What is a Non-Nacreous Pearl?
Quite a word, isn't it? Non-Nacreous! Well, let's take it back to the word nacre. Does that sound a little friendlier? Pronounced with a long "a," nacre is mother of pearl. It is the building block for a pearl. Nacre is that beautiful, lustrous material in the inside of a shell. And when a mollusk is invaded by a predator or when an irritant gets in its soft tissue body, the mollusk uses its nacre to produce a pearl! Lovely!
The Big Defense
Pearls, as you know, are defense mechanisms created by mollusks to protect against their little invaders.. bacteria, small aquatic organisms, maybe a bit of shell or something. When a natural pearl is formed, this little invasion happens naturally. So, a bad guy gets in the soft tissue of a mollusk and the mollusk protects itself by covering that little invader up with the same material it uses to make its shell. Nacre! In the case of cultured pearls, this invasion is manufactured. An irritant is inserted in the mollusk to create the irritation and spur the mollusk to create a cultured pearl. Fun fact, this is the difference in natural and culture pearls!
Beautiful ... or Not?
The result of this little invasion is a beautiful pearl and sometimes the result is a not so beautiful pearl. Truthfully, when you are dealing with natural pearls, you kind of never know what you will get. But, what happens, lets say, when you are eating that plate of oysters and you find some funky chalky looking thing? It is a pearl, for sure, but it almost looks more like a tooth rather than a gem fit for queens. This, my dear friends, is a non-nacreous pearl!
Did you see the article about the woman who found a "pearl necklace" in her fried oyster? She found 51 pearls in one oyster and they kind of look like tiny teeth on a plate. They are dense, porcelain-looking bits.
And take a look at this yummy feast....
More About Calcium Carbonate[caption id="attachment_8470" align="alignleft" width="300"] A HUGE non-nacreous pearl from a giant clam.[/caption]
So, what is a non-nacreous pearl? First, let's talk about a mollusk shell! Shells are made of calcium carbonate. Calcium carbonate is formed by carbon, oxygen and calcium. It is a building block for a whole lot of things... shells, eggshells, pearls and it is found in lots of rocks too.
This calcium carbonate has two distinct, naturally occurring, crystal forms. These are calcite and aragonite and they are comprised of the same material but with a different crystalline structure.
Aragonite versus Calcite
The aragonite tends to be prettier because aragonite usually has a more orderly crystal structure. This means, the light reflects well through the crystalline layers. Aragonite is really the good stuff. It is the gorgeous nacre, the mother-of-pearl, and the beauty we typically imagine when we think of pearls.
Calcite, on the other hand, is the exact same substance but with a different structure. If you could see it under a microscope, the crystal structure would not appear to be uniform. Because of its structure, it does not reflect and refract light like aragonite. So the beauty does not shine through the layers.
When I first wrote this post I said that non-nacreous pearls are not as shiny as nacreous pearls. That is sort of true and kind of not true, either. They don't show off like the aragonite pearls we think of but they still can have a polished shine. Non-nacreous is denser, more like a thick porcelain. Pretty in its on way but, not the same!
This calcite is what makes a non-nacreous pearl! Some pearls can have a mix of aragonite and calcite but if the light does not reflect through that structure giving you a nice, bright, lustrous pearl, it is still considered a non-nacreous pearl.
Brittany commented on The Pearl Girls Facebook page, "It's odd that we consider the Pearl a gem stone made from a living creature but gallstones and kidney stones aren't considered lol. Maybe If we polish them up they could be beautiful and valuable... Then again...maybe not😋"
Well, Brittany, here is the crazy thing: that is exactly what these non-nacreous pearls are. They are a calcium deposit from the mollusk. They do not form the same way that nacreous pearls form, as a protective mechanism. These are concretions. Which is a fancy way of saying something hardened like concrete. in this case, calcium hardened within the body of the mollusk.
Giant Clam[caption id="attachment_8469" align="alignleft" width="300"] Thanks for the image Creature Teacher![/caption]
Some of the largest pearls in the world come from the giant clam in The Philippines. This giant clam creates one giant pearl and the pearl is thick and dense and white. It does not reflect beautiful layers of light and color. It is pretty mono-chromatic, actually. This is what we mean by a non-nacreous pearl. It is still made of calcium carbonate but it lacks the beautiful nacre pearls are known for.
Even conch pearls, although beautiful in color, lack the depth of pearlescent beauty that pearls usually possess. Instead, conch pearls have a porcelain like shine.
UPDATE: Pearls from Canada?
On March 28, 2019 the CBC in Canada posted an article about what could be the biggest pearl in the world. A 27 kilogram pearl that originated from a giant clam. Abraham Reyes decided to share this pearl with the world. His family received it in 1959.
His grandfather gave a giant clam to his aunt when he came to Manila to visit her. The grandfather had bought the clam from a fisherman in Camiguin, a small island southeast of Manila. And what was inside? A pearl! This big non-nacreous pearl was in the clam and the grandfather had no idea!
Reyes says "These giant clams were very common. They were used for baptismal baths. Some of them are even in gardens… some of them had abnormalities that they didn't know were pearls."
Unfortunately, these giant clams were over-fished and over-harvested. Environmentalists have proposed listing seven of the ten species of giant clams under the United States Endangered Species Act.