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This Tiffany brooch, c. 1904, featuring Mississippi River pearls, flaunts the exquisite beauty of pearls.
© AMNH |
Over the millennia, different civilizations have come up with all sorts of theories to
explain the presence of these mysterious treasures from the bottom of the sea.
Ancient Romans theorized that pearls were the frozen tears of the oysters—or maybe even those of the gods—somehow captured by the shellfish. Lightning was seen
by the ancients as the ephemeral precursor of all sorts of natural anomalies, and the ancient Greeks thought the bolts might cause pearls to form when they
struck the sea.
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Blister pearls (attached to the inside of the shell) and free pearls of the freshwater Triangleshell Pearl Mussel (Hyriopsis cumingii).
© AMNH |
A popular
theory that persisted from antiquity all the way up to the 17th century, and originated in Arabia, Persia, or India, was that pearls were
formed from solidified raindrops or dew that had been caught in the gaping "yawn" of bivalves. The Roman scholar Pliny the Elder expanded upon
this notion, commenting that pearls "vary according to the quality of the dew."
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Beginning in the 17th century, scientists described pearls as everything from a secretion of a "viscous humour" within
the mollusk to undeveloped eggs to signs of disease or entombed parasites. The last two descriptions aren't too far off the mark. Contemporary science defines
the pearl as a calcareous body composed of concentric layers around a central nucleus that is organically formed by a living mollusk. Pearls are formed when a
small object irritates the shell-producing tissues of a mollusk, which causes the animal to encase it in a capsule of lustrous shell called nacre. The irritant
is most often a small bit of organic material, such as a particle of food, a tiny animal, like a pea crab, or another little crustacean—not the apocryphal
"grain of sand."
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This blister pearl (seen in cross-section) from the shell of a Red Abalone (Haliotis rufescens), formed around an Abalone Piddock (Penitella conradi) which drilled into the abalone shell from the outside. Following the death of the piddock, a small nestling bivalve (Hiatella solida) took up residence in the cavity.
© AMNH |
The future may yield more theories about the pearl—who knows? But through the ages, all have agreed on one thing: pearls are beautiful.  Learn more about pearls through one of the American Museum of Natural History's current exhibitions, Pearls.
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