There are two major types of black sand. The first type is typically found in placer deposits which are formed when gravity filters small, slightly magnetic rock away from the quartz based sand. Placer deposits can occur around rivers, oceans or deep in the ground. This sand is mostly useful for panning precious materials out of, such as gold, aluminium and some magnetic material. The second kind of black sand is associated with the process of lava encountering the ocean. When the lava first cools against the ocean water, the forming lava rock is immediately releasing tiny explosions that produce a very fine "black sand". This sand can often burn people that walk on it due to the high amount of energy it absorbs from the sun.