Calcium and its carbonate

Calcium is the fifth most abundant element on the Earth and a large proportion of that is in the form of calcium carbonate. If you live in a hard water area, you will be familiar with the deposits of scale in pipes and fur in kettles caused by the decomposition, especially on heating, of soluble calcium hydrogen carbonate (bicarbonate). 

Peter Borrows explores chalk, taking us from The Clergy House floor in West Sussex, made from compacted chalk, to the tale of Cleopatra's pearl.