Coral sand

Coral sand is a form of aragonite sand particles originating in tropical and sub-tropical marine environments primarily from bioerosion of limestone skeletal material of marine organisms. Often, this is due to corallivores, such as parrotfish, which excrete sand after digestion. However, the term "coral" in coral sand is used loosely in this sense to mean limestone of recent biological origin; corals are not the dominant contributors of sand particles to most such deposits. Rather, coral sand is a mix of coral and/or remnant skeletal fragments of foraminifera, calcareous algae, molluscs, and crustaceans . Because it is composed of limestone, coral sand is acid-soluble.