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
Parable of the Pearl story. However, those who do not believe in the kingdom of heaven enough to stake their whole future on it are unworthy of the kingdom. This interpretation of the parable is the inspiration for a number of hymns, including the anonymous Swedish hymn "Den Kostliga Pärlan" ("O That Pearl of Great Price!"), which begins: <poem> O that Pearl of great price! have you found it? Is the Savior supreme in your love? O consider it well, ere you answer, As you hope for a welcome above. Have you given up all for this Treasure? Have you counted past gains as