Calcium Calcium Calcium is a chemical element with symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to its heavier homologues strontium and barium. It is the fifth most abundant element in Earth's crust and the third most abundant metal, after iron and aluminium. The most common calcium compound on Earth is calcium carbonate, found in limestone and the fossilised remnants of early sea life; gypsum, anhydrite, fluorite, and apatite are also sources of calcium. The
Calcium nitrate nitrate tetrahydrate is highly endothermic (cooling). For this reason, calcium nitrate tetrahydrate is sometimes used for regenerable cold packs. Calcium nitrate can be used as a part of molten salt mixtures. Typical are binary mixtures of calcium nitrate and potassium nitrate or ternary mixtures including also sodium nitrate. Those molten salts can be used to replace thermo oil in concentrated solar power plants for the heat transfer, but mostly those are used in heat storage. Calcium nitrate Calcium nitrate, also called "Norgessalpeter" (Norwegian saltpeter), is an inorganic compound with the formula Ca(NO). This colourless salt absorbs moisture from the air