Although most gemstones are minerals, gemologists include pearls and other organic materials such as amber, coral, ivory, and jet in their lists of precious gems. Pearls can be found in saltwater mollusks of the genus Pinctada or a few freshwater mollusks belonging to the family Unionidae.
It is generally believed that the Pearl originates in elephants, clouds, boars, conch-shells, fish, serpents, oysters and bamboos—of which oysters have the largest share in their production…Those Pearls that are found in the heads of elephants and snakes, are rarely to be had except by devout austerities; at present good Pearls are obtained from bamboos, oysters and conch-shells.
~S. M. Tagore
(1879 compilation and translation of ancient Hindu texts)
Although the ancients knew that pearls were found in mollusk shells, for centuries they did not know how they were formed. Some sources held that pearls were the eggs of female oysters. Still others believed that pearls were capable of breeding other pearls. Pliny the Elder (AD23–79), Roman author and naturalist, had another theory about the origin of pearls:
“When the genial season of the year exercises its influence on the animal [the mollusk], it is said that, yawning, as it were, it opens its shell, and so receives a kind of dew, by means of which it becomes impregnated; and that at length it gives birth, after many struggles, to the burden of its shell, in the shape of pearls, which vary according to the quality of the dew.”
Pliny went on to say that the quality and size of the pearls were affected by atmospheric conditions. “It is quite evident that the quality of the pearl depends much more upon a calm state of the heavens than of the sea, and hence it is that it contracts a cloudy hue, or a limpid appearance, according to the degree of serenity of the sky in the morning.” According to Pliny, lightning and thunder frightened the animal and spoiled the incipient pearl.
Pliny also had some interesting information about how pearls were harvested. “Some writers say that these animals live in communities, just like swarms of bees, each of them being governed by one remarkable for its size and its venerable old age; while at the same time it is possessed of marvelous skill in taking all due precautions against danger; the divers, they say, take especial care to find these, and when once they are taken, the others stray to and fro, and are easily caught in their nets.”
“Nasr writes—and his statement has received support from many quarters and many an observer has said the same thing—that when a diver intends to dive, he waits for the afternoon and the meridian, so that the sea gets lighted up and he can see whatever is in it. He then casts his gaze to and fro till it perches upon a shell which looks as if it is an even surfaced stone. Lying under the water it looks like a large plum to him although in reality it is the size of a grape…Around one side of his waist is tied a black stone weighing twenty-five to thirty mannas…The black stone is carried by the divers to scare away a creature in the sea of which they are afraid since it kills them. This creature flees at the sight of the black stone.”
“A man from Baghdad has said that the divers have devised a new method in our age, eliminating the need to hold back one’s breath. The divers can roam about in the sea from morn till noon; in fact, they can remain in the sea as long as they like. It is up to their employer and how much he pays them for their labours. This new device is made from skins which the diver puts on up to the portion of the body below the breast and tightens it round the ribs. He then makes the dive and benefits from the air inside the skin.”
As late as the 17th century, there was still some confusion about the origin of pearls. Some considered pearls to be a type of bezoar, a magical stone retrieved from the alimentary canal of animals. Thomas Nicols’ 1652 lapidary quoted Anselmus de Boodt, a Belgian minerologist and physician of some stature:
“I have taken out of these shell-fish many Margarites [pearls], and they are generated in the body of the creature, of the same humour of which the shell is formed…for when ever this little creature is sick or ill, and hath not strength enough to belch up, or to expel this humour which sticketh in its body it becometh the rudiments or beginnings of Margarites.”
Today we know that natural pearls are formed when a foreign object is trapped in the shell of a mollusk. In order to protect itself, the mollusk isolates the foreign article by covering it with nacre, the same substance that coats the animal’s shell. Layers and layers of nacre ultimately form a pearl. When pearls are cultured, or man-made, a tiny bead or piece of tissue is purposely inserted into the shell of the mollusk to start the process pearl formation.
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