Calcium is the fifth most abundant element in the Earths crust. Calcium reactions can take place as calcium is a somewhat reactive metal. Harder then lead but generally considered to be a soft metal, it can be easily cut with a knife. It is a silvery metallic element that has to be extracted by electrolysis from a fused salt like calcium chloride. Once it is made it quickly forms a grey white oxide and nitrate coating as the calcium reactions take place with the air. Although calcium is not an easy element to burn, once it is set on fire it will burn with a bright, very intense red light.

Calcium reactions with water produce hydrogen gas at a rate that is fast enough to be observed. Although this calcium reaction happens fairly quickly, it does not typically generate a lot of heat. The calcium reactions with water happen at a very fast speed, when the calcium is in a powder form. This is due to the fact that there is an increased surface area, and the powder form speeds up the reaction with water. In a solid form the calcium reactions can take a much time to happen. This is due in part to the fact that it is protected by insoluble white calcium hydroxide. In cases where the water solutions of acids, where the salt is water soluble, the calcium reactions happen very quickly.

Calcium hydroxide is also known as slaked lime, slake lime, hydrogenated lime or pickling lime. It is a colorless crystal or white powder that is made when calcium oxide is combined, or slaked with water. It can also be preceded by mixing an aqueous solution of calcium chloride and an aqueous solution of sodium hydroxide. When this type of calcium reaction takes place the end result is a product called portandite. This natural production of portandite is by all accounts a rare mineral that can be found in some metamorphic, plutonic or volcanic rocks. Burning coal dumps is also known to cause this type of calcium reaction.

Another formation that is developed with calcium reactions is called calcium chloride. This is a common salt that acts like a typical ionic halide and is in a solid state when it is at room temperature. Some of the most common uses of calcium chloride are as brine for refrigeration plants, to manage ice and dust on roadways and also in concrete. Another common use for this type of calcium reaction is as a desiccant. A desiccant is a hygroscopic substance that has the ability to induce or sustains a high state of dryness.

Another of the calcium reactions is made in the forming of calcium carbonate. This is a chemical compound that is most commonly found in rock through out the world. It is also the primary component of shells of marine organisms, pearls, snails and eggshells. This compound is routinely used in medicinal applications as a calcium supplement or as an antacid. If high quantities are consumed then it can become hazardous.