'Harder' in the Bible

Jehovah, Thine eyes, are they not on stedfastness? Thou hast smitten them, and they have not grieved, Thou hast consumed them, They have refused to receive instruction, They made their faces harder than a rock, They have refused to turn back.

As an adamant harder than a rock I have made thy forehead; thou dost not fear them, nor art thou affrighted before them, for a rebellious house are they.'