Star Sand, found only on a few beaches in southern Japan, is made up entirely of the calcified shells of marine protozoa that once lived on the ocean floor.
Coccolithophores are single celled eukaryotic phytoplankton that synthesize intricate exoskeletons from crystals of calcium carbonate. The functions of these coccoliths are unknown, and may include buoyancy, osmotic regulation, protection from UV light, predation, or mechanical shock. When nutrient and light conditions are optimal, coccolithophores can form massive plankton blooms that are visible from space. Large numbers of these organisms can accumulate on the ocean floor forming chalk deposits such as the White Cliffs of Dover.