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How Do Oysters Make Pearls?

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Layer upon layer of nacre, also known as mother-of-pearl, coat a grain of sand until the iridescent gem is formed. (Image credit: Photowitch | Dreamstime.com)

A natural pearl begins its life inside an oyster's shell when an intruder, such as a grain of sand or bit of floating food, slips in between one of the two shells of the oyster, a type of mollusk, and the protective layer that covers the mollusk's organs, called the mantle.

In order to protect itself from irritation, the oyster will quickly begin covering the uninvited visitor with layers of nacre — the mineral substance that fashions the mollusk's shells. Layer upon layer of nacre, also known as mother-of-pearl, coat the grain of sand until the iridescent gem is formed.

Cultured pearls are made in the same way. The only difference is that instead of accidental circumstances, a "pearl farmer" embeds a grain of sand into the mollusk.

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Michelle Bryner
Michelle writes about technology and chemistry for Live Science. She has a Bachelor of Science in Chemistry from the Salisbury University, a Bachelor of Chemical Engineering from the University of Delaware and a degree in Science Journalism from New York University. She is an active Muay Thai kickboxer at Five Points Academy and loves exploring NYC with friends.