Calcium CH ligand with the bulkier C(CH) ligand on the other hand increases the compound's solubility, volatility, and kinetic stability. Natural calcium is a mixture of five stable isotopes (Ca, Ca, Ca, Ca, and Ca) and one isotope with a half-life so long that it can be considered stable for all practical purposes (Ca, with a half-life of about 4.3 × 10 years). Calcium is the first (lightest) element to have six naturally occurring isotopes. By far the most common isotope of calcium in nature is Ca, which makes up 96.941% of all natural calcium. It is produced in the silicon-burning
Calcium carbonate Calcium carbonate shares the typical properties of other carbonates. Notably, Calcium carbonate will react with water that is saturated with carbon dioxide to form the soluble calcium bicarbonate. This reaction is important in the erosion of carbonate rock, forming caverns, and leads to hard water in many regions. An unusual form of calcium carbonate is the hexahydrate, ikaite, CaCO·6HO. Ikaite is stable only below 8 °C. The vast majority of calcium carbonate used in industry is extracted by mining or quarrying. Pure calcium carbonate (e.g. for food or pharmaceutical use), can be produced from a pure quarried source (usually marble).