Pearls are produced from pearl mussels. When the mussel itself is stimulated by foreign bodies entering the mantle of the mussel, but it cannot be excluded, calcium carbonate and mother-of-pearl are secreted to cover it, about 3-4 times a day. The thickness of each covering is only 0.5 micron, and it takes 2-5 years to grow into gem-grade pearls.

Pearl is an ancient organic gem, a hard and smooth product produced by mollusks (mainly oysters). The calcium carbonate-containing mineral (aragonite) beads produced by endocrine function consist of a large number of tiny aragonite crystals.

The reason is that 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".

China is one of the earliest countries in the world to use pearls. As early as 4000 years ago, it was recorded that mussels could produce pearls in Shangshu Yugong, and the contents of pearls were also recorded in The Book of Songs, Classic of Mountains and Seas, Erya and Zhouyi. Pearls are divided into natural pearls and cultured pearls according to their causes. Natural pearls mainly refer to pearls naturally formed in shellfish and mussels.