When you pick up a handful of beach sand, it is easy to imagine that every grain began as a piece of rock. In many places, that is essentially true: weathering, erosion and sediment transport gradually break down rocks into smaller particles that rivers, waves and wind move toward the coast. But some beaches have a very different origin. Their sand is produced partly, or even predominantly, from the hard remains of marine organisms.
Scientists call this material biogenic sediment. Coral skeletons, mollusk shells, sea urchin parts, calcareous algae and the microscopic shells of foraminifera can all eventually become sand-sized particles.
