Composition - Calcium carbonate,
conchiolin and water ; Hardness - 3
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 players produces a characteristic iridescent lustre, also known as the “orient of pearl”. In cultured pearls an irritant is introduced to initiate the formation of a pearl. In a “nucleated” cultured pearl a small bead is used as the nucleus, upon which the layers of nacre are secreted. Pearls vary in colour 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.
OCCURRENCE
Natural pearls have been harvested from the Persian Gulf, the Gulf of Manaar (Indian Ocean) and the Red Sea for thousands of years. The coasts of Polynesia and Australia produce mainly cultured pearls. Both freshwater and saltwater pearls are cultivated in Japan and China. Fresh water pearls occur in the rivers of Scotland, Ireland, France, Austria, Germany and Mississippi (USA) .
REMARK
Pearls were once thought to be the tears of the gods.
