Calcium

In nature, calcium is found in the Earth's crust, 3.64 %, sea water, 400 g/ton, and items of biological origin like bone, teeth and shells [7]. The primary commercial source is limestone [7]. The isotopes found in nature are ⁴⁰Ca (97 %, stable), ⁴²Ca (0.64 %, stable), ⁴³Ca (0.145 %, stable), ⁴⁴Ca (2.06 %, stable), ⁴⁶Ca (0.003 %, stable) and ⁴⁸Ca (0.18 %, stable) [7].

In pure solid form, calcium exist in a face-centered cubic structure at < 300 °C [7]