Coral is a kind of marine cylindrical coelenterate, which is automatically fixed on the calcareous remains of ancestral corals in the white larval stage. Coral is the shell secreted by coral. The chemical composition of coral is mainly CaCO3, which exists in the form of microcrystalline calcite aggregate, and there is a certain amount of organic matter in the composition, which is mostly dendritic and has vertical stripes.

Each single coral has concentric circles and radial stripes on the cross section, and the color is often white, but there are also a little blue and black. Coral is not only like branches, but also bright and beautiful in color, which can be used as decorations and has high medicinal value.