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
The Lost Symbol as the commands of an all-powerful deity. This interpretation has been lost amid centuries of scientific skepticism and fundamentalist zealotry. The Masons have (metaphorically) buried it, believing that, when the time is right, its rediscovery will usher in a new era of human enlightenment. "The Lost Symbol" had been in development for several years; originally expected in 2006, the projected publication date was pushed back multiple times. When officially announced, the hardcopy book was on pre-order lists for months leading up to its release, being heavily ordered both in the United States and Canada. The book was published on September