Natural Pearls

Definition

Natural pearl formations secreted in the interior of mollusks without human intervention. They are composed of a complex scleroprotein named conchiolin and of calcium carbonate in the form of aragonite and or calcite arranged in concentric layers. Natural pearls may be nacreous or non-nacreous.

Historical overview

Pearls were already discovered in prehistoric times. Before jewelers learned to cut gems, the pearl was of greater value than the diamond. In the Orient, pearls were ground into powders to cure anything from heart disease to epilepsy, with possible aphrodisiac uses as well.

Countless legends from all countries pay testimony until today to this origin. Respectful reverence marked man’s first contact and later the pearl became a cultural object to which mystical and magical properties were attributed.

The oldest Chinese history book, the Shui ging, mentions “strings of not completely round pearls” that were given to the great emperor in the third millennium BC. Pearls from the Pacific Ocean were probably known at an even earlier date, most certainly long before Europeans made their crossing.

For a quite a long time, pearls became treasures, a symbol of wealth, power and prestige and at the same time they were met with devotion and respect. Until today, the pearl has remained a symbol of purity that is traditionally used in wedding jewelry. Up to the present time the pearl is distinctly more than a tribute of fashion.

Natural pearls continued to have a regular market until the nineteen fifties. After this, until today, they have had a small but fine market for themselves.

Formation of natural pearls

The formation of a pearl is the result of a rather accidental occurrence within the normal life cycle of a mollusk. It is essential that epithelium cells of the upper epithelium layer of the mantle are transferred into the connective tissue, where they proceed to form a closed cyst, which is called the pearl sack.

The mantle grows onto the inner rim of the shell by means of a narrow double line that serves to hermetically seal the inner space between mantle and shell. This means that objects from the outside can only reach the inside of the mullusc if the mantle tissue suffers an injury. It is possible that a small fish may attack or bite the outer mantle rim, which occasionally protrudes from the shell, thus causing a transfer of epithelium cells and providing the reason for the formation of a pearl.

Another theory suggests that foreign objects may cause upper epithelium cells to deepen into the connective tissue where they will finally close into an epithelium sack that surrounds the intruder and separates from the upper epithelium layer.

Properties of Natural pearls

Fishing

The most important pearl fisheries in the past were in the Persian Gulf and the Gulf of Manaar which between Sri Lanka and India. Fishing still continues in these waters, but to a much reduced extent owing to pollution and changed economic circumstances. Off the northern costs of Australia, pearls are recovered in the course of fishing for mother-of-pearl shell. Other areas include the Pacific Islands, the Red Sea, Venezuela and the Gulf of Mexico.

Imitations

Imitations of pearl are usually easy to recognize, once the gem tester is familiar with their surface textures. The main problems arise in distinguishing between natural and cultured pearls. Both nucleated and non-nucleated cultured pearls are common, and different methods may be necessary to recognize them.