what form does calcium occur in naturally
Calcium occurs in water naturally. Seawater contains approximately 400 ppm calcium. One of the main reasons for the abundance of calcium in water is its natural occurrence in the earth's crust.
Calcium carbonate is a common, naturally occurring calcium salt that is often used as a source of calcium in supplements. Its abundance in nature makes calcium carbonate the least expensive supplemental calcium salt. It is also a major component of some types of stone that are used in architecture and sculpture.