Calcium ( ) is the chemical element with symbol Ca and atomic number 20.

Calcium is also the fifth-most-abundant dissolved ion in seawater by both molarity and mass, after sodium, chloride, magnesium, and sulfate.

Calcium is essential for living organisms, in particular in cell physiology, where movement of the calcium ion Ca < sup > 2 +</ sup > into and out of the cytoplasm functions as a signal for many cellular processes.

Calcium, with a density of 1. 55 g / cm < sup > 3 </ sup >, is the lightest of the alkaline earth metals ; magnesium ( specific gravity 1. 74 ) and beryllium ( 1. 84 ) are more dense, although lighter in atomic mass.

Calcium has a higher electrical resistivity than copper or aluminium, yet weight-for-weight, due to its much lower density, it is a rather better conductor than either.

Calcium is the fifth-most-abundant element by mass in the human body, where it is a common cellular ionic messenger with many functions, and serves also as a structural element in bone.

Calcium, combined with phosphate to form hydroxylapatite, is the mineral portion of human and animal bones and teeth.

Calcium hydroxide ( slaked lime ) is used in many chemical refinery processes and is made by heating limestone at high temperature ( above 825 ° C ) and then carefully adding water to it.

Calcium carbonate ( CaCO < sub > 3 </ sub >) is one of the common compounds of calcium.

Calcium is not naturally found in its elemental state.

Calcium is used

* Calcium carbonate ( CaCO < sub > 3 </ sub >) is used in manufacturing cement and mortar, lime, limestone ( usually used in the steel industry ) and aids in production in the glass industry.

* Calcium hydroxide solution ( Ca ( OH )< sub > 2 </ sub >) ( also known as limewater ) is used to detect the presence of carbon dioxide by being bubbled through a solution.

* Calcium arsenate ( Ca < sub > 3 </ sub >( AsO < sub > 4 </ sub >)< sub > 2 </ sub >) is used in insecticides.

* Calcium carbide ( CaC < sub > 2 </ sub >) is used to make acetylene gas ( for use in acetylene torches for welding ) and in the manufacturing of plastics.

* Calcium chloride ( CaCl < sub > 2 </ sub >) is used in ice removal and dust control on dirt roads, in conditioner for concrete, as an additive in canned tomatoes, and to provide body for automobile tires.

* Calcium cyclamate ( Ca ( C < sub > 6 </ sub > H < sub > 11 </ sub > NHSO < sub > 3 </ sub >)< sub > 2 </ sub >) was used as a sweetening agent but is no longer permitted for use because of suspected cancer-causing properties.

* Calcium gluconate ( Ca ( C < sub > 6 </ sub > H < sub > 11 </ sub > O < sub > 7 </ sub >)< sub > 2 </ sub >) is used as a food additive and in vitamin pills.

* Calcium hypochlorite ( Ca ( OCl )< sub > 2 </ sub >) is used as a swimming pool disinfectant, as a bleaching agent, as an ingredient in deodorant, and in algaecide and fungicide.

* Calcium permanganate ( Ca ( MnO < sub > 4 </ sub >)< sub > 2 </ sub >) is used in liquid rocket propellant, textile production, as a water sterilizing agent and in dental procedures.

* Calcium phosphate ( Ca < sub > 3 </ sub >( PO < sub > 4 </ sub >)< sub > 2 </ sub >) is used as a supplement for animal feed, fertilizer, in commercial production for dough and yeast products, in the manufacture of glass, and in dental products.

Calcium carbonate is deposited by the water as a soft jelly, but this eventually hardens into travertine.

Calcium cations from hard water can also combine with soap, which would dissolve in soft water.

Calcium carbonate, long used as the coating of paper, was now being used as an important filler as the paper industry converted from acid-based paper making systems to alkaline systems.

Calcium bentonite is a useful adsorbent of ions in solution, as well as fats and oils, being a main active ingredient of fuller's earth, probably one of the earliest industrial cleaning agents.

Calcium metal reacts with water, evolving hydrogen gas at a rate rapid enough to be noticeable, but not fast enough at room temperature to generate much heat.

Calcium metal was not available in large scale until the beginning of the 20th century.

It includes metal salts which are important for processes requiring ions such as Na < sup >+</ sup > ( Sodium ), K < sup >+</ sup > ( Potassium ), Ca < sup > 2 +</ sup > ( Calcium ).

* Calcium, symbol for the chemical element ( Ca )

The question that piqued his curiosity was that how come a heavier element like Calcium is present up to a greater height compared to a lighter element like Hydrogen, apparently defying gravity.

Calcium and sulfur are also produced by weathering, but acid deposition is an important source of sulfur in many ecosystems.

Calcium and vitamin D decrease the risk of non-vertebral fractures in those with postmenopausal osteoporosis by approximately 18 %.

Calcium propionate is commonly added by commercial bakeries to retard the growth of molds.

Calcium citrate supplements can be taken with meals if dietary calcium cannot be increased by other means.

Calcium released by basalts binds up CO < sub > 2 </ sub > from the atmosphere forming CaCO < sub > 3 </ sub > acting thus as a CO < sub > 2 </ sub > trap.

* Calcium nitrate (" Norway salpeter ", " Norges salpeter " or " nitrate of lime "), a compound produced in Norway by the Birkeland – Eyde process during early 20th century

*; Calcium hypochlorite: Used by Semmelweis, as " chlorinated lime ", in his revolutionary efforts against childbed fever.

Calcium can be supplemented by adding pieces of cuttlebone to the diet, or with commercially available vitamin and mineral supplements.

Calcium ( Ca ) deficiency is a plant disorder that can be caused by insufficient calcium in the growing medium, but is more frequently a product of low transpiration of the whole plant or more commonly the affected tissue.

Calcium deficiency can sometimes be rectified by adding agricultural lime to acid soils, aiming at a pH of 6. 5, unless the subject plants specifically prefer acidic soil.

* Distal convoluted tubule: Once leaving the loop of Henle the thick ascending limb can optionally reabsorb and re increase the concentration in the nephrons .< ref > Reabsorbing and increasing the concentration is done by optionally absorbing Potassium ( K < sup >+</ sup >) and Hydrogen ( H < sup >+</ sup >) anions, while releasing water and the continued pumping out of Calcium ( Ca < sup >+</ sup >) and salt ( Na < sup >+</ sup > and Chlorine Cl < sup >-</ sup > ions ).

The repeated concentration by secretion of Calcium and salt ions is inhibited by Thiazides and catalyzed by Anti diuretic hormone and Aldosterone

Calcium participates in an intracellular signalling system by acting as a diffusible second messenger to the initial stimuli.

Calcium mediates the binding of the complexes via the terminal gamma-carboxy residues on FXa and FIXa to the phospholipid surfaces expressed by platelets, as well as procoagulant microparticles or microvesicles shed from them.

Calcium bentonite may be converted to sodium bentonite ( termed sodium beneficiation or sodium activation ) to exhibit many of sodium bentonite's properties by a process known as " ion exchange " ( patented in 1935 by Germans U Hofmann and K Endell ).

Calcium carbonate is used by living organisms to manufacture carbonaceous tests and shells.

Calcium channel blockers are also frequently used to alter heart rate, to prevent cerebral vasospasm, and to reduce chest pain caused by angina pectoris.