J U N E

PEARL

Pearls are formed in shellfish – especially oysters and mussels – as a natural defence against an irritant, such as a piece of grit. Layers of aragonite, known as nacre, are secreted around the irritant, and gradually build up to form the solid pearl. Light reflecting from these overlapping layers produces a characteristic iridescent lustre, also known as the “orient of pearl”. In cultured pearls and irritant is introduced to initiate the formation of a pearl. In a “nucleated” cultured pearl a small bead is used as a nucleus, upon which the layers of nacre are secreted. Pearls very incolour from white, white with a hint of colour (often pink) to brown or black, depending on the type of mollusc and the water. They are sensitive to acids, dryness, and humidity, and so are less durable than many other gems.