Who says pearls are caused by grains of sand?


Well-known member
Jan 29, 2007
Available in PDF format on Google Books is the following classic:

Japanese Culture Pearls
A Successful Case of Science Applied in Aid of Nature
K. Mikimoto, 1907​

Page 4:

?Now it often happens that foreign substances such as sand grains,
microscopic organisms of various kinds, parasitic worms, crabs, or sometimes
even small fishes become introduced by accident or otherwise inside the
shell or into the tissues of the mollusc?s soft body.?

In any case, it's an historic volume for the electronic library.
Scientists Debunk Myth that Pearls come from "Grains of Sand"

Scientists Debunk Myth that Pearls come from "Grains of Sand"

“Now it often happens that foreign substances such as sand grains, microscopic organisms of various kinds, parasitic worms, crabs. or sometimes even small fishes become introduced by accident or otherwise inside the
shell or into the tissues of the mollusc’s soft body.”

Worms and sand are implicated in blisters. Urchins and pea crabs in free pearls. I have a snail mounted on a pendant.

Fish I've yet to see.


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The crab is so cool.

I took some liberty reconstructing it for visual effect, but the conjunctions surrounded the carapace in separate pearl sacs within a single mass.

The Olympia oyster has a parasite blister in the adductor scar and a conjoined pearl at the gonad.
Well Buck Nacre just doesn't have a chance of getting the true word out. (see the pearl professor's blog, Buck Nacre's article) It is a hoot, esp if you read the comments too.http://www.pearl-professor.com/2010/12/not-irritating.html

If Mikimoto said it, it must be true, so the grain of sand theory wins, yet again. (For newbies: the grain of sand belief doesn't have a grain of truth in it :D)
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Fish I've yet to see.

I have seen a pic of a nacre-coated fish in a shell- in Strack, maybe?

For Newbies: Far more likely, according to Strack's scholarship sources, the pearl sac is formed by an attack from a fish, in the mantle area or from something piercing the delicate mantle. The likelihood of this happening is very small, so there aren't many pearls happening in wild oysters and never have been.
Yes, I saw the fish picture also, but can't remember where it was. Guess we can cut Mikimoto some slack, at least he included the other options besides sand grains, and it was before 1907. Still, I find it annoying that someone with the reputation of author Richard W. Wise is repeating it.

As I was reading Secrets of the Gem Trade by Richard W Wise, Copywrite 2006, paperback version, these two separate entries:

"Pearl making is an irritating proposition for the pearl oyster. In nature, the pearl nucleus-a grain of sand or small bit of coral-works its way into the soft mantle tissues of the oyster causing irritation. To combat the discomfort, the oyster secrets nacre." page 141 This, in a section discussing the nucleation process of Tahitian pearls!

Again, page 142-143, "There are two basic types of pearls, natural and cultured. In either case the method of producing the pearl is essentially the same. An irritant in the form of a grain of sand, a piece of coral, or a (sic) implant introduced by man, is placed or finds its way into the soft mantle tissues of the host mollusk."

Dave, Thanks for the wonderfully educational photos.
EVEN STACK mentions the grain of sand!!!!!
She mentions a fish attack on page 116 that reaches the
"space between the mantle and shell where it can cause additional damage to the mantle tissue. Moreover, the path is now free for further intruders like small snails, crabs and other animal and vegetal parts of plankton, also for fish scales, broken parts of the shell, lumps of conchioline, small stones and the so frequently mentioned small grains of sand.
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I am reading up on that terminology when I came across this This is from a United Nations report. It seems to be from ca 1986
11.1 Natural pearl formation

The principal causative factor in pearl formation in a pearl oyster is the presence of a nucleus. It can be of organic or inorganic origin, such as parasites adults or larvae, molluscan eggs, decaying parts of plants, sand grains, epithelium or blood cells of the same animal, etc. These tiny particles or organisms enter the oyster when the shell valves are open for feeding and respiration. These foreign bodies may become embedded between the shell and mantle. In response to this stimulus, the foreign body is invaginated by the outer epithelium of the mantle and a pearl-sac is formed around it (Fig. 7 A).
Pearls are not produced without the formation of the pearl-sac. The pearl-sac is derived from the internal or external layer of the epithelium of the mantle or of the gill plates. The epithelial cells of the pearl-sac secrets the nacre which becomes deposited over the foreign body, forming a pearl in due course of time. These pearls are produced either within the mantle, in other soft tissues of the oyster, or between the mantle, and the interior surface of the shell. Such pearl production is accidental and occurs very rarely. They are generally small and irregular. Large and spherical pearls are still rarer to find. When the extraneous matter becomes fixed to the shell, only the exposed portion becomes covered by the pearl-sac resulting in a blister pearl.
Frankly, I am at a loss. So far, we have Mikomoto, Wise, Strack and these people, all including sand as a causative agent. Douglas (whom I trust more than any of these other sources), stands alone in disputing it and providing a little experiment to prove it.
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Now I see it..... a pearl sleuth follows each of the people listed in this thread, and more, and persuades each one to watch the actual experiment in time lapse. Then the sleuth video captures the expert in an opportunity to revise their opinions, based on scientific research. Heh. Heh. Maybe the LOL's will have to do it if we can't the get youth to do it for us. The Miss Marple brigade!
The SuperJeweler Blog

A pearl occurs when some sort of irritant works its way into an oyster. This irritant could be as simple as a grain of sand. Once the oyster recognizes a foreign element, it begins secreting a substance to surround that irritant to protect itself. It continues doing this, creating layer after layer, until the final result is a pearl.
Okay, so the difference between natural and man-induced pearls…
A natural pearl occurs when the pearl-creating process occurs without any human intervention. That is, when an ocean current carries a grain of sand into an oyster. As such, a perfectly round or white natural pearl is extremely rare and priced as such. Like diamonds, natural pearls need perfect conditions to form on their own.
Hey I did it! I attached it the way I wanted yay! :arms: