Pearl is an ancient organic gem, which is produced in mollusks such as Pinctada and Pinctada. The calcium carbonate-containing mineral (aragonite) beads produced by endocrine function consist of a large number of tiny aragonite crystals. The chemical composition of pearl is: CaCO39 1.6%, H2O and organic matter are 4% and 0.4% respectively.

The principle of pearl formation:

1. Peripheral

The mantle of mussels is stimulated by the invasion of foreign bodies (sand and parasites). The epidermal cells in the stimulation area take foreign bodies as the core and fall into the connective tissue of the mantle. Some of the trapped epidermal cells divide themselves to form nacre, which secretes nacre and the nucleus is wrapped layer by layer to form pearl. Pearls with foreign bodies as the core are called "nucleated pearls".

2. Internal factors

After pathological stimulation, a part of the outer skin of the mantle undergoes cell division and separation, and then it is wrapped by organic substances secreted by itself and gradually falls into the connective tissue of the mantle, forming pearl sacs and pearls. Because there is no foreign body as the core, it is called "seedless pearl".

At present, cultured pearls are cut from the mantle of pearl-rearing mussels by artificial methods according to the above principles, and implanted into the connective tissue of the mantle together with the artificial nucleus prepared by mussel shells. The implanted cell fragments rapidly proliferate around the artificial nucleus according to the nutrition provided to the connective tissue, forming pearl sacs and secreting nacre, thus producing artificial nucleated pearls. Artificial seedless pearls are pearls produced by implanting only small pieces of cells into the mantle, forming pearl sacs through cell proliferation, and secreting mother-of-pearl into the sacs.