The pearl is the only precious stone quarried from the land. Then how is the pearl? It occurs in the shells of mollusks. This happens when the sink penetrate foreign particles. This can be sand, small inhabitants of the fauna, and so on. All of these can injure the body of the mollusk. To avoid this, it begins to secrete a special substance. It is called nacre and is translated as mother of pearl. This material coats the foreign body, smoothing out all the sharp corners. And formed pearls. The longer it is inside the shell, the larger it will be, because the substance of the clam layers envelops it, and it is released until the pearl leaves his home. This can happen when the diver gets it.