Pearl or parasite enters a bivalve mollusk and settles inside the shell. The mollusk, irritated by the intruder, forms a pearl sac of external mantle tissue cells and secretes the calcium carbonate and conchiolin to cover the irritant. This secretion process is repeated many times, thus producing a pearl. Natural pearls come in many shapes, with perfectly round ones being comparatively rare. Typically, the build-up of a natural pearl consists of a brown central zone formed by columnar calcium carbonate (usually calcite, sometimes columnar aragonite) and a yellowish to white outer zone consisting of nacre (tabular aragonite). In a pearl cross-section
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",