Calcium (Ca) is a chemical element belonging to the alkaline-earth metals in Group 2 of the periodic table. It is the most abundant metallic element in the human body and the fifth most abundant in the Earth's crust. Calcium does not occur naturally in its free state, but its compounds are widely distributed. The silvery, soft, lightweight metal was first isolated in 1808 by Sir Humphry Davy. The name calcium comes from the Latin word for lime, calx . Calcium is essential to both plant and animal life, and the human body is 2% calcium. Major sources of calcium in the human diet are milk, milk products, fish, and green leafy vegetables.

Where do we find calcium in nature?

Calcium, a silvery, soft metal, is abundant in nature, but it doesn't occur naturally in its free state. It's a key component of the Earth's crust (3.64%) and the Moon's crust (8%). Calcium is found in: * Minerals: calcite (limestone, chalk, marble, dolomite), fluorite, anhydrite, aragonite, gypsum, feldspars, and zeolites * Biological sources: eggshells, pearls, coral, stalactites, stalagmites, shells of marine animals, teeth, and bones * Water: natural waters, including the sea, where calcium carbonate deposits dissolve to form calcium bicarbonate It is also essential for plant and animal life. The human body is 2% calcium, which we can get from milk, milk products, fish, and green leafy vegetables.

Why is calcium important for living things?

Calcium is vital for living organisms because it serves as a structural element, signal transducer, and enzyme cofactor. In humans, calcium is the most abundant inorganic element. Calcium is essential for: * Bone and teeth structure About 99% of the body’s calcium is stored in bones and teeth, providing strength and rigidity. * Neuromuscular function It is needed for muscle contraction, nerve impulse transmission, and regulation of heartbeat. * Other processes Calcium is also involved in blood clotting, hormone secretion, enzyme function, and milk production. Dietary sources of calcium include milk, dairy products, green leafy vegetables, and fish. Insufficient calcium intake can lead to diseases such as rickets and osteoporosis.

How does calcium help our bodies grow and stay healthy?

Calcium is crucial for the human body. It is the main element that supports bones and teeth , with calcium salts making up about 70% of bone by weight, providing strength and rigidity. Beyond its structural role, calcium is essential for: * Muscle contraction * Nerve impulse transmission * Blood clotting * Hormone secretion * Enzyme function The body tightly regulates calcium levels in the blood to ensure proper function. Vitamin D and hormones like parathyroid hormone and calcitonin help maintain calcium balance by controlling absorption, storage in bones, and excretion. A prolonged mild deficiency can lead to osteoporosis , while severe deficiency can cause tetany.

What common foods are rich in calcium?

Foods rich in calcium include dairy products like milk , cheese , and yogurt . Leafy green vegetables such as broccoli , turnips , and collard greens are also good sources. Seafood like salmon and sardines can provide substantial amounts of calcium as well. Calcium is crucial for healthy bones and teeth, muscle contraction, nerve transmission, and hormone regulation. The U.S. Food and Drug Administration recommends 1,300 mg of calcium per day for adults and children over 4 years old.

How is calcium used in industries and products besides food?

Beyond its well-known role in food and dietary supplements, calcium and its compounds play significant roles across various industries. Calcium carbonate is used as a filler in products like paper, plastic, ceramics, glass, and paint. Calcium oxide (quicklime) is a key ingredient in building materials and is also used in steel manufacturing. Calcium hydroxide is used in the construction industry in mortar, plaster, and cement. It is also used to treat wood in the paper industry and to remove hair and fats from animal hides in leather production. Additionally, calcium is used as an alloying agent for metals like aluminum and magnesium, enhancing their properties. In steelmaking, calcium is used to remove sulfur, improving the steel's physical properties.

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A labeled diagram of the periodic table entry for calcium, showing its atomic number 20, symbol Ca, atomic weight 40.078, electron configuration, and classification as an alkaline-earth metal. Icons indicate calcium is a solid with a face-centered cubic crystal structure and strongly basic oxides at room temperature.

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Discover how calcium and carbonate dissolved in seawater serve as the building material for seashell construction

At a Glance

calcium summary

calcium

chemical element

Also known as: Ca

Written by

Timothy P. Hanusa

Fact-checked by

Britannica Editors

Last updated

Nov. 9, 2026 •History

News •

Taking calcium and vitamin D may not prevent broken bones • Nov. 2, 2026, 2:00 PM ET (Washington Post)

calcium (Ca), chemical element, one of the alkaline-earth metals of Group 2 (IIa) of the periodic table. It is the most abundant metallic element in the human body and the fifth most abundant element in Earth’s crust.

Element Properties
atomic number	20
atomic weight	40.078
melting point	842 °C (1,548 °F)
boiling point	1,484 °C (2,703 °F)
specific gravity	1.55 (20 °C, or 68 °F)
oxidation state	+2
electron configuration	1s²2s²2p⁶3s²3p⁶4s²

Occurrence, properties, and uses

calciteCalcite, the most common form of natural calcium carbonate (CaCO₃). It is a widely distributed mineral known for the beautiful development and great variety of its crystals.

Calcium does not occur naturally in the free state, but compounds of the element are widely distributed. One calcium compound, lime (calcium oxide, CaO) was extensively used by the ancients. The silvery, rather soft, lightweight metal itself was first isolated (1808) by Sir Humphry Davy after distilling mercury from an amalgam formed by electrolyzing a mixture of lime and mercuric oxide. The name for the element was taken from the Latin word for lime, calx.

Calcium constitutes 3.64 percent of Earth’s crust and 8 percent of the Moon’s crust, and its cosmic abundance is estimated at 4.9 × 10⁴ atoms (on a scale where the abundance of silicon is 10⁶ atoms). As calcite (calcium carbonate), it occurs on Earth in limestone, chalk, marble, dolomite, eggshells, pearls, coral, stalactites, stalagmites, and the shells of many marine animals. Calcium carbonate deposits dissolve in water that contains carbon dioxide to form calcium bicarbonate, Ca(HCO₃)₂. This process frequently results in the formation of caves and may reverse to deposit limestone as stalactites and stalagmites. As calcium hydroxyl phosphate, it is the principal inorganic constituent of teeth and bones and occurs as the mineral apatite. As calcium fluoride, it occurs as fluorite, or fluorspar. And as calcium sulfate, it occurs as anhydrite. Calcium is found in many other minerals, such as aragonite (a type of calcium carbonate) and gypsum (another form of calcium sulfate), and in many feldspars and zeolites. It is also found in a large number of silicates and aluminosilicates, in salt deposits, and in natural waters, including the sea.

Formerly produced by electrolysis of anhydrous calcium chloride, pure calcium metal is now made commercially by heating lime with aluminum. The metal reacts slowly with oxygen, water vapour, and nitrogen of the air to form a yellow coating of the oxide, hydroxide, and nitride. It burns in air or pure oxygen to form the oxide and reacts rapidly with warm water (and more slowly with cold water) to produce hydrogen gas and calcium hydroxide. On heating, calcium reacts with hydrogen, halogens, boron, sulfur, carbon, and phosphorus. Although it compares favourably with sodium as a reducing agent, calcium is more expensive and less reactive than the latter. In many deoxidizing, reducing, and degasifying applications, however, calcium is preferred because of its lower volatility and is used to prepare chromium, thorium, uranium, zirconium, and other metals from their oxides.

The metal itself is used as an alloying agent for aluminum, copper, lead, magnesium, and other base metals; as a deoxidizer for certain high-temperature alloys; and as a getter in electron tubes. Small percentages of calcium are used in many alloys for special purposes. Alloyed with lead (0.04 percent calcium), for example, it is employed as sheaths for telephone cables and as grids for storage batteries of the stationary type. When added to magnesium-based alloys in amounts from 0.4 to 1 percent, it improves the resistance of degradable orthopedic implants to biological fluids, permitting tissues to heal fully before the implants lose their structural integrity.

Concept artwork on the periodic table of elements.

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Naturally occurring calcium consists of a mixture of six isotopes: calcium-40 (96.94 percent), calcium-44 (2.09 percent), calcium-42 (0.65 percent), and, in smaller proportions, calcium-48, calcium-43, and calcium-46. Calcium-48 undergoes double beta decay with a half-life of roughly 4 × 10¹⁹ years, so it is stable for all practical purposes. It is particularly neutron-rich and is used in the synthesis of new heavy nuclei in particle accelerators. The radioactive isotope calcium-41 occurs in trace quantities on Earth through the natural bombardment of calcium-40 by neutrons in cosmic rays.

Calcium is essential to both plant and animal life and is broadly employed as a signal transducer, enzyme cofactor, and structural element (e.g., cell membranes, bones, and teeth). A large number of living organisms concentrate calcium in their shells or skeletons, and in higher animals calcium is the most abundant inorganic element. Many important carbonate and phosphate deposits owe their origin to living organisms.

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The human body is 2 percent calcium. Major sources of calcium in the human diet are milk, milk products, fish, and green leafy vegetables. The bone disease rickets occurs when a lack of vitamin D impairs the absorption of calcium from the gastrointestinal tract into the extracellular fluids. The disease especially affects infants and children.

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Occurrence, properties, and uses

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