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
Pearl: The Best Collection Pearl: The Best Collection Pearl: The Best Collection (stylised as pearl ～The Best Collection～) is Kokia's first greatest hits album, released on February 1, 2006. It was released simultaneously with her first video clips collection, "". The album featured material from her time with Mother Land management under Victor Entertainment (2003-2006). In this time, Kokia had released two albums ("Remember Me" and "Uta ga Chikara"), along with seven singles. After working with Mother Land, she set up her own personal management company, Anco & Co., and has worked with them ever since. Three singles were released after "Uta ga Chikara",