Facts About Calcium
Calcium is essential for building healthy teeth and strong bones.
Credit: ipag | Shutterstock

Calcium is nature's most renowned structural material. Indeed, calcium is a necessary component of all living things and is also abundant in many non-living things, particularly those that help support life, such as soil and water. Teeth, sea shells, bones and cave stalactites are all products of calcium. 

Interestingly, calcium seems to come in fifth place wherever it goes: It is the fifth most abundant element by mass in the Earth's crust (after oxygen, silicon, aluminum and iron); the fifth most abundant dissolved ion in seawater (after sodium, chloride, magnesium and sulfate); and the fifth most abundant element in the human body (after oxygen, carbon, hydrogen and nitrogen). It is, however, the most abundant metallic element in the human body, 99 percent of which can be found in our bones and teeth (about 2 lbs. of it!), according to Chemicool

In its pure elemental state, calcium is a soft, silvery-white alkaline earth metal. It is important to note, however, that calcium is never found in this isolated state in nature, but exists instead in compounds. Calcium compounds can be found in a variety of minerals, including limestone (calcium carbonate), gypsum (calcium sulfate) and fluorite (calcium fluoride), according to Chemicool. Calcium makes up about 4.2 percent of the Earth's crust by weight.

In order to isolate pure calcium, it must be extracted through electrolysis, a technique that uses a direct electrical current to separate elements from their naturally occurring sources. Once isolated, calcium is quite reactive and will form a grayish-white oxide and nitride coating when exposed to air.

Calcium (Ca) is No. 20 in the periodic table of the elements, appearing just below magnesium in the same column (Group IIA) as the other alkaline earth metals (a group of metals that are more chemically reactive than most metals). Calcium comes from the Latin word "calx," meaning lime. This is not a reference to the fruit, but rather calcium oxide (CaO), the useful building material derived from heated limestone. 

In 1808, Cornish chemist and inventor Sir Humphry Davy was the first person to successfully isolate calcium. A few other scientists, Magnus Pontin and Jöns Jacob Berzelius, had come close; they had been able to produce a calcium amalgam after performing electrolysis on a mixture of lime and mercury oxide. This time, Davy repeated their electrolysis method on the same calcium amalgam, but he added more lime to the mixture, producing more of the amalgam from which he was able to distill away the mercury, leaving only calcium, according to the Royal Society of Chemistry.

Once calcium had been successfully isolated, the element was able to be studied further, revealing its importance for the survival of all living things.

  • Atomic number (number of protons in the nucleus): 20
  • Atomic symbol (on the periodic table of the elements): Ca
  • Atomic weight (average mass of the atom): 40.078
  • Density: 1.55 grams per cubic centimeter
  • Phase at room temperature: solid
  • Melting point: 1,548 degrees Fahrenheit (842 degrees Celsius) 
  • Boiling point: 2,703 F (1,484 C)  
  • Number of isotopes (atoms of the same element with a different number of neutrons): 24; 5 stable
  • Most common isotopes: Ca-40 (97 percent of natural abundance); Ca-44 (2 percent of natural abundance); Ca-42 (0.6 percent of natural abundance); Ca-48 (0.2 percent of natural abundance); Ca-43 (0.1 percent of natural abundance); Ca-46 (0.004 percent of natural abundance.

Calcium is extremely important to the human body. Not only is it vital for bones and teeth, but it assists in muscle movement by carrying messages from the brain to all our body parts. Cells in all living things must communicate with, or "signal," one another. Calcium ions act as vital messengers between these cells and are necessary in all multicellular life forms. They also assist in the release of hormones and enzymes.

In food, calcium is found in mineral form. Foods high in calcium include dairy products — such as milk, cheese and yogurt — and some vegetables, such as kale, watercress, spinach and broccoli. In order for calcium to absorb properly, it should be taken with vitamin D. Magnesium is also necessary for proper assimilation and use of calcium in the body. In fact, if we take too much calcium and not enough magnesium, it can cause problems in the body.

  • Lime, or calcium oxide, produces a brilliant, intense light when exposed to an oxyhydrogen flame, according to Chemicool. In the 1800s, before electricity was invented, this substance was used to light up the theater so actors truly performed "in the limelight" — hence the saying.
  • When turtles (typically pet turtles) don't have enough calcium circulating through their blood, they may get an ailment called Metabolic Bone Disease, commonly known as Soft Shell Syndrome. For a turtle to be healthy, the calcium to phosphorous ratio should be 2:1. When their calcium levels are low, however, the mineral is leached from their bones in the body's attempt to balance things out. The result is soft bones, weakness and a soft, deformed shell, and it often results in death. The disease can be prevented with a proper diet and adequate sunlight (or other appropriate lighting for reptiles). 
  • Stalactites and stalagmites, the icicle-shaped formations found in underground caverns, are formed slowly over time by the build-up of calcite residue. This occurs when water seeps through the cracks in the ceiling of a limestone cave, dissolving and carrying along traces of calcite, the building material of limestone. As the water drips from the ceiling, this calcite residue begins to build up at the site of the drip, eventually resulting in icicle-shaped stalactites hanging from the cave ceiling. This water dripping from the stalactites then forms stalagmites on the ground below.
  • Many nutritionists recommend a calcium-magnesium ratio of 2:1. But although our bodies require more calcium, we are actually more likely to become deficient in magnesium. This is because our bodies tend to store and recycle calcium, while magnesium gets used or excreted and must be replenished on a daily basis. 
  • Calcium carbonate is the active ingredient in many antacids, such as Tums and Rolaids. The alkaline compound works by neutralizing the stomach acid responsible for heartburn and indigestion.

Not only is calcium essential for human life, but it is also an essential nutrient for plant growth. In most types of soils, calcium is made available to plants through the weathering of minerals. As an alkaline earth metal, calcium plays a vital role in controlling soil pH (potential of hydrogen), a measure of the soil's acidity or alkalinity. 

The availability of calcium can indirectly affect many microbial processes that are sensitive to soil pH, such as decomposition, nitrogen mineralization and nitrification, said Feike A. Dijkstra, a biogeochemist and associate professor at the Centre for Carbon, Water and Food at the University of Sydney.

Calcium is typically abundant in most soils with some areas having naturally higher or lower levels of calcium. "High levels of calcium in the soil are usually found in arid and semi-arid regions where potential evapotranspiration is larger than actual rainfall," Dijkstra told Live Science. "Certain plants have adapted to calcium-rich and alkaline soils, and are called calcicoles. In contrast, calcifuges are plants that thrive in calcium-poor and acidic soils." 

Problems can occur when there is a pH imbalance in the soil. Soil with an overabundance of calcium can result in the pH being too high (above 7), or alkaline, and this sometimes "reduces the solubility of nutrients such as phosphate and many micro-nutrients, which can then limit plant growth," Dijkstra explained. The bigger problem, however, typically lies in soil with too little calcium, as this results in soil acidification. This can happen when calcium is leached out of the soil through heavy rain or even more problematic — acid rain.

"During the 1970s and 1980s acid rain was a major problem affecting many forests in northeastern America and Europe," Dijkstra said. "When acid rain reaches the soil, the protons of these strong acids in acid rain replace calcium cations on the exchange sites, and the calcium is leached out of the soil profile."

"Acid rain killed many forests because the associated soil acidification resulted in increased solubility of aluminum. Aluminum is toxic to plants when it gets above certain concentrations in the soil," he said. "Since the Acid Rain Program established under the 1990 Clean Air Act, acid rain has become less of a problem for forests in the northeastern U.S."

Calcium compounds have a wide variety of uses, particularly in the making of construction materials. Gypsum, or calcium sulfate, is used in making plaster and also "plaster of Paris," a heavy white powder that, when mixed with water, hardens into a cast to set fractured bones. 

Limestone, or calcium carbonate, is used directly as construction material and indirectly for cement. When limestone is heated it releases carbon dioxide, leaving behind quicklime (calcium oxide). When quicklime is mixed with water, it creates slaked lime (calcium hydroxide) which is used to make cement. Slaked lime is also used as a soil conditioner and as a water treatment agent to reduce acidity. When mixed with sand, slaked lime pulls in carbon dioxide from the air and hardens into lime plaster, according to the Royal Society of Chemistry.

Pure calcium metal is used as a reducing agent in the preparation of other types of metals, such as thorium and uranium and zirconium. It can also be used as an alloying agent for aluminum, copper, lead and magnesium alloys, or as a deoxidizer, desulfurizer and decarburizer for a variety of ferrous and nonferrous alloys.

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