A rather neglected element on the Association’s Periodic Table, calcium is in fact classed as a minor metal. Say ‘calcium’ and a metallic substance does not immediately spring to mind, rather a chalky powdery rock or possibly a bottle of milk. Calcium is, however, a metal in its pure form, though rarely seen in this state due to its instability. In air, calcium decomposes rapidly into calcium hydroxide and calcium carbonate. Calcium carbonate is the chalky substance we associate with calcium, with the white cliffs of Dover (see right) being composed of this compound.Picture13Although calcium is the fifth most abundant element (and 3rd most abundant metal) in the earth’s crust, present at a level of about 3% in the oceans and soil, it is never found free in nature. Calcium easily forms compounds by reacting with not only air but also with water and acid (on contact with water or acid, hydrogen gas is made in a fairly controlled manner, in comparison to the other alkali metals).