Some imitation pearls (also called shell pearls) are simply made of mother-of-pearl, coral, or shell, while others are made of glass and coated with a solution containing fish scales called essence of the Orient. Although artificial pearls look good, they do not have the same weight or softness as real pearls and their luster will also be considerably dimmed.
A well-equipped gem laboratory can distinguish natural from cultured pearls by using gemological X-ray equipment to examine the center of a pearl. With X-rays it is possible to see the growth rings of the pearl, where the layers of calcium carbonate are separated by thin layers of conchiolin. Differentiating natural pearls from non-beaded cultured pearls can be very difficult without the use of this X-ray technique.
Natural and cultured pearls can be distinguished from imitation pearls using a microscope. Another method of testing imitations is to rub two pearls together. Imitation pearls are completely smooth, but natural and cultured pearls are made up of pearlescent platelets, which make both appear slightly grainy.
Value of a natural pearl
High-quality natural pearls are very rare jewels. Their values are determined similarly to those of other precious gems, based on size, shape, color, surface quality, orientation, and luster.
Individual natural pearls are often sold as collectibles or placed as centerpieces in one-of-a-kind jewelry. There are very few natural pearl strands to match and those that often sell for hundreds of thousands of dollars. (In 1917, jeweler Pierre Cartier bought the Fifth Avenue mansion that is now the Cartier store in New York in exchange for a double string of natural pearls that Cartier had been collecting for years; at the time, it was valued at $ 1 million ..) 
The introduction and advancement of the cultured pearl has hit the pearl industry hard. Pearl merchants have publicly disputed the authenticity of these new cultured products and left many consumers uncomfortable and confused about their much lower prices. In essence, the controversy has damaged the images of both natural and cultured pearls. In the 1950s, when significant numbers of women in developed countries were able to afford their own cultured pearl necklace, natural pearls were reduced to a small and exclusive niche in the pearl industry.
Origin of a natural pearl
Previously, natural pearls were found in many parts of the world. Today’s natural pearls are mostly confined to the seas off Bahrain. Australia also has one of the last pearl dive boat fleets in the world. Australian divers dive for South Sea pearl oysters for use in the South Sea cultured pearl industry. Catching pearl oysters is similar to how many oysters are taken during natural pearl days. Therefore, a significant number of natural pearls are still found in the waters of the Australian Indian Ocean from wild oysters. X-ray examination is necessary to positively verify the natural pearls found today.