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158370.  Wed Mar 21, 2007 11:58 am Reply with quote

What's at the middle of a pearl?

F: Sand, grit

A: A worm, normally.

Often a nematode worm.

Contrary to popular belief, pearls hardly ever result from the intrusion of a grain of sand (inorganic material) into an oyster’s shell. Instead a pearl forms when an organic irritant becomes trapped in the mollusk.

An organic irritant can be a result of injury or an intruding parasite. The animal senses the foreign object and coats it with two materials—a mineral and a protein—that results in mother-of-pearl, the substance called nacre (NAY ker).


It can take anywhere from a few months to many years to form a pearl, depending upon its size. And different mollusks produce pearls at different rates. For example, the Black-lipped Pearl Oyster forms one to seven sheets of nacre per day.... Ideally, for most cultured pearls, the “grow out” period lasts between two and three years

The irritant inserted into a cultured pearl is The matter inserted is "a bead nucleus and a piece of mantle tissue from another pearl oyster. The bead will become the center of the pearl and the mantle graft will form the pearl sack, which will secrete layers of nacre onto the bead."

Pearls are "found in perhaps one of every 100 animals, and only one in ten of those are of good quality."

158371.  Wed Mar 21, 2007 12:01 pm Reply with quote

One of the reasons why you don't find pearls in your oyster dinners is that the pearl oyster is a different species from the edible oysters, which do not produce nacre - so they don't make pearls (though they do produce a similar thing that looks like a pebble).

158373.  Wed Mar 21, 2007 12:01 pm Reply with quote

A pearl’s natural color depends mainly on the species of mollusk involved. The color of the pearl tends to match the inside of the mollusk’s shell—black pearls are made by the Black-lipped Pearl Oyster, gold pearls are produced by the Silver- or Gold-lipped Pearl Oyster, etc. The pigment resides in the organic layers, between the layers of aragonite, a crystalline form of the mineral calcium carbonate.

158375.  Wed Mar 21, 2007 12:03 pm Reply with quote

This is a description of pearl diving in 1920s Dubai:

Each diver wears a clip like a clothes-peg to close his nostrils, leather sheaths protect his fingers and enable him to (wrench) the shells from the rocks underneath the sea, and each of his big toes is guarded by a similar sheath. He descends on a rope which has a stone weight attached to it. This is hauled up when he reaches the bottom. Round his neck is slung a string bag, which he fills with shells, attached to a rope with which his comrade, the puller, draws him up again when he gives the signal. Divers remain below the surface for nearly a minute and a half, and they descend about 30 times in one day, often to a depth of 14 fathoms. The shells are heaped on deck during the day and opened in the evening under the vigilant eye of the captain, who puts away the pearls in his sea chest. No diver knows whether it is his shell that contained a pearl. While the men are working they take neither food nor drink, but they eat in the early morning and after sunset they have a meal of rice and dates and fish. The shells are thrown back into the sea, the divers believing that oysters feed upon the empty shells. They believe too, that drops of rain which are caught by the oysters at night form pearls.

The work is very strenuous and conditions are hard, but the divers on the whole are healthy and many of them show unusually fine muscular development...

…The men are paid no wages, but they receive a share in the profits of the season. Divers are entitled to twice the amount which is paid to a puller, as their work is more arduous.

The same system has been used in various places around the world: for example the Ama women divers of Japan, the Sulu divers of the Philippines and, greatest of them all, the Paumotan divers of the central Tuamotu Archipelago in French Polynesia who could descend to depths of more than 120 feet where they work for up to two minutes. In the Tuamotus the pearl divers make eight to ten dives per hour during five to six hours.

158378.  Wed Mar 21, 2007 12:04 pm Reply with quote

<<MYTHCONCEPTIONS: Itchy oysters by Mat Coward

THE MYTH: Natural pearls are formed when a grain of sand or some other gritty substance becomes trapped inside an oyster’s shell; the creature covers the foreign body with secretions to prevent itself being irritated to death.

THE "TRUTH": If this were true, pearls - the only gems made by a living organism - would presumably be exceedingly common, given the amount of gritty grains the average bivalve must encounter in its lifetime. In fact, oysters (and the various other species which produce pearls) ingest and expel sand and the like all the time; it’s mere housekeeping, and nothing worth getting the nacre out for. That pearly substance is reserved for dealing with more serious intruders: parasites, such as drilling worms, which bore through the oyster’s shell. The host’s only defence is to isolate the parasite by entombing it in mother-of-pearl. The “princess and the pea” piece-of-grit theory, though debunked about a century ago, continues to enjoy almost universal currency.

SOURCES: Jack Ogden of the Gemological Association of Great Britain on _Woman’s Hour_, BBC Radio 4, 18 July 2006;;

DISCLAIMER: When one longstanding belief replaces another, forteans narrow their eyes and adopt a sceptical mien. If you wish to argue in favour of the dear old grain of sand, please cast your pearls upon our letters page.

164890.  Wed Apr 11, 2007 10:11 am Reply with quote

Cultured emeralds are created by a comparable process: post 164874.

Molly Cule
165638.  Fri Apr 13, 2007 6:49 am Reply with quote

Pearls CAN be formed by a grain of sand or grit but there is only a thousand to one chance of a pearl forming that way.

s - Jewels - a secret history

Most pearls are formed by a small parasite that dies inside the shell. In a river mussel the parasite squeezes in through a crack between the mussel’s shells hoping to live off the muscles flesh. The mussel realises it is there and tries to get rid of it, this makes the parasite roll around in a panic. When the parasite tires the mussel covers it with nacre to make it smoother and less irritating. It keeps on covering it for its life trying to get rid of it. The French natural scientist Raphael Dubois said ‘The most beautiful pearl is nothing more, in fact, than the brilliant sarcophagus of a worm’. The mussels with the parasites in them are spurned by mussel society and go and live under rocks out of the way, this makes it easier for pearl-fishers to find them.

Molly Cule
165639.  Fri Apr 13, 2007 6:52 am Reply with quote

The old word for pearls in English is ‘unions’, which comes from the Latin union meaning unique. Each location creates different pearls. The word pearl comes from ‘pig’s leg’ as mussel shells used to be much bigger and look like a pig’s back leg.

Pearls used to grow all over the British Isles, pearls from NW of Inverness in the Oykel river are rose pink. The bright colours in river pearls come from peat.

Rivers with pearls also have salmon. The salmon help the life cycle of mussels, which produce pearls. The mussels mate in an orgy, after each orgy the female produces about 200,000 spat (young) that hitch a lift on the gills of salmon. The spat grow on the salmon gills all winter, in the spring they drop off once the salmon is upstream and become mini-mussels which go onto make pearls.

165656.  Fri Apr 13, 2007 7:31 am Reply with quote

Oh, you're already here. You were saying:

In 18th C England, if you popped into a posh house for tea you might see the maids decked out in fine pearls. This was because they were keeping them luminous for their mistress. Pearls need humans to be beautiful. If they are left in a bank vault they turn yellow, next to human skin they become luminescent.
S Jewels – a secret history.

165672.  Fri Apr 13, 2007 8:02 am Reply with quote

Molly Cule wrote:
In a river mussel the parasite squeezes in through a crack between the mussel’s shells hoping to live off the muscles flesh.

I thought pearls came from oysters, or have I missed a meeting?

Molly Cule wrote:
When the parasite tires the mussel covers it with nacre to make it smoother and less irritating.

I realised I've been reading the thread about noranges and numpires too much when I thought "the mussel covers it with an acre of what?"

165676.  Fri Apr 13, 2007 8:08 am Reply with quote

Pearls can be found in mussels, clams, whelks, conchs, abalones and snails as well as in oysters.

165685.  Fri Apr 13, 2007 8:26 am Reply with quote

Blimey. You learn something new every day.

Next time I kill a snail in the garden, I'll be sure to check it for pearls first.

165705.  Fri Apr 13, 2007 9:13 am Reply with quote

Don't forget to beat the tits off it first.

Molly Cule
165719.  Fri Apr 13, 2007 9:32 am Reply with quote

How to make a cultured pearl – relax a two year old oyster by putting them in a warm bath. When the shells open stick in a thin sharp instrument (designed for the purpose by dentists) and use it to cut the oyster’s balls open. Insert a polished bead made of shell and a 2mm square of the frilly mantle of another oyster. Leave the oyster for about 3 months to recover from the trauma. If it doesn’t die then it will start making a pearl.

This process was created by a Japanese man called Mikimoto. He said “I want to live long enough to see the day when we have so many pearls we can sell necklaces for 2 dollars to every woman who can afford one and give them away free to every woman who can’t.”

Molly Cule
165720.  Fri Apr 13, 2007 9:33 am Reply with quote

Dr Bob - Freshwater pearls come from mussels and sea pearls from oysters


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