The element calcium is a basic building block within ourselves and within our environment. Building materials that contain calcium include limestone, marble, plaster, gypsum, and human bone. Although calcium minerals have been used in construction since antiquity, the metal itself is quite reactive and was only discovered in 1808.
By 1808, English chemist Humphrey Davy had already discovered sodium and potassium, two alkali metals in the left column of the periodic table. He was perhaps most famous, though, for having popularized laughing gas and made it safer through purification. Davy's next challenge was the alkaline earths, which we now know contain magnesium, calcium, strontium, and barium. But, his several efforts at isolating the metals were frustrating rather than successful.
Davy then received a letter from Swedish chemist Jöns Jakob Berzelius and Dr. M.M. af Pontin describing a new method involving mercury. Berzelius had produced a metal amalgam. Davy carried this one step further and produced an impure version of the new metal, calcium.
Mining and Production
Calcium is quarried. Many common rocks contain calcium, including limestone, gypsum, and marble. Such rocks are often used intact, for example as dimension stone, without extracting the calcium. Alternatively, calcium minerals such as apatite, chalk, and dolomite may be powdered and purified for use, still without isolating the element.
Actual metallic calcium is rarely used, but it can be prepared from calcium chloride, a substitute for road salt. (Calcium chloride can be produced from limestone, calcium carbonate.) Calcium chloride, a salt, is soluble in water, and so the metal can be obtained by electrolysis.
Properties and Uses
Calcium is a shiny silver metal, which surprises many people who associate calcium with chalk or limestone. It is soft and light. Calcium is rather reactive, though not as reactive as lithium or sodium. The metal reacts slowly with air or water and so should be stored in mineral oil.
One niche application of calcium is in pellet or powder form. Dropped into water, the calcium steadily generates hydrogen gas. Although there are other ways to generate hydrogen, this method is portable and reasonably safe.
Calcium forms many compounds and so is widely used in industry. Limestone in powder form can be heated to turn it into quicklime. Quicklime (calcium oxide) reacts vigorously with water, generating heat and producing slaked lime (calcium hydroxide). Quicklime is therefore a portable source of heat as well as a drying agent. Slaked lime is a cement.
Calcium carbonate as previously mentioned is used as a road salt. It is believed to be less harsh on the environment than regular salt. Calcium carbonate is another dessicant, as it absorbs water. When added to swimming pool water, it prevents calcium in the surrounding cement from being dissolved.
Calcium in biology is one of the essential minerals required by humans and animals. Calcium phosphate is the basis for bone, horn, shell, and other hard parts of organisms.
Because it is essential in the diet, calcium is safe to ingest or be exposed to in various forms. Calcium citrate is a food preservative. Calcium cyclamate is an artifical sweetener, no longer used in the United States. Calcium carbonate in pill or tablet form is an antacid and also sold as a dietary supplement.
The list of good dietary sources of calcium starts with dairy products such as milk and cheese. Various nuts, seaweed, and leafy green vegetables contain calcium. Other foods, such as soy milk and tofu, are fortified with calcium for the benefit of vegetarians and those who cannot eat dairy products.
The role of gypsum in agriculture is noted elsewhere.