Most gems are buried and could be found in rocks and mined in the ground. But there's one gem that is produced by a living organism. Yes, you're right. It's the pearl, the queen of all gems. Pearls are produced by mollusks such as oysters. This special characteristic of pearls sets it apart from all the other gems. Other mollusks such as clams and mussels can also produce pearls but it is a very rare occurrence unlike oysters. Most pearls, if not all, are produced by oysters in a saltwater or a freshwater environment. It can also be produced naturally or it could also be cultured. So do you want to know how oysters produce pearls? Then read on.
A pearl is basically a substance covered with layers and layers of nacre. Nacre is the material created by the mantle, while the mantle is the organ which produces the shell of the oyster using the minerals it gets from the food that the oyster eats. So the formation of pearl starts when an irritant, a foreign substance such as sand, dirt or whatever, enters the mantle. The mantle gets irritated and a reaction occurs which covers the irritant with layers and layers of nacre. This process eventually forms a pearl.
Pearls can be produced in two ways. It can be produced naturally and it can also be cultured. Cultured pearls share the same process of pearl formation as the natural ones. Their only difference is that there's no human intervention involved in the natural production of pearls. It's all the works of Mother Nature. And there you have it. That is how pearls are produced.