How are pearls created?
Freshwater pearls are farmed in freshwater and grown in mussels. The irritants and the oysters used in culturing freshwater pearls are smaller than saltwater pearls. The technical produce is usually twenty or more pearls in one oyster. Most of them are coming from China.
Salt water pearls, are farmed in saltwater, and grown in oysters. Only one pearl is grown per oyster. This makes salt water pearls more expensive than freshwater ones. Countries known as producer of saltwater pearl are Thailand, and Philippines in South East Asia; Australia and Tahiti in South Pacific, especially in Tahiti, you'll find the beautiful black pearls.
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When a piece of gritty sand gets lodged in the oyster, kind of like getting something in your eye, the oyster secrets a substance called nacre to surround the irritation. Over time, the layers of nacre build up to form the pearl. The longer the irritant remains in the mollusc, the more layers of nacre and (usually), ...Go to the following site for a more in depth explanation:
The formation of a pearl begins when a foreign substance enter the oyster between the mantle and the shell, which forms an irritation in the mantle. It surrounds the irritant with layers of the nacre substance secreted which had been used to create the shell, which forms a pearl in the oyster shell.