Formation of a pearl inside a pearl oyster occurs because of the presence of foreign material inside the body of the oyster. To save itself from the undesired material the mollusk coats the object with layer after layer of nacre. It takes many years for a mollusk to produce a pearl of substantial size. The process through which the pearls are formed inside the body of the mollusk is very delicate, and a little disturbance at any stage of development of a pearl can influence its shape and lustre. The finest pearl is that which has no foreign matter in its core. Pearls are obtained from eight sources, which are Sky Pearl, Cobra Pearl, Bamboo Pearl, Hog Pearl, Elephantine Pearl, Conch Pearl, Fish Pearl and Oyster Pearl.