ABSTRACT
Calcium is an alkaline earth, divalent, cationic element, abundant in the biosphere and widely distributed in nature. It exhibits intermediate solubility. As a solid, calcium forms crystalline minerals with a variety of anions, thereby making up the bulk of limestone, marble, gypsum, coral, pearls, seashells, bones, and antlers. In solution, its ionic radius (0.99 A˚ units) allows it to fit snugly into the folds of protein molecules.
