If you've ever struggled to remove a splinter and watched over time as your skin pushed it out on its own, you know that the human body is good at keeping out foreign invaders. The oyster's body is, too. When an irritant, such as sand or a parasite, makes its way between the oyster's shell and its mantle (the organ that creates the shell), the oyster's body jumps into defense mode. The mantle starts to wall off the foreign object with nacre, the same substance used in the inner shell and what most would call "mother of pearl." This process creates a pearl that gets bigger as time goes on, and it stays within the oyster until the oyster dies or humans harvest the pearl. But not all pearls are the near-perfect spheres you see on necklaces; rather, the pearl takes the shape of whatever object it covers. And different breeds of oyster create different colors of pearls. That's why you'll find pearls in oval, teardrop, and "baroque" shapes, and colors ranging from bright white to pale pink to deep black.
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Key Facts In This Video
Oysters make pearls as a defensive response to foreign objects. 00:11
The mantle begins to deposit a substance called nacre, or mother of pearl, onto it. This is the same substance that makes up the inner shell, and any damage to the shell that reaches the mantle will also show the same response. 00:30
Pearl farmers usually use balls of ground, polished mussel shell to start the pearl making process. Using a similar substance to the pearl itself will prevent it from shattering when a hole is drilled into it. 02:27