Here we are back again with this topic that I find increasingly interesting, due in part because I have used it as a form of catharsis, allowing me to remember one of the reasons why we started a Pearl Aquaculture project -some 17 years ago- when we were still students at the Guaymas Campus of the Tec de Monterrey. In those days, we first wanted to understand the reasons or logic surrounding the origin of natural pearls and how they are created within the pearl oysters and -of course- there was this previous “knowledge” about the origin of pearls: the mystical, magical, whimsical and musical “grain of sand theory“, which is really just another “pearl myth”.

Another Myth that Afflicts Humanity

It seems that regardless of the time period or place, this sand-grain-to-pearl myth has become very popular: it can be heard almost in any country and language. In my case my grandmother told me, when I was just a child, that pearls grew in an oyster as a result of an irritation caused by a grain of sand, so that there was no better choice for the little animal than to coat the painful and offensive particle with soft layers of nacre. I, of course, assimilated this important information and used it wherever there was an opportunity  –and there were not many I must admit- until it came time to put this theory to the test.

Previous Experiments

From Left to Right: Manue, Enrique & Douglas

Back in 1991, our select group of friends – including Mauricio Atl Tahuilan, Carlos Navarro Serment and Jesús Gutiérrez – had helped us to collect some 70 Pearl oysters to start off our studies on Pearl oyster reproduction and culture. Most of the oysters collected were “Black Lips” (Pinctada mazatlanica) and only a few specimens were “Rainbow Lips” (Pteria sterna), so we use some of these few animals for a very simple experiment: use sand to produce natural pearls. And the result was simply disappointing: we did not obtain a single Pearl. Zero. Zilch. Nothing. Nada. And there arose the question of why didn’t it work? Because we all know that a grain of sand will induce the production of a pearl…thus, a thousand grains of sand should be capable of allowing for the production of a thousand pearls and a million grains of sand …well, a million pearls!!! It was just so obvious and foolproof.

But it was not. As much sand as we used, we could not produce pearls. Not a single one. On the other hand, when we took a peek inside our oysters we noticed that the oysters were perfectly clean, without a trace of sand. We could not know -for real- what really happened in those days because we simply did not have the time to sit there -in front of an oyster- for some 24 straight hours. Can you imagine yourself sitting, just watching an animal that -for some people- is as interesting as a rock??? Therefore, we came up with conjectures and hypotheses, but we never quite knew what was truly happening; anyway, we were “satisfied” with our guesses. Many years have passed now since those days, and the technology to help us is now available –and is also inexpensive- to perform these small experiments…and, of course, for the “birth” of this Blog to have the motivation to write and document the experiments.

Experimenting with sand: the Present

We used a small fish tank with clean seawater to introduce two “Rainbow Lipped oysters” into which we had –previously- introduce one and a half tablespoons of sand. We placed a small video camera to take a time-lapse video for the next 18 hours to record what happens to an oyster which has sand inside. The results did not astonish us, and lived up to our expectations.

The Results

After 3 hours in the tank, oysters would quickly open and close their valves, in a movement and launched a “cloud” of sand out of their bodies. This action removed a great proportion of sand from their bodies, but for the next 8 hours the oysters continued to, slowly, releases small “sand packets”. These “sand packets” consist of a sticky mucus that the oyster secretes in order to “bind” or adhere the sand, and thus it is more easy for them to remove the annoying particles. By next morning, the oysters were almost perfectly clean.

While – at first view – the oysters seemed to be clean from sand (we could see the most of the sand laying at the bottom of the tank) an oyster was sacrificed in order to inspect its body thoroughly, and we still managed to find a very small amount of sand inside. Under natural conditions, the oyster would have managed to remove all remaining sand in some additional hours, but here it was necessary to see the “mucus in action”: our video displays how the Oyster uses its mucus to catch some sand particles and helps to eliminate them.


Pearl oysters are perfectly adapted to their natural environment – the ocean – which has an inexhaustible source of sand. Because of this perfect adaptation, these lowly creatures can – very easily – remove every single annoying grain of sand from their bodies; thus, we can discard sand as being able to help produce natural pearls. In my opinion this is highly unlikely.

Thus, we hope that with the information generated by this test and the proofs on video we will help –once and for all- eliminate the false myth of the “grain of sand”. We hope that this myth will not become resurrected –a zombie of its former self- and come back to haunt us in the future… I swear that if I have to listen –once more- the question of “Is it not a grain of sand that makes the pearl?” something very, very bad, will happen …. I’m just joking: I have already been seared in the flesh –and mind and soul- with this question for years and years, so I am certain I will be able to sustain it longer (but try not to put me to the test, please).

A Blister Pearl!

While inspecting the oyster that was sacrificed for the “grain of sand experiment” I found a worm-like mud-blister pearl. Since our last blog-episode was about these pearls, and I already had the camera rigged it was just natural to make this information available for you all. So, I simply used a scalpel to break the mother-of-pearl layer on this “small tunnel” and found a small orange colored worm. It was clearly a drill-worm (genus Polydora). This discovery can be seen in the video as well.

Coming soon

This Blog will continue to have more information of interest to you, but probably this information will become a little more “spaced” in time, since our farming activities become intensified during the winter season and we usually spend more time at the farm than at the office (where I write the Blog).

So please do not despair, I promise more posts in the near future and do continue to visit our Blog and send your comments and suggestions.