Natural pearls are believed to form as a result of an injury to the outer coat membrane, causing the cells to shift.

Just as humans have specialized cells for bone formation, some cells in the outer coat membrane of pearl shells are responsible for biomineralization, secreting calcium carbonate that makes up the shell and the pearl.

These displaced cells can form a "nacreous capsule," created by pearl-producing cells, which expands as the pearl grows. This process occurs when the mother-of-pearl is attacked by another organism. Contrary to the popular sand theory, sand is inert and would not actively invade the outer coat tissue. Natural pearls exclusively grow from the coat membrane, the only organ capable of secreting calcium carbonate and forming pearls without human intervention.

In the early 20th century, the technique of culturing round pearls was invented and refined over time. Mikimoto Kōkichi and his company further developed the original Mise-Nishikawa method, introducing round cultured pearls to the global market in 1919. To produce cultured pearls, three materials are necessary: a host shell, the outer mantle tissue of a donor shell, and a nucleus. Typically, the nucleus is crafted from Mississippi freshwater shells, also composed of calcium carbonate, cut and polished into a round shape.

Once implanted, peritoneal tissue slowly forms nacre around the spherical nucleus, a process taking approximately 30 days. The nacre is responsible for secreting and depositing a regular layer of perlage on the nucleus, ultimately forming the pearl. This method of culturing pearls with nucleated pearls has remained largely unchanged from its inception to the present day. For more information, refer to the video in the Sustainability of Pearl Cultivation section, demonstrating the process of cultivating saltwater nucleated pearls in French Polynesia.

There are two primary types of pearls: natural and cultured. Natural pearls occur spontaneously, while cultured pearls result from deliberate implantation of nuclei or cell transplantation and artificial culture.

Cultured pearls can be further categorized into nucleated and non-nucleated pearls. In nucleated pearls, small pieces of cells are transplanted simultaneously with the shell pearl nucleus, allowing the secreted perlage to be deposited on the nuclear surface, cultivating into a spherical pearl. Pearls formed solely by inoculating with celllets are known as non-nucleated pearls. Pearls are also classified based on the type of mother-of-pearl harvested, such as Honjo pearls, butterfly shell pearls, and triangular sail mussel pearls.

Pearls can be categorized according to the different parts of the mother-of-pearl formation, into free pearls and shell pearls. Shell pearls, attached to the shell, are hemispherical pearls characterized by their large size and lustrous appearance, albeit of inferior quality. In addition to their aesthetic appeal, pearls hold significant cultural and historical value. Throughout history, pearls have been revered as symbols of purity, wealth, and status in many societies. From ancient civilizations to modern times, pearls have adorned royalty, been featured in jewelry, and used as currency. The pearl trade has influenced economies and spurred exploration, leading to the discovery of new lands. Today, pearls continue to captivate and inspire, not only for their beauty but also for their enduring legacy as timeless treasures of the sea.