Coral Calcium from Okinawa, Japan, source. Low molecular weight calcium, such as calcium carbonate from coral, may potentially be absorbed intact or ionized by stomach acids. Nonosseous ionized calcium affects membrane permeability and enzyme regulation. Calcium also plays a role in cellular processes. Calcium provides nutritive support for normal, healthy bones and teeth, proper nerve impulse transmission and muscle contraction. Coral calcium is from coral grains. Coral grains are grains of the skeletal structure of reef-building coral that has become defunct. The method by which they are obtained does not destroy living coral reefs.