The Shape of Pearls

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Star and Moon Pearl Necklaces by The Pearl GirlsWith the launch of this week’s Star and Moon Necklace, I decided to write a blog post discussing the shape of pearls and why pearls have the shapes that they do! Is it possible (gasp!) that I have never written a comprehensive blog post on the Shape of Pearls?

Read more about Coin Pearls here! And, I even wrote about Star Shaped Pearls here. However, I cannot find a Shape of Pearls article in all of these 500+ posts of mine. So, here goes!

In the Beginning

mother of pearl - inside mother of pearl shell - The Pearl Girls

Let’s start at the beginning. I know most of you know the ins and outs of natural and cultured pearl production but, as an overview, here goes! A pearl is formed by a mollusk. Any mollusk that can make its own shell can make a pearl. This means mussels, oysters, clams and more can make a pearl. Why? Because these organisms use their same shell making material to make a pearl! This is why that beautiful stuff on the inside of a shell is called mother-of-pearl. It is the same beautiful nacre that the organism uses to make a pearl!

So, why do mollusks make pearls that look the way they do? Great question! But first…

Why do mollusks make pearls?

peal sac with pearl inside

Pearls are a line of defense. Let’s say a mussel is living the good life, living in a river sucking water in and out (they filter water to absorb nutrients for their food!) and suddenly something gets in their soft tissue body. Although some people think it is sand that forms a pearl, that is not true. It is usually something that packs a bigger punch. A piece of shell, an organism… something that gets in the mollusks body and can’t get out. What happens to the mussel? Well, it might die! As with any living creature, an injury or invasion may kill it. If it survives, it will essentially neutralize the threat. It does this by creating a little protective sac around the invasion and then secreting the same material it uses to make its shell onto the organism or material that invaded it. This becomes a pearl. Over time, the organism secretes more and more nacre and shapes this invasion and a pearl is formed. See it here inside its sac?

Why are pearls shaped the way they are?

We finally made it! The real question with the shape of pearls is… why are they shaped the way they are? I have boiled this down to three reasons: The inside, the outside and the organism!

It’s What’s Inside!

snail shell
This image is from

Let’s start with the inside! The original invader forms the nucleus of the pearl. When pearls form naturally, this nucleus can be almost anything… a shell, maybe a rock, another organism. Who knows! I have drilled through a few natural pearls and ended up with a smoking drill and and a burning question … “What is in there?!” Pearl divers have told me they have found pearls in the shape of a snail! Hmm… could there be a snail shell inside that pearl?


The Shape of Pearls - Mother of Pearl Beads



In many cultured pearl productions, a round mother of pearl bead is inserted into the mollusk and it starts the pearl making process. So guess what shape that pearl is most likely to take? A round shape!

And freshwater pearls, those we typically associate with being a variety of unique shapes? They only have a soft tissue nucleus so they are free to make a variety of shapes!

No matter what is inside, it serves as a template of sorts for the pearl formation. So, if a round bead is the nucleus, it is more likely that the pearl will be round. If a star shaped mother of pearl bead is inserted in the mollusk, well here comes something that looks like a star shaped pearl. Round disks are inserted to form coin pearls. So, the number one indicator of pearl shape is what is inside of that pearl.

Number two is what is on the outside!


Where was that pearl formed?

The Shape of Pearls - American Pearls - The Pearl GirlsNatural American pearls come in two primary shapes, a nugget shape forms in the soft tissue body and pearl “teeth” (dagger like pearls) form near the hinge of the pearl. The pearl formation here is determined by the space the pearl has to form and the area where it forms. So, the second aspect of the shape of pearls is the “where” of the pearl. And that can influence the shape!


Baroque Pearl NecklaceWhen the Chinese wanted to form larger baroque pearls, they inserted a bead nucleus near the foot of the mollusk. That way, the pearl could grow big (there was more room!) and the organism could not expel the nucleus!


What Formed the Pearl?Tahitian Twist Earrings - the pearl girls

Finally, the actual organism can influence the shape of the pearl. Lets say a pearl was formed in the gonad of the oyster, this is very common in saltwater pearl production. And the gonad is a strong muscle. Sometimes, though, it is not uniformly strong. Think of someone who is strong in one area of their bodies and weak in another. It kind of reminds me of my left shoulder. Ever since I tore my rotator cuff in a snowboarding accident, I have not been as strong on the left side of my body. So, even my left bicep is not as strong as my right. The same is true in oysters. Their muscle may be not be uniform in strength. So, one part of the muscle may put more pressure on the pearl than the other part, thus creating a circled or drop shape as the pearl is forming. Have you ever Tahitian black pearlsheard of circled pearls? These are pearls that have rings around them. And these pearls formed in this shape because of the organism who formed them. So the organism affected the shape of the pearl.

Keep Them Healthy!

The health of the mollusk is huge! It is known in the pearl world that healthy mollusks and healthy waters form more beautiful pearls. Well, an unhealthy mollusk may produce a smaller pearl or may affect the overall health of the pearl. It is hard to create and secrete the very best mother of pearl when the health of the mollusk is affected!

What Does a Mollusk Do with its Pearl?Star and Moon Pearl Necklace by The Pearl Girls

In natural pearl production, the next best step (for the mollusk) is to eject the pearl from its soft body. This way the threat is both neutralized and eliminated. Sometimes, though, the mollusk can’t get rid of its pearl, and it just keeps it. And, in cultured pearl production, this is the goal! Pearl farmers do not want the mollusk to get rid of their pearl until it is harvested.

Then all those beautiful pearl shapes can become beautiful pieces of jewelry! See the new Star and Moon Pearl Necklace HERE!



2 thoughts on “The Shape of Pearls

  1. Dear India,

    Thank you for your “Shape Of Pearls” article. It is a treasure and one to keep for all time.
    As in anything, the more education on a subject the more interest is created for that subject.
    Happy New Year!

    Valerie Coffin

    1. Thanks Valerie!!! 🤗

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