“Dust” and “ashes” are referred to frequently in the same Biblical contexts, so much so that some scholars have suggested that the two words are synonymous and interchangeable.
For example, the Bible describes the mourner as throwing dust on his head (Joshua 7:6; Job 2:12; Lamentations 2:10), or using ashes for the same purpose (2 Samuel 13:19; see also Jeremiah 6:26).
Sometimes the two words are used together, as in Ezekiel 27:30:
They throw dust on their heads
And sprinkle themselves with ashes.
Or when Abraham confesses to the Lord that he is but “dust and ashes” (Genesis 18:27), and when Job complains that God has cast him down like “dust and ashes” (Job 30:19). Mourners are also described as sitting on ashes (Jonah 3:6), or in the dust (Isaiah 47:1), but obviously, in both cases, sitting on the ground.