Calcium nitrate are inorganic compounds with the formula Ca(NO3)2(H2O)x. The anhydrous compound, which is rarely encountered, absorbs moisture from the air to give the tetrahydrate. Both anhydrous and hydrated forms are colourless salts. Hydrated calcium nitrate, also called Norgessalpeter (Norwegian salpeter), is mainly used as a component in fertilizers, but it has other applications. Nitrocalcite is the name for a mineral which is a hydrated calcium nitrate that forms as an efflorescence where manure contacts concrete or limestone in a dry environment as in stables or caverns. A variety of related salts are known including calcium ammonium nitrate decahydrate and calcium potassium nitrate decahydrate.[3] Production and reactivity Norgessalpeter was synthesized at Notodden, Norway in 1905 by the Birkeland–Eyde process. Most of the world's calcium nitrate is now made in Porsgrunn. It is produced by treating limestone with nitric acid, followed by neutralization with ammonia: CaCO3 + 2 HNO3 → Ca(NO3)2 + CO2 + H2O It is also an intermediate product of the Odda Process: Ca5(PO4)3OH + 10 HNO3 → 3 H3PO4 + 5 Ca(NO3)2 + H2O It can also be prepared from an aqueous solution of ammonium nitrate, and calcium hydroxide: 2 NH4NO3 + Ca(OH)2 → Ca(NO3)2 + 2 NH4OH Like related alkaline earth metal nitrates, calcium nitrate decomposes upon heating (starting at 500 °C) to release nitrogen dioxide:[3] 2 Ca(NO3)2 → 2 CaO + 4 NO2 + O2 ΔH = 369 kJ/mol Applications Use in agriculture The fertilizer grade (15.5-0-0 + 19% Ca) is popular in the greenhouse and hydroponics trades; it contains ammonium nitrate and water, as the "double salt" 5Ca(NO3)2·NH4NO3·10H2O. This is called calcium ammonium nitrate and often the name calcium nitrate prill is used as it always comes in a prilled (granular) form. Formulations lacking ammonia are also known: Ca(NO3)2·4H2O (11.9-0-0 + 16.9 Ca) and the water-free 17-0-0 + 23.6 Ca. A liquid formulation (9-0-0 + 11 Ca) is also offered. An anhydrous, air-stable derivative is the urea complex Ca(NO3)2·4[OC(NH2)2], which has been sold as Cal-Urea. Calcium nitrate is also used to control certain plant diseases. For example, dilute calcium nitrate (and calcium chloride) sprays are used to control bitter pit and cork spot in apple trees.[4]