Job 41:24
Its heart is hard as rock, hard as a lower millstone.
Isaiah 48:4
I did this because I know how stubborn you are. Your neck muscles are like iron and your forehead like bronze.
Jeremiah 5:3
Lord, I know you look for faithfulness. But even when you punish these people, they feel no remorse. Even when you nearly destroy them, they refuse to be corrected. They have become as hardheaded as a rock. They refuse to change their ways.
Zechariah 7:12
Indeed, they made their heart as hard as diamond, so that they could not obey the Torah and the other words the Lord who rules over all had sent by his Spirit through the former prophets. Therefore, the Lord who rules over all had poured out great wrath.