Calcium strontium or barium, the oxide–nitride coating that results in air is stable and lathe machining and other standard metallurgical techniques are suitable for calcium. In the United States and Canada, calcium is instead produced by reducing lime with aluminium at high temperatures. Calcium provides a link between tectonics, climate, and the carbon cycle. In the simplest terms, uplift of mountains exposes calcium-bearing rocks to chemical weathering and releases Ca into surface water. These ions are transported to the ocean where they react with dissolved CO to form limestone (), which in turn settles to the sea floor where it is
Calcium citrate Calcium citrate Calcium citrate is the calcium salt of citric acid. It is commonly used as a food additive (E333), usually as a preservative, but sometimes for flavor. In this sense, it is similar to sodium citrate. Calcium citrate is also found in some dietary calcium supplements (e.g. Citracal). Calcium makes up 24.1% of calcium citrate (anhydrous) and 21.1% of calcium citrate (tetrahydrate) by mass. The tetrahydrate occurs in nature as the mineral Earlandite. Calcium citrate is sparingly soluble in water. Needle-shaped crystals of tricalcium dicitrate tetrahydrate [Ca(CHO)(HO)]·2HO were obtained by hydrothermal synthesis. The crystal structure comprises a three-dimensional network