Obdurate

Obdurate means stubborn or persistent and usually refers to wrong-doing, such as a hardened criminal might exhibit. Nevertheless, it is also used in describing someone who has become resistant to emotions and or is just hard-hearted and stubborn. Obdurate comes from the Latin "to harden." -dur in the middle of the word can be found in other words such as durable which also conotates to hardness or toughness.