Calcium

Calcium is a chemical element with symbol Ca and atomic number 20. Calcium is a soft gray alkaline earth metal, fifth-most-abundant element by mass in the Earth's crust. The ion Ca²⁺ is also the fifth-most-abundant dissolved ion in seawater by both molarity and mass, after sodium, chloride, magnesium, and sulfate.^[4] Free calcium metal is too reactive to occur in nature. Calcium is produced in supernova nucleosynthesis.

Calcium is essential for living organisms, in particular in cell physiology, where movement of the calcium ion into and out of the cytoplasm functions as a signal for many cellular processes. As a major material used in mineralization of bone, teeth and shells, calcium is the most abundant metal by mass in many animals.

Contents

  [hide] 

• 1Notable characteristics
  • 1.1H and K lines
• 2Compounds
• 3Isotopes
  • 3.1Isotope fractionation
• 4Geochemical cycling
• 5History
• 6Occurrence
• 7Applications
  • 7.1Calcium compounds
• 8Nutrition
  • 8.1Dietary supplements
  • 8.2Bone health
  • 8.3Cardiovascular impact
  • 8.4Cancer
• 9Cell signaling
• 10Hazards and toxicity
• 11See also
• 12References
• 13Further reading
• 14External links