How does oyster make natural pearls?
When a foreign substance slips into the oyster between the mantle and the shell, it irritates the mantle. It's kind of like the oyster getting a splinter. The oyster's natural reaction to protect itself is to cover up that irritant. The mantle covers the irritant with layers of the same substance that is used to create the shell. This eventually forms a pearl. Most of the pearls are nicely rounded and are the most valuable ones. Some pearls are irregular in shape.
Pearls can also be cultured by cutting a small slit in the mantle tissue and inserting some small inrritant to induce the production of pearls. Cultured pearls are not as expensive a natural pearls.
