Like sodium, potassium always occurs combined with other elements. It is found in the form of minerals such as carnallite and sylvite. Potassium is an abundant element and makes up nearly 2.5 per cent of the earth's crust. Large deposits of potassium chloride and potassium sulfate are found in Canada and Germany. The Dead Sea is another source of potassium compounds.
Potassium nitrate is used in producing matches and explosives.
Calcium Calcium is a chemical element with the symbol Ca. It belongs to a group called the alkaline earth metals. It makes up about 3.5 per cent of the earth's crust. In nature, it occurs only as compounds such as calcium carbonate, calcium fluoride and calcium sulfate. Calcium fluoride and calcium sulfate are used in making cement and plaster.