A natural pearl is secreted accidentally by a mollusc without human intervention. It is one of nature’s most wonderful and fascinating gifts. Yet how is it created? How does it display such natural beauty, such shimmering glamour? The answer lies hidden within the animal.
Molluscs, less-than-attractive marine animals, live on the sea floor or riverbeds and feed on plankton or other organic nutrients suspended in the water. Should an irritant, for example, get into the mollusc’s shell and thus create a threat, nature activates a protective mechanism. The foreign object becomes encased in a soft tissue, the pearl sack. In the case of nacreous pearls, the object is then gradually covered by a smooth shiny substance called nacre, composed of a large number of minutely thin films of calcium carbonate crystals; a 1 mm pearl layer consists of approximately 2000 layers of crystal. The final size of the pearl depends on how many layers of nacre have formed around the intruder and this, in turn, depends on how long the pearl remains inside the mollusc. A pearl layer of one millimetre takes about five months to be grown, depending the mollusc genus. The formation of nacre is also influenced by a number of additional factors such as water and weather conditions, nutrients and the general health of the mollusc.
Any type of mollusc can – in theory, at least – grow a natural pearl. However, by far the largest number of natural pearls in the market comes from two types of saltwater oyster – the Pinctada ssp. and Pteria ssp. genera – and a large group of freshwater mussels – the Unionidae family.
See also the video presentation: Computer tomography of pearls
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