Calcium. Polarised light micrograph (PLM) of calcium, a soft, silvery-white metal. Calcium (symbol Ca), an element from group 2A of the periodic table, is used in the manufacture of alloys and as a deoxidant in casting. It is a constituent of body fluids, bones and teeth. It is also essential for the correct functioning of the nervous system, muscle contractions and blood clotting. Magnification unknown.