dolomitic limestone   Limestone is formed in an undersea environment, chiefly by animals (such as coral and shellfish) absorbing calcium carbonate out of the ocean water and using it as their exoskeleton, or framework to support their body. Over time the animals become buried, and with pressure and time becomes limestone. In special “evaporative” ocean environments, like shallow lagoons, the calcium will form gypsum (calcium sulfate) instead of limestone, and the sea water become enriched in magnesium, which combines with the calcium carbonate to form dolomite. Dolomite can also form when ground water moving through the limestone replaces calcium with magnesium. Both limestone and dolomite can contain fossil material from the original sea animals. Fond Du Lac Country Squire