Natural pearls are very rare. They are, in fact, much more rare than diamonds. There is no scientific study available that definitively shows how rare a natural pearl is, but
…many experts believe it takes approximately 10,000 mollusks to find one fine natural pearl. However, in areas of Central America, there are places where natural pearls are much more prevalent. It is believe this is due to a higher parasitic concentration. Cultured pearls are not nearly as rare. In fact, all the pearls we see today in jewelry stores are cultured pearls. The natural pearl industry all but died nearly 100 years ago. Cultured pearls are pearls grown on farms where pearl mollusks are nucleated and then tended for a period of time, eventually producing a pearl. (MORE) 
