The surface of Arrakis consisted almost exclusively of dry dune deserts. The Sand of Arrakis comes in many forms and sizes including boulders, rocks, pebbles, pea gravel, flaked rocks, pea-sand, sand, flour-sand, and dust. Sand on Arrakis is mostly a product of worm digestion; dust (the truly omnipresent problem there) is produced by the constant surface creep, the “saltation” movement of sand. Coarse grains are found on the downwind sides of dunes. The windward side is packed smooth and hard. Old dunes are yellow (oxidized), young dunes are the color of the parent rock—usually gray.
Flour-Sand is a common place for Fremen to pitch their stilltents, due to the sand’s softness
Travelers must be wary of other forms like a Dust Chasm - any deep crevasse or depression on the desert of Arrakis that has been filled with dust not apparently different from the surrounding surface; a deadly trap because human or animal will sink in it and smother. The sand can also come in different forms such as Drum Sand - a condition of sand compaction. The slightest step sets it drumming.