The best known pearl is the round pearl produced by saltwater oysters. The most famous of these is Japan's Akoya pearl. The finest Akoya pearls are more perfectly round than other pearls and have the highest luster. When they exceed 10mm in diameter, they command a very stellar price.
Biwa pearls are grown in freshwater (lakes and rivers) and derive their name from Lake Biwa in Japan. Until recently, the term "Biwa" was often incorrectly used for any freshwater pearl, yet today it is used only for those from Lake Biwa. Freshwater pearls are grown in many countries, including the US, Japan, and Ireland, but China is now the leading producer.
Some of the world's most prized and most beautiful pearls are natural freshwater pearls. These are very expensive and can compare in price to natural saltwater pearls. Frequently whiter than saltwater pearls, these pearls were cherished by the Romans. It was rumored that Roman legions would venture into England to search for rare pink freshwater pearls found in Scotland.
Cultured freshwater pearls also occur in interesting shapes, as do the natural. "Angel Wing" pearls are very collectable and can be found in the Mississippi River and other nearby rivers and lakes. Cultured pearl producers are also experimenting with special shapes, such as crosses, bars, ovals, lentils and more.
Freshwater pearls naturally occur in a wider range of colors than round saltwater pearls. Colors include light, medium, and dark orange, lavender, purple, violet, blue, rose, and gray. Large natural freshwater pearls in unusual colors can be very expensive (especially round ones). Be sure to ask whether a pearl is natural or not, as they can be dyed.
Baroque pearls are technically any pearl that is not round and has an interesting irregular shape. Do not confuse it with a round pearl that is simply "out of round". It must have a distinctive enough shape to be interesting and attractive. Baroque pearls are produced in saltwater and freshwater mollusks and can be natural or cultured. They have a distinctive appeal due to their very beautiful tints of color and iridescent flashes.
Mabe pearls (Mobe) are dome-shaped pearls. They are available in a variety of colors and shapes. The most common are the round or pear-shaped. They are a hollow blister that forms on the side of the interior of the oyster. They have a very thin nacre and are filled with epoxy with a mother-of-pearl backing. They require extra care, but are a large attractive look with affordability compared to other pearls similar in size. Still, a strand of coin pearls can be quite expensive depending on their quality of color, size,and luster.
Solid blister pearls are similar to the Mabe, but are not assembled. This type of pearl is produced in freshwater lakes in Tennessee. It's available in several shapes and has a distinctive appearance created by a mother-of-pearl background. This is retained from the shell lining when the pearl is removed. These pearls have unusually high luster and iridescence which make them more expensive than mabe pearls, but also more durable.
South Sea Pearls are produced in waters off of Australia, Indonesia, and the Philippines in saltwater oysters. South Sea pearls usually start at about 10mm in size and go up from there. Pearls from 11 to 14mm are the average and anything over that is considered very large. They are often less round and less lusterous than their smaller counter part from Japan. Still, they are very beautiful and very expensive, with the golden and fancy yellow in high demand today.
"Tahitian" black pearls are produced by a black-lipped saltwater oyster unique to the waters of French Polynesia and the Cook Islands. This variety of pearl is distinctive because of their unusual natural shades of color, including tones of gray, blue gray, gunmetal gray, brown black, or greenish black. The most expensive color in the Tahitian black pearl is black with an iridescent peacock green overtone. However, the Tahitian black pearl is often not uniform in color and can be darker on one end than the other. They are seldom smaller than 8mm and are rarely perfectly round. Remeber, however, not to confuse natural black color with a natural pearl, as most are cultured. In addition, beware of irradiated or dyed black pearls which are common and less expensive.