Wikipedia
Black sand is sand that is black in color. One type of black sand is a heavy, glossy, partly magnetic mixture of usually fine sands, found as part of a placer deposit. Another type of black sand, found on beaches near a volcano, consists of tiny fragments of basalt.
While some beaches are predominantly made of black sand, even other colour beaches (e.g. gold and white) can often have deposits of black sand, particularly after storms. Larger waves can sort out sand grains leaving deposits of heavy minerals visible on the surface of erosion scarps.
Usage examples of "black sand".
Coming across the black sand desert, they had found sufficient water, but Snake's traps were unsuccessful.
The black sand, which sparkled and blinded in the, sunlight, at night was like a layer of soft soot.
A pile of black sand poured out upon the desk before the surprised Yukon.
He couldn't turn around in the partly submerged lava tube except just inside the weathered out, half-submerged mouth, where the black sand floor rose almost to the widest part of the tube.
The wasteland of black sand and wind-scoured rock lying out beyond the tumbled scree at the base of the pinnacle was alive with Murgo horsemen scurrying this way and that in a frenzied, disorganized search.