms: unregenerate
2. [ adjective ] showing unfeeling resistance to tender feelings
Synonyms: stony flinty
Examples:

"the child's misery would move even the most obdurate heart"

Related terms: hardhearted
Similar spelling:   obdurately
  obturate
  obduracy
  obturator