How Does a Pearl Come Into Existence?

A pearl comes into existence when a mollusk produces a substance called nacre to protect itself from an irritant. The mollusk continues to add layer after layer of nacre until the irritant is completely sealed off. The iridescent finish of a pearl is created when light reflects off of the different layers of nacre at different angles.

Diamonds and jewels may be a girl’s best friend, and everything from rocks from the ground to organic byproducts from the ocean make it into jewelry for the fairer sex. Shiny pearls, for example, are often linked together in a necklace and large gemstones from deep in the earth are often the main feature of wedding rings. It’s true that gems make our lives a bit more shiny, but one question has always intrigued me about one particular “stone” that people seem to love.

Have you ever wondered how a pearl forms? Well, if you’re like me, then you have. The story of how a pearl forms is as shiny and special as the stone itself.

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Mollusks: The Pearl Parents



Mollusks (or molluscs) are a class within a large phylum of invertebrate animals known as Mollusca. There are around 85,000 species of mollusks that we have recognized thus far. They are the largest marine phylum, which is evidenced by the fact that they make up 20% of all aquatic organisms. They can be found in both freshwater and terrestrial habitats. Some of the most commonly known mollusks include oysters, mussels and clams, but there are so many more!

Inside these creatures, if we’re lucky, we might just find our pearls!


How does it Work?

Pearls are formed inside the bodies of mollusks, such as oysters, clams and mussels. When an external particle (called an ‘irritant’), such as a grain of sand or a bit of floating food, enters the body of these organisms, the process of pearl formation begins. As expected, when the organism senses that an irritant has entered its shell and irritated the soft tissues of its body, it initially tries to expel it. If that doesn’t work out, however, it launches a unique defense mechanism to protect itself from the intruder.

formation of a pearl

In order to make sure that the irritant doesn’t harm or contaminate the shell’s tissues any further, the oyster produces a substance called nacre (also called mother of pearl, for obvious reasons), which is also present on the inner lining of the body of the oyster. The mollusk continues adding layer after layer to guarantee that the intruder is sealed inside and is unable to harm the mollusk any further. After a certain number of nacre layers have formed, the irritant is completely blocked off from the tissues and voila! You have a gem!

Cultured pearls are made in more or less the same way; the only major difference is that in cultured pearls, the intruder (a grain) is carefully embedded inside the mollusk in a deliberate effort to stimulate pearl formation.

Internal Reflection

When light strikes the surface of a pearl, some of it is reflected, while some is absorbed. When the light rays enter the pearl, they are reflected at many different angles. These reflections interfere with each other at different wavelengths, which scatters various colors in different directions, thereby imparting the iridescent finish to pearls that we see.


Credits:Africa Studio/Shutterstock

Many people say that one man’s trash is another man’s treasure, and that is certainly true for pearls, which start off as an unwanted irritant and become one of the most desired things in the world. A treasure indeed!

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About the Author

Ashish is a Science graduate (Bachelor of Science) from Punjabi University (India). He spearheads the content and editorial wing of ScienceABC and manages its official Youtube channel. He’s a Harry Potter fan and tries, in vain, to use spells and charms (Accio! [insert object name]) in real life to get things done. He totally gets why JRR Tolkien would create, from scratch, a language spoken by elves, and tries to bring the same passion in everything he does. A big admirer of Richard Feynman and Nikola Tesla, he obsesses over how thoroughly science dictates every aspect of life… in this universe, at least.

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