The prices of pearls vary widely as a result of shine, size, evenness or smoothness of the surface, shape and beauty, how they were grown, and color. Because they are rare, natural pearls are the most expensive. There are cultured pearls, which are more expensive than freshwater pearls. Akoya Pearls are highest quality saltwater cultured pearl, that comes primarily form Japan and China. The finest natural pearl come from Persian Gulf. Other sources of natural pearl are Gulf of Mannar, Indonesia, Gulf of California, Gulf of Mexico, islands of South Pacific and few other places.
In the past, pearls were tested by rubbing them against one's teeth. If a pearl is real, it will feel rough like sand pager. If it is fake it will feel too smooth. Nowadays, the most reliable method of testing to determine whether a pearl is natural or fake is a combination of the X-radiography and X-ray fluorescence testing procedures.
Large pearls are more expensive due to being rare. Pearls are measured in millimeters and even one millimeters in size difference could result in huge increase in the price. Round pearls are more valuable.