My experience with black sand is from Canada only as it doesn't exist as a beach condition here in Bermuda. It is a layer of heavy iron laced sand (baslt or granite based) that is black/rust in color and is typically covered by a lighter layer of beach sand.
Any others out there with more East Coast United States experience feel free to jump in.
BDA
Any others out there with more East Coast United States experience feel free to jump in.
BDA