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

Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust.

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, phosphorus and iron are present in worthwhile amounts, and eleven other minerals also have been found in varying trace amounts.

Calcium has four stable isotopes (< sup > 40 </ sup > Ca, < sup > 42 </ sup > Ca, < sup > 43 </ sup > Ca and < sup > 44 </ sup > Ca ), plus two more isotopes (< sup > 46 </ sup > Ca and < sup > 48 </ sup > Ca ) that have such long half-lives that for all practical purposes they also can be considered stable.

Calcium also has a cosmogenic isotope, radioactive < sup > 41 </ sup > Ca, which has a half-life of 103, 000 years.

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

* Calcium, a common electrolyte, but also needed structurally ( for muscle and digestive system health, bone strength, some forms neutralize acidity, may help clear toxins, provides signaling ions for nerve and membrane functions )

Calcium channel blockers have been used to treat Alzheimer ’ s disease with some success, and the use of lithium to decrease IP < sub > 3 </ sub > turnover has also been suggested as a possible method of treatment.

Calcium and zinc also limit iron absorption.

Calcium is also required at other points in the coagulation cascade.

Calcium sulfonates additives are also added to protect motor oil from oxidative breakdown and to prevent the formation of sludge and varnish deposits.

* Calcium hydroxide, also known as " cal "

Calcium channel blockers such as verapamil may also be an effective treatment for manic symptoms but are seldom prescribed for this purpose.

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

Calcium carbide is also used for ripening fruit artificially in some countries.

Calcium also causes the release of Acetylcholine from Pre-synaptic terminal in the transmission of nerve impulse.

Calcium regulates transport of other nutrients into the plant and is also involved in the activation of certain plant enzymes.

Studies in Chembur has also found high levels of Copper, Chromium, Calcium, Arsenic and Mercury in ground water.

Anadenanthera peregrina, also known as Yopo, Jopo, Cohoba, Mopo, Nopo, Parica or Calcium Tree, is a perennial tree of the Anadenanthera genus native to the Caribbean and South America.

He also appeared in boxing film The Calcium Kid.

Calcium may also be supplemented.

Calcium also may be added at a minimum of 960 milligrams per pound.

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

There is also a fossa ovalis in the interatrial septum, which is used in the fetal period as a means of bypassing the lung. The atrium is depolarized by Calcium.