Joan Lo Biondo, age 12, of Ridley Park, Pa., for her question:

WHAT IS THE DIFFERENCE BETWEEN A REAL AND A CULTURED PEARL?

Oysters produce both real pearls and cultured pearls, those lovely lustrous gems that make such exquisite jewelry. Real pearls are those that are formed naturally, while cultured pearls have a little help from man in developing. Mother Nature forms a pearl when a tiny grain of sand or other foreign matter enters the oyster's house and can't get out. The oyster's sensitive body reacts by gradually covering the unwelcome visitor with layer upon layer of nacre, a special pearly substance used to line two shells. Usually three to seven years or more passbefore the pearl is ready to join a necklace.    

Cultured pearls are real pearls, but are helped along by man. To do this, young oysters are planted in carefully selected oyster beds. After three years they are moved to special laboratories where trained persons insert a tiny pellet between their shells. Four years later, after careful precautions and monitoring, the oysters are opened and the cultured pearls are extracted. They are carefully washed, polished and graded before being sent to the market.