For centuries, lime was used to make plaster and mortar by heating limestone. As it seemed impossible to reduce it further, Antoine Lavoisier classified it as an ‘earth’. However, he suspected that it was an oxide of an unknown element. Later in 1808, it was reduced to moist lime by electrolysis by Humphry Davy but his method was in vain. Hence, he produced an amalgam of Calcium and mercury with a mixture of lime and mercury oxide. What he obtained out of it was not satisfactory though. He added more lime to the mixture and distilled off the mercury, leaving just Calcium behind.

Being the fifth most abundant element of the earth’s crust, Calcium forms about 3% of it. Calcium forms an essential part of leaves, bones, teeth and shells. Never found isolated, it is combined in minerals such as limestone, gypsum and fluorite. It is prepared by the electrolysis of fused chloride and Calcium fluoride as it lowers the melting point. 

Some of the important characteristics of Calcium include:

• Calcium is one of the alkaline earth metals, silver in colour and is rather hard.
• It reacts with water and burns with a yellow–red flame and readily forms a white coating of nitride in air.
• Its large number of both natural and manufactured compounds is widely used.
• It is highly soluble in water that contains carbon dioxide and is an important component of stalactites and stalagmites.
• Calcium hardens water.
• Calcium has the lightest density of the alkaline earth metals of about 1.55g/cm³.

There are about five stable isotopes of Calcium, namely ⁴⁰Ca, ⁴²Ca, ⁴³Ca, ⁴⁴Ca and ⁴⁶Ca. Also, isotope ⁴⁸Ca may also be considered stable as it has such a long half–life and can be used for all practical purposes. ⁴⁰Ca forms about 97% of the naturally occurring form and is one of the daughter products of ⁴⁰K decay and ⁴⁰Ar. It has a nucleus of 20 protons and 20 neutrons that make it the heaviest stable isotope of any element and its prevalence in K–Ar dating have hindered its use. Calcium is formed from the reaction of carbon with various numbers of alpha particles in supernova explosions and continues until the most common Calcium isotope has been synthesized. 

As discussed earlier, Calcium constitutes an important nutrient for building strong bones. Hence, foods rich in Calcium include milk, yogurt, cheese, dark green vegetables and pudding. In addition to these, beverages of soy and tofu are Calcium fortified. 

Some of the common and important uses of Calcium are:

• Calcium phosphate helps the animal skeletons get their rigidity and is essential for human nutrition.
• It is necessary for plant growth and the eggs of the birds and shells are made of Calcium carbonate.
• When preparing metals from their halogen and oxygen compounds, Calcium is used as a reducing agent and as a reagent in the purification of the inert gases.
• It helps to fix atmospheric nitrogen and acts as a scavenger and decarbonizer in metallurgy for making alloys.
• Other common uses of Calcium include making of lime, bricks, cement, glass, paint, paper, sugar, glazes and many other uses.

One of the main causes of lack of Calcium is Osteoporosis. It is a disease in which bones become extremely porous and are subject to fracture. Causes of high blood calcium levels include bone cancer, overactive thyroid gland or hyperthyroidism and overactive parathyroid or hyperparathyroidism. This high blood calcium levels in the body may lead to kidney stones or nephrolithiasis and milk–alkali syndrome. It can also disrupt the absorption of iron, zinc, magnesium and phosphorous.