Calcium is a metallic chemical element which appears in great abundance in numerous compounds in the Earth's crust. Calcium is one of the most abundant minerals on Earth, in fact, and it is also a vital component of many living organisms, making calcium very important element of healthy nutrition. Dietary calcium can be found in a number of foods, and also in the form of vitamin and mineral supplements, for people who are at risk of calcium deficiency. In addition to being important for healthy bodies, calcium also has a wide range of industrial uses, both in pure form and in a number of compounds.

Many ancient cultures used calcium compounds for a wide number of things, although the element was not isolated in 1808. Sir Humphrey Davy, a well known chemist, managed to extract calcium from calcium chloride by passing an electrical current through the compound. The name of the element is taken from the Latin calx, for “limestone,” a reference to an abundant calcium compound found in many parts of the world.

In its pure form, calcium is a silvery, firm element which is rather malleable. It is classified with the alkaline earth metals, although it is less reactive than some of its relatives. The symbol Ca is used to identify calcium on the periodic table of elements, and the element has an atomic number of 20. When burned, calcium emits a yellow to red flame, and the elemental form will create a sort of patina when exposed to air.

Although calcium is not as reactive as some alkaline earth metals, it does readily combine with a wide range of substances. Some common things which contain calcium include limestone, gypsum, plants, and animals. Calcium is never found in an elemental form naturally; rather, it appears in a wide assortment of compounds. Pure calcium is often extracted from calcium chloride, using much the same technique that Sir Davy employed in 1808.

Calcium carbonate, one abundant compound, is used to make materials like concrete, quicklime, and cement. Other calcium compounds are used in alloys, insecticides, deodorant, fertilizer, textile production, cosmetics, lighting, and in flares. In living organisms, calcium is part of bones, teeth, and shells, among other hard body parts. It is also carried in the blood, playing an important metabolic role in the body. Most animals take efforts to ensure that they get enough calcium, combining calcium consumption with vitamin D for maximum absorption.