Contents
The Birth of a Pearl
Early Theories of Pearl Formation
It was only in the 16th century that naturalists began to draw up a truly scientific theory as to how pearls were formed. It became widely accepted that contrary to the popular belief of the time, a pearl did not, in fact, grow from a droplet of rain or dew. Initially, certain theorists believed pearls to be eggs that the oyster had failed to expel and which had become attached to the shell.
The Emergence of a New Theory
Gradually, though, another theory emerged: In the 18th century, Antoine Ferchault de Réaumur realized that the oyster began to produce pearls when fragments of shell irritated its body. In the mid-20th century, Filippo de Filippi observed freshwater mussels and noticed the presence of parasitic worms. It then became clear that foreign bodies such as sand, shell fragments, worms, or algae were behind the formation of pearls as the oyster defended itself.
Modern Understanding of Pearl Formation
Today we know that the protective shell is produced by the mantle. To grow in size or repair its shell, the oyster regularly secretes mother of pearl substance made of two elements based on calcium carbonate: aragonite and conchiolin. When an intruder gets inside the shell, the oyster will deposit the mother of pearl in a series of fine layers around the foreign body just as it does when making its own shell. These layers, composed of aragonite, are cemented together by a translucent film of conchiolin, giving the pearl its characteristic luminescent transparency and sheen.
