An even more stark view of the dark blue Tongue of the Ocean whose depths reach up to 1,800 m (6,000 ft). By comparison, the waters of the Bahama Platform (light blue) are frequently less than 15 m (50 ft) deep. They are warm and become extremely salty due to evaporation and limited circulation from the open ocean. Crystals of aragonite, a calcium carbonate mineral derived from the shells of single-celled marine organisms, and direct precipitation, form into oolites (small spherical grains of limestone) as the tidal currents swirl back and forth. Lithification of the carbonate sands produces an oolite limestone. Although the water is warm and clear, corals do not live in these shallows, probably because of the salt content. Though chemically very similar, the rocks resulting from this precipitating process have a quite different origin from those formed from coral reefs. Image courtesy of NASA.