Pearl jewelries refer to the jewelry made of different pearls. Pearls jewelry holds their value due to the rarity of "mother nature" creating this form of jewelry. The prices of pearls though, have confused many novice buyers. Few seem to understand how one strand of pearls can cost them $300, while another similar looking piece can cost $40. Just like diamonds, there are many factors that contribute to the price of a pearl. There are two main types of pearl jewelry, those that occur naturally and those that are cultured. Naturally occurring pearls hold a significant value due to the rarity of pearls being produced. Of the 8,000 or so species of oysters, only about 20 of those are able to constantly produce pearls. For the most part the pearls these oysters do produce, few maintain a round or spherical shape. Somewhere in the 19th centaury science found a way to produce synthetically. These are called cultured pearls. Most of today's pearl jewelry is made in this way. The process involves surgically implanting the agent that causes the process of creating the pearl and creating a farm like environment for their stable of oysters. Although each variety of oysters creates a different style of pearl, cultured pearls are easily able to create the spherical shape most consumers The size of the pearl will also affect the price of our pearl jewelry. In general the size is measured using the diameter of the pearl and expressed in millimeters. Even a millimeter difference can create a 100 percent or more difference in value.