Black sand
From LSWiki
From the pile of stuff at Xordigath's altar west of Stillwater
Sometimes I've seen it in Shatterspire
On the speedwalk between Losthaven and Tlax or Stormrock, somewhere in the 236se section on a beach: You fly southeastward. a sandy island [compass, compass:up, compass:down, u] You see a handful of black sand. You fly southeastward.