Why does an oyster make a pearl?
Oysters coat the inside of their shell with a very smooth form of calcium carbonate known as “mother of pearl”. If a piece of foreign material gets inside the shell and becomes stuck, the oyster coats the object with this material to minimize the irritation. Over time, the layers get thicker and a pearl forms. The oysters which produce pearls are not the same kinds people ordinarily eat. Pearl oysters are tropical and are cultivated in the south Pacific. They have flat, broad shells and look more like scallops than oysters. Ordinarily, many hundreds of oysters had to be opened to find one which contained a pearl. The Japaneese then learned how to grow pearls artificially. The secret lay in introducing a piece of foreign tissue into the shell, along with a “seed pearl”. These seeds are clam shells which have been formed into small spheres. The oyster then coats the clam shell with a pearl layer. This made pearls much less expensive, even the very rare and expensive “black” pearls.
