Together, they make the substance, calcium phosphate. Sidewalk chalk is made from calcium and sulfate, which makes calcium sulfate. One of the most common chemicals connected to calcium is called ...

Corals are colonial organisms made up of individual polyps ... polyps secrete a calcium carbonate skeleton, and it is this skeleton that becomes the foundation of coral reef ecosystems.

These marine invertebrate animals have hard exoskeletons made of calcium carbonate, and are sessile, meaning permanently fixed in one place. Polyps grow slowly, forming different shapes and sizes ...