Oysters make pearls as a natural defense mechanism against irritants such as grains of sand, parasites, or other foreign objects that enter their shells and come between the oyster’s mantle and shell. When this happens, the oyster’s mantle tissue secretes a substance called nacre (also known as mother-of-pearl), which is composed of layers of aragonite (a form of calcium carbonate) and conchiolin (a protein that acts as a binding agent). The oyster coats the irritant with multiple layers of nacre, gradually building up a pearl over time
. The process involves the following steps:
- An irritant enters the oyster’s shell and lodges between the mantle and shell.
- The oyster’s outer mantle epithelium forms a pearl sac around the irritant.
- Epithelial cells of the pearl sac secrete nacre layers, which consist of alternating layers of aragonite crystals and conchiolin.
- These layers accumulate concentrically, smoothing out irregularities and eventually forming the smooth, lustrous pearl.
- This layering process can take months or even years, depending on the oyster species and pearl size
In cultured pearl production, humans manually insert a nucleus (often a bead) and a piece of mantle tissue into the oyster to stimulate nacre secretion and pearl formation, mimicking the natural process
. In summary, an oyster produces a pearl by isolating an irritant with layers of nacre secreted by its mantle tissue, creating the beautiful gem known as a pearl
