New Living Translation
Its heart is hard as rock, hard as a millstone.

American Standard Version
His heart is as firm as a stone; Yea, firm as the nether millstone.

Berean Study Bible
His chest is as hard as a rock, as hard as a lower millstone!

Douay-Rheims Bible
His heart shall be as hard as a stone, and as firm as a smith's anvil.

English Revised Version
His heart is as firm as a stone; yea, firm as the nether millstone.

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

World English Bible
His heart is as firm as a stone, yes, firm as the lower millstone.

Young's Literal Translation
His heart is firm as a stone, Yea, firm as the lower piece.

Job 41:24 Additional Translations ...