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

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 where evaporation of the water leaves a solution supersaturated with the chemical constituents of calcite.

Calcium carbonate has two forms, the stable calcite, and the metastable aragonite, which is stable within a reasonable range of chemical environments but rapidly becomes unstable outside this range.

* Calcium carbide, a chemical compound

* Calcium, symbol for the chemical element ( Ca )

In the early 19th century Ignacy Fonberger, a professor at the University of Vilnius, analyzed the chemical composition of Druskininkai's waters and showed that they contain large amounts of Calcium, Sodium, Potassium, Iodine, Bromine, Iron and Magnesium.

* Calcium sulfide ( CaS ), a chemical compound

* Calcium fluoride ( CaF < sub > 2 </ sub >), a chemical compound

* Calcium sulfide ( CaS ), a chemical compound

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 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 levels in livestock feed are supplemented with it, such as for poultry ( when ground up ).

Calcium causes synaptic vesicles filled with neurotransmitter molecules to fuse with the membrane, releasing their contents into the synaptic cleft.

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

Calcium carbonate is susceptible to even a weak acid solution because the crystals of calcium carbonate react with the acetic acid in the vinegar to form calcium acetate and carbon dioxide.

Calcium oxide, in the form of lime, was often used for this purpose, since it could react with the carbon dioxide and sulfur dioxide produced during roasting and smelting to keep them out of the working environment.

The skin is washed with water and lime ( Calcium hydroxide ), but not together.

Calcium phosphide is often used in naval flares, as in contact with water it liberates phosphine which self-ignites in contact with air ; it is often used together with calcium carbide which releases acetylene.

Calcium binds with available oxalate in the gastrointestinal tract, thereby preventing its absorption into the bloodstream, and reducing oxalate absorption decreases kidney stone risk in susceptible people.

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

* Chicken soup revisited: Calcium content of soup increases with duration of cooking

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.

At a breakage site in Rome, Testaccio, close to the Tiber, the fragments, later wetted with Calcium hydroxide ( Calce viva ), remained to create a hill now named Monte Testaccio, high and more than 1 km in circumference.

When the cement paste exposed to the air and meteoric water reacts with the atmospheric CO < sub > 2 </ sub >, portlandite and the Calcium Silicate Hydrate ( CSH ) of the hardened cement paste become progressively carbonated and the high pH gradually decreases from 13. 5 – 12. 5 to 8. 5, the pH of water in equilibrium with calcite ( calcium carbonate ) and the steel is no longer passivated.

Calcium channel blockers and losartan are associated with a lower risk of gout as compared to other medications for hypertension.

* Calcium, salt ( sodium and chloride ), magnesium, and potassium ( along with phosphorus and sulfur ) are sometimes added to the list of macronutrients because they are required in large quantities compared to other vitamins and minerals.