especially the beautiful white ones on tropical beaches, are composed mainly of something else: the ground-down remains of seashells and corals. Indeed, if you’re on a pristine beach in the Caribbean or Hawaii, the chances are that your feet are probably sinking into parrotfish excrement: the fish eat the corals, extract the nutrients, and poop the remaining calcium carbonate on to the seabed. For the most part, the whiter and warmer the beach, the more likely it is to have come out of the bottom of a parrotfish.
