It is written in The Zohar (p 156 [in Hebrew]): The angels Aza and Azael are from the quality of Achoraim of Abba and Ima in which GAR de Hochma illuminated in the world of Nekudim. Prior to the sin, they were largely corrected, and after the sin they returned to their annulment and they will not be corrected before the end of correction.
This means that since they are from the quality of GAR, and before the end of correction only VAK de Hochma illuminates, they will have no correction. The stony heart belongs to the correction of the inner Abba and Ima, to which the Mochin of the angels relate.