How is a pearl formed?

Natural and Cultured Pearls

Ever wondered how a pearl is formed and what the difference is between a natural pearl and a cultured pearl? If you have you wouldn’t be on your own. Read on to gain an insight to the wonderful world of pearls.

A pearl is formed within a living shelled mollusc, (Mollusca is an species of invertebrate animals). Not all pearls formed by molluscs are classed as valuable gem stones, let’s discover why.

A pearl begins when foreign matter, in the form of a small parasite or other organic material, enters the mollusc during respiration or feeding. If the matter becomes trapped within the folds of the protective membrane called the mantle, this irritates the mollusc.

This would be similar in comparison to ourselves getting grit in the eye. Where we would run to the nearest mirror or beg a friend to assist in the removal of the irritant, if unable to expel the aggravation naturally, the mollusc forms a sac around the pearl to isolate it. Nacre, also known as mother of pearl and pronounced nay-kah, is a combination of a protein called conchiolin and a mineral of calcium carbonate called aragonite. Together they form the hard iridescent layer of the inner shell of the mollusc. The aragonite supported by the conchiolin is deposited on the irritant producing layer upon layer of nacre to produce a pearl. The more layers of nacre laid, the larger the pearl.

Natural pearls are exactly that, natural,  wild pearls are rarely found in nature, hence the price tag they command. Sadly hundreds of pearl oysters are killed by man searching for the natural pearl, which is where cultured pearls come in. Although the formation and process of the pearl creation is the same, a cultured pearl is formed when the irritant, usually a piece of the mantle epithelium, is introduced with intention into the mantle and grown in pearl farms, many of which are found in Japan and China.

Nacre is produced primarily by two types of the Mollusca species, bivalves and clams.

The fresh water mollusc bivalves belong to the family of Unionoida which are freshwater mussels and Veneroida which are fresh water clams.

The pearl oyster is a salt water bivalve oyster and belongs to the Pteriidae family, within the genus Pinctada.
Please be advised this family of Mollusca is not to be confused with the Osteidae which includes most of the molluscs commonly consumed as edible oysters, unless that is, you like playing a game of chance with the possible outcome of a fractured tooth.

Toni Hardwick