Job 41:24
His heart is as firm as a stone; yea, as hard as a piece of the nether millstone.
Cross-references
Isaiah 48:4
Parallel
Isaiah 48:4 uses 'iron sinew' and 'brass brow' to describe Israel's stubbornness, paralleling Leviathan's heart of stone.
Jeremiah 5:3
Parallel
Jeremiah 5:3 describes faces harder than rock — same hardness imagery as Leviathan's heart, applied to human obstinacy.
Zechariah 7:12
Parallel
Zechariah 7:12 speaks of hearts like adamant stone, mirroring Leviathan's heart — both symbolize unyielding hardness.