Job 41:24

His heart is as hard as a rock,
as hard as a lower millstone!

Isaiah 48:4

Because I know that you are stubborn,
and your neck is iron
and your forehead bronze,

Jeremiah 5:3

Lord, don’t Your eyes look for faithfulness?
You have struck them, but they felt no pain.
You finished them off,
but they refused to accept discipline.
They made their faces harder than rock,
and they refused to return.

Zechariah 7:12

They made their hearts like a rock so as not to obey the law or the words that the Lord of Hosts had sent by His Spirit through the earlier prophets. Therefore great anger came from the Lord of Hosts.

Treasury of Scripture Knowledge

Summary

His heart is as firm as a stone; yea, as hard as a piece of the nether millstone.

Bible References

As hard

Isaiah 48:4
Because I know that you are stubborn,
and your neck is iron
and your forehead bronze,
Jeremiah 5:3
Lord, don’t Your eyes look for faithfulness?
You have struck them, but they felt no pain.
You finished them off,
but they refused to accept discipline.
They made their faces harder than rock,
and they refused to return.
Zechariah 7:12
They made their hearts like a rock so as not to obey the law or the words that the Lord of Hosts had sent by His Spirit through the earlier prophets. Therefore great anger came from the Lord of Hosts.

Holman Christian Standard Bible®, Copyright © 1999, 2000, 2002, 2003, 2009 by Holman Bible Publishers.