The rarest pearls (natural pearls) grow in the wild, but they are hard to find and are of course the most expensive. Cultured or farmed pearls make up the bulk of those that are seen on the market today. Cultured pearls are just as “real” as wild, natural pearls, and are created the same way – just with a little help. A tiny bit of shell, a bead or a piece of a living shell’s mantle is inserted into a freshwater oyster or mussel, and the shell is left for a period of time to naturally form the layers that eventually result in a pearl. Cultured pearls can only be distinguished from natural pearls by use of an x-ray. Imitation pearls are also widely used in costume jewellery, and these artificial pearls are usually easy to tell apart from the real thing simply by its less-iridescent appearance or depth of luster.