Christine Garner, age 14, of Lowell, Mass., for her question:
WHERE DOES CALCIUM COME FROM?
Calcium is a soft, silvery white metal element that combines easily with air, water and many other substances. It is never found in nature in a pure metallic state. Most calcium is combined with carbon and oxygen to form calcium carbonate.
Among the familiar things made of calcium carbonate are limestone, marble, seashells, eggshells and chalk. Hard water is usually caused by calcium carbonate that has dissolved.
Both plants and animals need calcium for growth and health. It is important in forming healthy bones and teeth. The hard parts of your bones are mostly calcium phosphate. More than half of the weight of the bones in your body, as a matter of fact, is calcium phosphate.
Because so much of the body is made of calcium phosphate, it is important that the diets of children include enough of this element for proper growth. Adults need it too because bones wear out and must be constantly rebuilt.
In addition to its uses in building teeth and bones, calcium is needed in the blood in order to make the muscles of the body work properly. Scientists have found also that clots will not form in a wound unless the blood has the proper amount of calcium.
Medical experts say that you receive all the calcium your body needs if you eat a proper diet. Foods rich in calcium include fruits, vegetables and milk.
Calcium is found combined with such elements as sulphur, phosphorus and boron to form many additional compounds. From these combinations come paints, medicines and even fertilizers.
The most important calcium compounds used for building materials are limestone, lime, plaster of Paris, travertine and portland cement.
Calcium is the fifth most plentiful element in the earth's crust. It has an atomic weight of 40.08 and a valence of 2. Its atomic number is 20.
Calcium is a natural builder. At one time, limestone and marble deposits were part of the ocean floor. During great upheavals of the earth these deposits were raised above sea level. Rain water with dissolved carbon dioxide soaked into these deposits and dissolved some of the calcium carbonate to change it into calcium biocarbonate.
As more of the limestone was dissolved, large underground caves were formed. As the water containing calcium biocarbonate continued to drip from the roof to the floor of a cave, some of the water evaporated, some of the carbon dioxide was released, and calcium carbonate was left on the roof and floor. In this way, stalactites and stalagmites were built in caves.
Calcium carbonate in the form of chalk is used for writing on blackboards and chalkboards.
Another calcium compound is calcium hypochlorite which is used for bleaching cotton goods and for disinfecting. It is made by the action of chlorine gas on slaked lime.
Some water purification plants use lime to neutralize the acid in water.