Each layer is translucent and allows some light to pass through to the lower layers. The light reflecting from the various layers combines to create the luster and a slight rainbow effect called iridescence. Although natural pearls are found all over the world, most of the natural pearls now harvested come from the Persian Gulf, Sri Lanka, the Red Sea, and the Phillipines. Smaller amounts come from near Venezuela and the Gulf of California. The cultured pearl industry is mostly located in the seas of Japan and Australia.
Japan produces more cultured pearls than any other country.
Most cultured pearls are produced in underwater farms, with the mollusks suspended at the right depth in baskets. This information was found in Compton's Interactive Encyclopedia.