Cultured pearl is calcium carbonate and a fibrous protein called conchiolin. As the nacre builds up in layers of minute aragonite tablets, it fills the growing pearl sac and eventually forms a pearl. Natural pearls are formed by nature, more or less by chance. On the other hand, cultured pearls are human creations formed by inserting a tissue graft from a donor oyster, upon which a pearl sac forms, and the inner side precipitates calcium carbonate, in the form of nacre or "mother-of-pearl". The most popular and effective method for creating cultured pearls are made from the shells of freshwater river mussels
Parable of the Pearl writings. Pope Pius XII used the phrase to describe virginity. The pearl itself is a beautiful, single entity, formed through suffering in the heart of the oyster (in the same way that believers endure lack of wealth or comfort) and like the Church, will be put on display in a coming day. Unlike precious stones which must be cut and polished to reveal their clarity and beauty, the pearl is perfect as it comes from the oyster. A version of the parable also appears in the Gnostic Gospel of Thomas (Saying 76): This work's version of the parable of the