Natural and cultured pearls are both produced in nature; and are both considered valuable and sustainable gems. Natural pearls are formed when an irritant accidentally gets into an oyster. Layers of coating are deposited on the irritant to make it smooth. A natural pearl is thus born. Cultured pearls are formed in the same process as a natural pearl, however a shell bead nucleus (the irritant) is inserted into the oyster through human intervention. Imitation pearls, a.k.a. fake pearls, are fully man-made using materials like glass and plastic. They have no real value as a gemstone.