Oriental Pearls:   Natural pearls found in oysters of the Persian Gulf or those that look like pearls found there (according to the USA Federal Trade Commission). Sometimes this term is used to designate either any natural saltwater pearl or else more specifically, any natural saltwater pearl found in the West Asia Area, e.g. in the Red Sea, the Persian Gulf or the Gulf of Mannar
off the west coast of Sri Lanka.

A more precise definition of "Oriental pearl" is given by the respected pearl researcher, Koji Wada, in Pearls of the World : "natural pearls from one kind of sea-water pearl oyster called the wing shell."

Biwa Pearls:   Freshwater pearls cultivated in Lake Biwa, Japan's largest lake Sometimes other freshwater cultured pearls are called Biwas in order to impress buyers. Lake Biwa was one of the first freshwater culturing sites and it has been noted for its high quality pearls. Because of pollution, production has come to a standstill.

Kasumiga:  Pearls named after Lake Kasumigara, north of Tokyo, where they are cultured in Hyriopsis schlegehi x Hyriopsis cumingii hybrid mussels. Kasumiga' pearls, which have also been generically called Kasumi pearls, were introduced to the market in the mid 1990's and are only available in limited quantities. These nucleated freshwater pearls range in size from 11-16 mm and in color from purple to pink to white to gold.

Blue Pearls:  Dark-colored pearls found in oysters such as the Akoya or silver-lip oysters. The color is due to foreign contaminants in the nacre or between the nacre and shell bead nucleus unlike black pearls whose color is an inherent characteristic of the pearl nacre.

Half Pearls:  "Whole pearls that have been ground or sawed on one side, usually to remove blemishes" (as defined in The GIA Jeweler's Manual). If the sawed pearl looks too large to be a half pearl, it's called a three-quarter pearl . Half and three-quarter pearls are priced lower than whole pearls of the same shape and quality. Button and acorn shape South Sea pearls have a flattened side which can make them look like a half or three-quarter pearls when mounted.The term "half pearl"; is sometimes used to refer to blister pearls.

Blister Pearls:  Natural or cultured pearls that grow attached to the inner surface of the oyster or mussel shell. When cut from the shell, one side is left flat with no pearly coating. (Some people apply the term blister only to natural pearls of this type. Cultured blister pearls are not new. As far back as the 13th century, the Chinese were placing small lead images of the sitting Buddha inside freshwater mussels against their shells. The resulting pearly buddhas were either removed and sold as good-luck charms or else left attached to the shell and used as an ornamental curiosity.

Tennessee is a major source of cultured solid blister pearls. These American blister pearls come in a variety of shapes and are marketed under the name of domd. Their nacre is thicker than that of mabe pearls, making them more durable.

Mabe Pearls:  Assembled cultured blister pearls(pronounced MAH-bay). The blister pearl is cultured by gluing against the inside of the shell a half-bead nucleus (often of plastic or soapstone). After the mollusk has secreted nacre over the bead, the blister pearl is cut from the shell; and the bead is removed so the pearl can be cleaned to prevent deterioration. The remaining hole is filled with a paste or wax (and sometimes also a bead) and then covered with a mother-of-pearl backing. Mabe pearls are not as not as durable as solid blister pearls.

It can be hard to distinguish between mabe, blister or half pearls when they are mounted in jewelry. As a consequence, these three terms often end up being used interchangeably.

Despite all the work involved in assembling mabe pearls, they are relatively inexpensive for their large size. This is partly because several can be grown in one oyster and because they are grown in oysters that have rejected a whole nucleus or that are judged unsuitable for producing whole pearls. Also, any type of half pearl will cost far less than if it were whole, no matter what type of oyster it is grown in.

Most large mabe assembled pearls come from the silver-lip or black-lip oysters, but technically the term "mabe" should only refer to pearls cultivated in mabe oysters (Pteria penguin). The true mabe-oyster pearls are known for having a better luster, color and iridescence than pearls cultured in other oysters and are, consequently, more valuable. Most of those harvested are '/z or 3/a blister pearls. If a salesperson claims that the jewelry you are buying is made with a mabe-oyster pearl, have him or her write this on the receipt. It's helpful for insurance and appraisal purposes. Information on the cultur­ing of mabe oysters can be found in a write-up by Morimitsu Muramatsu in Pearls of the World.

"Mabe Blister Pearls":  An informal term used by some Pearls" dealers to designate mabe pearls with a rim, making them resemble a fried egg. The term "blister mabe" is also used. Technically, though, all assem­bled mabe pearls originate as blister pearls and after they are assembled, they are mabe pearls with a rim

"Rainbow pearls":  A trade name for pearls from the Western winged (rainbow-lipped) pearl oyster (Pteria sterna), which is noted for its high luster and rainbow-like colors. This oyster ranges naturally off the eastern Pacific Coast from California to Peru. Some are cultivated as mabe and whole pearls near Guaymas, Mexico.

"Rainbow pearls, "  which are generically called "black pearls, " are found in a variety of colors: lavender, pink, red, blue, green, purple, silver, gold, black and brown with varying shades and combinations. It's not unusual to see three or four color variations on one pearl. Whole cultured rainbow pearls range from 7 to about 12 mm in diameter and have a good nacre thickness. Their natural counterparts are found in sizes from seed to 30-carat pearls and range in price from $100 per carat to $2000 per carat wholesale. Cultured rainbow pearls cost less, with mabes being the least expensive.

Seed Pearls:  Small, natural pearls which measure about two millimeters or less. They usually weigh less than 0.06 carat.