Abalone pearls
are very unusual. They are readily identified by their hollow structure and highly iridescent nacre and are formed in abalone shells.

Akoya pearls
are saltwater cultured pearls of Japanese origin and are formed by the Akoya oyster.

Baroque pearls
are neither round nor symmetrical, but very distorted and irregular in shape. Often the surface is very uneven and they occasionally resemble such objects as teeth, cacti, tadpoles, mushrooms, or snails.

Bib
is a pearl necklace with more than three strands.

Biwa pearl
are cultured freshwater pearls grown in Lake Biwa in western Japan.

Black-lip oysters
are found over a wide area stretching from the Cook Islands, eastward through Tahiti to the Tuamotu Archipelago and the Gambier Islands in French Polynesia. The black-lip oyster is responsible for producing the black pearl.

Black pearls
are naturally-coloured dark pearls from the black-lip oyster. The colour is black or very dark grey, however dark blue, dark green and purple-grey coloured pearls also come under the title of black pearl. Black pearls are rare.

Blemishes
are tiny surface irregularities that mar the uniformity of the exterior of the pearl.

Blister pearls
are natural pearls caused by the chance intrusion of a parasite through the outer shell of an oyster. The mollusk secretes nacre over the irritant, cementing it to the shell itself. Blister pearls are frequently irregular in shape.

Blue pearls
are dark-coloured pearls whose colour is derived from foreign contaminants in the nacre itself or between the nacre and the shell bead nucleus. Good examples of blue pearls are naturally-coloured, dark Akoya pearls, which may be blue, black, grey, or brown. Black and blue pearls may look similar but the difference is in the origin of their colour.

Choker length
refers to a pearl necklace 14 - 16 inches (35 - 40 cm) in length.

Clam pearls
have no nacre and are therefore limited in their commercial value.

Colour
of pearls is usually influenced by the type of pearl oyster; an important factor in pearl selection.

Conch pearls
are rare, non-nacreous pearls produced by the Queen conch and are characterised by a pink flame patter with a porcelain-like surface. They are found in the Caribbean.

Cultivation
refers to the process whereby an oyster or mussel is seeded, tended and harvested to produce a cultured pearl.

Cultured pearls
are pearls formed by the insertion of a piece of mantle tissue, with or without a nucleus, into the mother oyster or mussel.

Dog collar
refers to a multi-strand (as many as five) choker-length necklace, usually joined together with a single clasp.

Freshwater pearls
are flesh-nucleated pearls from freshwater shellfish produced in various countries around the world, including Japan, China, and America.

Gold-lip oysters
are found most commonly around countries such as Indonesia, Thailand and the Philippines. The oyster's inner shell edge is often golden yellow, and it usually produces yellowish or golden-coloured South Sea pearls.

Graduated strand
refers to a single strand of pearls with small pearls at each end that increase in size toward the middle of the strand. The centre pearl is usually much larger than the two on either side.

Grain
is a unit of measure for natural pearls; one grain equals 0.05 grams or ¼ carat.

Half pearls
are whole pearls that have been ground or sawed on one side, usually to remove blemishes. If about three-quarters of the pearl remains, it is known as a three-quarter pearl. The term 'half pearl' is also used to refer to blister or mabe pearls.

Hank
refers to the number of strands tied together at one end. These strands usually do not usually have clasps attached.

Imitation pearls
are any pearls entirely manufactured to look like natural or cultured pearls. There are two types: one variety is composed of hollow or solid glass beads coated with essense d'orient, which is produced from the scales of certain types of fish. The other variety, known as "shell-based pearls", are imitation pearls coated with a substance like nail polish and then lacquered. There are also numerous plastic imitation pearls on the market. See Mallorca.

Iridescence
refers to the optical effect whereby prismatic colours, similar to the ones seen on oil films, can be seen. Iridescence is the play of lustrous colours, which may be like those of the rainbow or a subtle combination of colours such as pink, blue, green, and silver.

Kan
is a Japanese unit of weight equaling one thousand momme, or 3.75 kilograms.

Kasumiga pearls
is a new type of Japanese cultured pearl from a lake north-east of Tokyo. The mussels are a crossbreed between Japanese and Chinese freshwater mussels, and are implanted with round or flat seeds. The resulting pearls are glowing in rosy hues from light to dark pink.

Keshi pearls
are small, roundish natural pearls formed accidentally in the soft tissue of the mollusk during the cultivation process. In Japanese, keshi means "poppy seed". These pearls are formed when small chips of the mollusk's shell break off and fall inside the mollusk during the surgical insertion of the bead. The mollusk treats these pieces as irritants and coats them with nacre.

Knotting
are small knots tied between each pearl in a strand to prevent the loss of pearls if the necklace breaks. Knotting usually adds from 2½ to 6cm to a necklace.

Luster
is the appearance of a pearl's surface judged by its brilliance and ability to reflect light. Also called "sheen" or "shimmer". See Orient.

Mabe pearls
are formed when a half-bead is cemented to the mollusk's inner shell. The mollusk covers the half bead with nacre and when the shell is cut off, the bead is exposed at the back. The bead is removed, the pearl cleaned (to prevent deterioration) and the remaining hole filled with paste, wax or sometimes with another bead and then covered with a mother-of-pearl backing. Mabe pearls must only be used in closed-back settings. Also referred to as a half-pearl or cultured blister pearl.

Mantle
is the part of an oyster's anatomy that secretes nacre. Tiny tissue fragments are used to stimulate pearl formation in pearl culturing.

Mallorca
is a name for imitation pearls taken from the island off the Spanish coast. Also known as "Majorca".

Matinee length
refers to a pearl necklace 20 - 26 inches (50 - 66 cm) long.

Mikimoto pearls
are pearls produced and marketed by the Mikimoto Company.

Mollusk
is any invertebrate having a soft body often protected by a shell. Includes the snail, bivalve (mollusk, clam, mussel), squid, and octopus.

Momme
is an ancient Japanese unit of weight, still used for cultured pearls. One momme equals 3.75 grams.

Mother-of-pearl
is the smooth, hard pearly lining on the interior of upper and lower shells of certain oysters and other mollusks, used to make decorative objects, buttons and beads.

Nacre (NAY-ker)
is the pearly substance secreted by the mantle of certain mollusks to form a pearl. Nacre also creates the beautiful mother-of-pearl coating found on the inside of pearl shells and several other varieties of shellfish.

Natural pearls
are formed entirely by accident and without the intervention of man. Either a parasite or other foreign substance is covered by nacreous layers inside the oyster.

Non-nucleated pearls
are formed by the insertion of tissue only. See Freshwater pearl.

Nucleus
is inserted into a pearl-producing oyster to speed up the pearl growing process. The nuclei act as the irritant upon which nacre is deposited, and are usually made from the shell of North American freshwater mussels.

Off-round pearls
are slightly flattened or ovalish in shape.

Opera length
refers to a pearl necklace 28 - 36 inches (70 - 90 cm) in length.

Orient
is the typical pearly luster seen on pearls or mother-of-pearl shell. Also known as iridescence.

Oriental pearls
are natural pearls found exclusively in the waters around Bahrain in the Persian Gulf. It is not a cultured pearl.

Pearl
usually refers to a natural pearl when no qualifying adjective, such as cultured or imitation, precedes it. According to CIBJO regulations, pearls are "natural formations secreted accidentally and without the aid of any human agency". However, this regulation may not always be adhered to since natural pearls make up such a tiny proportion of the trade.

Princess length
refers to a pearl necklace 16 - 20 inches (40 - 50 cm) in length.

Rope length
refers to a pearl necklace longer than 40 inches (100 cm); also called 'lariat' or 'saupier'.

Round pearls
are perfectly round in shape.

Seed pearls
are very small roundish pearls that form in the mollusk, often in addition to a larger cultured or natural pearl. They measure about 2mm or less and are usually too small to be used for jewellery.

Semi-baroque pearls
are not round in shape; examples are pear, drop, egg, and button shapes.

Shape
is one of the most important criteria in pearl selection. Pearls can be divided into four basic shape categories: round, off-round, semi-baroque and baroque.

Silver-lip oysters
are used mainly in Australia to cultivate South Sea pearls. This type of oyster produces silvery white pearls.

South Sea area
stretches from Burma and the Gulf of Thailand through the Sulu Sea of the Philippines, Malaysia, the Indonesian Arafura Sea and north-west Australia. It continues into the Cook Islands, eastward through Tahiti to the Tuamotu Archipelago and the Gambier Islands in French Polynesia.

South Sea cultured pearls
are produced in the saltwater areas of north-west Australia, Burma and some South Sea islands. The pearl-bearing mollusks found in this area are much larger than the Japanese variety and can accommodate a much larger nucleus. They also produce nacre at a greater rate, allowing the pearls to grow very quickly.

South Sea keshi pearls
are formed in the South Sea areas, these keshi pearls are larger than the Japanese variety and are frequently baroque in shape.

Torsade
is a multi-strand necklace formed by twisting strands around each other. A popular way to wear freshwater pearl strands.

Uniform strandis a strand whose pearls are all about the same size.