'Dust' in the Bible

On the third day a man came [unexpectedly] from Saul’s camp with his clothes torn and dust on his head [as in mourning]. When he came to David, he bowed to the ground and lay himself face down [in an act of great respect and submission].

So David and his men went on the road; and Shimei went along on the hillside close beside David and cursed as he went and threw stones and dust at him.

“Then I beat them as [small as] the dust of the earth;I crushed and stamped them as the mire (dirt, mud) of the streets.