Have you ever tried to observe sand from close-up? With a good magnifying glass or even better with a microscope, for example. You would find wonderful surprises in a kaleidoscope of tiny, colourful rocks. These are very small shells belonging to a wide variety of marine organisms. Foraminifera are protozoa, single-celled organisms equipped with shells that have many different shapes depending on the species. Diatoms are also single-celled organisms equipped with microscopic shells but, unlike foraminifera, they are algae and carry out photosynthesis. There are beaches in the world famous for sand rich in spectacularly shaped shells. On Iriomote Island in Japan is Star Sand Beach, an expanse of sand filled with the remains of star-shelled foraminifera.