adamantine adamantine /ˌædəˈmæntiːn/

adjective

1. Impervious to pleas, persuasion, requests, reason  ( adamantine , intransigent , unbudgeable , adamant , inexorable )
   impervious to pleas, persuasion, requests, reason
    He is adamant in his refusal to change his mind
   he is adamant in his refusal to change his mind
    Cynthia was inexorable; she would have none of him
   Cynthia was inexorable; she would have none of him
    An intransigent conservative opposed to every liberal tendency
   an intransigent conservative opposed to every liberal tendency
   
2. Having the hardness of a diamond  ( adamantine )
   having the hardness of a diamond
   
3. Consisting of or having the hardness of adamant  ( adamantine )
   consisting of or having the hardness of adamant