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Created page with "== Introduction == Calcium is a chemical element with the symbol Ca and atomic number 20. It is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust. Calcium is also the fifth-most-abundant dissolved ion in seawater by both molarity and mass, after sodium, chloride, magnesium, and sulfate. Image:Detail-43747.jpg|thumb|center|Close-up of a piece of pure calcium.|class=onl..."
