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
Coral calcium Coral calcium Coral calcium is a salt of calcium derived from fossilized coral reefs (primarily from limestone and coastal deposits). It has been promoted as an alternative, but unsubstantiated, treatment or cure for a number of health conditions. Coral calcium has been promoted as an alternative treatment or cure for a number of health conditions, often as part of an alkaline diet, by Robert Barefoot and others; Barefoot coauthored a book called "The Calcium Factor," and marketed coral calcium supplements with infomercials. According to a "Time" magazine article about Barefoot by Leon Jaroff, "The monthly cost of the recommended dose