Black sand can be seen as a layer on top of silica sand in regions with high wave energy, on the flanks of volcanoes, and in areas where most of the source rock is mafic, or dark-colored and poor in silica. It can be composed of a number of different dark minerals – most are iron-rich and heavier than silica sand. This weight enables it to remain when high-energy waves wash the lighter sand grains out into the surf zone.
