Pearl Glossary
Each term below has a one-sentence definition in plain English, a note where the sources add detail or disagree, numbered sources and, where there is one, a link to the page that covers it. Link to any term with its anchor, for example /glossary/#nacre. The glossary has 150 terms and will keep growing.
A
AAA grade
A letter grade, from A up to AAA, that some sellers use for pearl quality; no standard defines it, so one seller's AAA need not match another's.1 2 3
GIA's journal describes the trade's grading systems as competing, often company-specific methods with coded terminology (2021), and CIBJO has no classification system of its own (CIBJO 2025 guide). Writing about tanzanite, GIA notes that companies may create their own AAA, AA and A descriptions.
Abalone pearl
A natural pearl from an abalone, a sea snail of the genus Haliotis, usually in mixed shades of blue or green.4
CIBJO places these snails in the Pacific, Atlantic and Indian Oceans (5.2). Abalone also produce blisters, and cultured blisters are grown in places such as California and New Zealand (9.1).
Adductor muscle
The muscle joined to both halves of a bivalve's shell, which closes the shell when it contracts.4
CIBJO 5.3.
Akoya cultured pearl
A cultured pearl grown around a shell bead in the Akoya pearl oyster, Pinctada fucata, mainly in Japan, China and Vietnam.4 5
Akoya is the Japanese name for the oyster (CIBJO 9.3). Freshwater pearls sold as "freshwater Akoya" are not Akoya (GIA).
Aliger gigas
The queen conch, a large sea snail of the Caribbean and Central America that produces conch pearls, pink and other colors, and a few cultured pearls.4
It was formerly named Lobatus gigas and is still called Strombus gigas in industry texts (CIBJO 9.5). Its entry refers to CITES, the convention on trade in endangered species.
Aragonite
The form of calcium carbonate whose microscopic platelets, bound together by conchiolin, make up nacre.4
Natural pearls can also contain calcite, another form of calcium carbonate (CIBJO 5.136).
B
Baroque
A natural or cultured pearl with an irregular, non-symmetrical shape.4 6
Baroque was originally a French adjective for objects that were not symmetrical (CIBJO 5.16).
Basra pearl
A natural pearl from the Arabian Gulf, produced by the pearl oyster Pinctada radiata.4
CIBJO also defines the Bahraini pearl, a natural pearl from the same oyster in Bahraini waters (5.15, 5.17).
Bead (nucleus)
The small sphere, usually cut and polished from freshwater mussel shell, that is inserted into a mollusk so a cultured pearl forms around it.4
Beads range from about 2 to 14 mm depending on the species, and are sometimes other shapes, such as coins (CIBJO 5.144). A pearl grown on an unusual bead must say so, for example "atypical bead cultured pearl" (CIBJO 5.18).
Beaded cultured pearl
A cultured pearl grown around a bead that was inserted into the mollusk together with a piece of mantle tissue.4
Bivalve
A mollusk whose shell is in two parts, such as an oyster, mussel, clam or scallop.4
CIBJO defines bivalves as members of the class Bivalvia (5.21). The adductor muscle, attached to both halves, or valves, closes the shell when it contracts (5.3).
Biwa cultured pearl
A freshwater cultured pearl, with or without a bead, grown in Lake Biwa, Japan, in the mussel Hyriopsis schlegelii.2 4 7
US rules allow the name only for cultured pearls grown in freshwater mollusks in the lakes and rivers of Japan (16 CFR 23.21(h)). CIBJO's 2025 guide says the mussel is native to Lake Biwa.
Black pearl
A naturally black natural or cultured pearl from the black-lipped pearl oyster, Pinctada margaritifera, or from Pinctada mazatlanica or Pteria sterna.4
CIBJO uses the name only for pearls whose color is natural, not caused by later processing (5.23, 5.24), and counts Tahitian cultured pearls among them (5.23).
Bleaching
A treatment that removes or changes a pearl's color with chemicals, physical agents or light.2 4
Bleaching is common for Akoya and for Chinese freshwater cultured pearls (CIBJO 2025 guide). CIBJO's standards say that cleaning doesn't include bleaching (4.4.2.1, 4.5.2.1), and require bleaching to be disclosed when natural or cultured pearls are sold (4.4.2.2, 4.5.2.2).
Blister pearl
A pearl that grew attached to the inside of the shell, so that its outer layers continue into the shell's own lining.4
CIBJO defines both natural (5.134) and cultured (5.53) blister pearls; in the Arabian Gulf natural ones are called "Nimro". A mabe is different, because it is assembled.
Bodycolor
The dominant overall color of a pearl, which every pearl has.4 6
Bombay bunches
Strands of round natural saltwater seed pearls, from under 1 mm to 3 mm across, sold in bunches mostly in Europe.4
CIBJO notes they mostly have medium to high luster and well-matched color (5.27).
Bombay pearls
A commercial name for natural pearls, mostly from Pinctada radiata, fished in the Arabian Gulf and Red Sea and exported through Bombay, now Mumbai, in India.4
CIBJO 5.28.
Buffing
Removing organic residues from the surface of natural and cultured pearls after harvest.4
CIBJO counts buffing, like polishing, among the normal procedures that don't need to be disclosed (5.31, 5.143).
Button-shaped
Describes a pearl with a symmetrical dome shape, with or without a flattish base.4 8
CIBJO also uses the French form, bouton (5.32). GIA counts button among eight basic pearl shapes.
C
Calcareous concretion
The technical name for the hard, pearl-like objects that almost any mollusk can produce.7 9
The FTC's definition of a pearl begins "A calcareous concretion" made of layers of carbonate of lime and organic material (16 CFR 23.19(a)).
Carat
A unit of weight equal to 200 milligrams, or a fifth of a gram.4
CIBJO 5.33. Natural pearls are often weighed in grains, a quarter of a carat each (5.87).
Chambered nautilus
A tropical Pacific relative of the octopus whose curved, nacreous shell is cut to make coques de perles.4
CIBJO describes it as little changed for more than 150 million years, with more than 90 tentacles, swimming by jet propulsion (9.14, 5.50). Its entry refers to CITES.
Chaw
A system for converting a pearl's weight into a volume figure, often used to sell pearls in the Arabian Gulf and India.4
CIBJO gives the formula as the carat weight multiplied by itself, then by 0.6518 (5.36).
Chinese drilling
Two drill holes made from two points on the same side of a pearl, usually its flatter side, that meet inside it.4
The technique was designed so pearls could be used as buttons (CIBJO 5.37). CIBJO's standards require it to be disclosed on natural pearls (4.4.2.1).
Chocolate pearl
A name for cultured pearls with a brown "chocolate" color, which in the pearls GIA studied came from treatment.10
GIA found that the brown was most likely made by bleaching the organic components of black cultured pearls, with no foreign coloring agent, and that such pearls can be identified by their color, fluorescence, spectra and trace elements (2006).
Choker
A necklace of uniform-sized pearls 35 to 40 cm (14 to 16 inches) long.4
CIBJO's definition covers strands of natural, cultured or imitation pearls (5.39).
Circled pearl
A pearl with one or more concentric rings or grooves around it.4 8
CIBJO also uses the French word cerclé (5.35, 5.40). GIA counts circled among eight basic pearl shapes.
Clam pearl
A natural pearl from a hard-shell clam, such as the quahog, Mercenaria mercenaria, or from a giant clam, such as Tridacna gigas.4
Clam pearls are non-nacreous (CIBJO 5.141). CIBJO's definition refers to CITES, the convention on trade in endangered species (5.41).
Coating (treatment)
An artificial layer of any substance spread over all or part of a pearl's surface, to protect it, color it, add luster or otherwise change how it looks.4
CIBJO 5.44. Its standards require coating to be disclosed when natural or cultured pearls are sold (4.4.2.2, 4.5.2.2).
Coin pearl
A trade name for coin-shaped, bead-cultured freshwater pearls.2 4
CIBJO notes that beads are often round but can be other shapes, such as coins (5.144), and its 2025 guide lists Coin among the trade names for beaded freshwater cultured pearls.
Collar length
A necklace 25 to 33 cm (10 to 13 inches) long, the shortest of CIBJO's standard lengths.4
CIBJO calls it a collar (5.45).
Composite cultured pearl
A product made of two or more separate parts or layers bonded together, at least one of which is a natural or cultured pearl.4
CIBJO also calls such products assembled (5.12, 5.13). A mabe is an assembled cultured blister (5.112).
Computed microtomography
An X-ray method that builds a three-dimensional model of a pearl's inside, used in difficult identifications and to measure nacre thickness and volume.11 12 13
GIA uses it on loose pearls that need more detailed analysis, and has used it to measure the nacre and bead of Akoya cultured pearls (2025) and for small pearls whose structure is hard to read (2018).
Conch pearl
A non-nacreous natural pearl from the queen conch and some other sea snails, usually with a flame-like surface pattern and a porcelain-like sheen.4
The pattern comes from calcium carbonate arranged in a crossed lamellar structure. CIBJO notes that conch pearls are also known as pink pearls, and its definition refers to CITES, the convention on trade in endangered species (5.48).
Conchiolin
The organic material that binds the mineral platelets of nacre together.4
CIBJO describes it as a mix of beta-chitin and glycoproteins (5.49), and elsewhere as a complex scleroprotein (5.126).
Coque de perle
A section cut from the curved, nacreous surface of a chambered nautilus shell and made into jewelry to resemble a large oval half pearl.4
CIBJO classes coques de perles as imitations of pearls (5.50).
Cortez cultured pearl
A trade name for bead-cultured pearls grown in the rainbow-lipped pearl oyster, Pteria sterna, in the Gulf of California, Mexico, also known as the Sea of Cortez.4
The oyster has been used since the 1990s for nacreous cultured blisters as well as beaded cultured pearls (CIBJO 5.51, 9.69).
Cristaria plicata
The cockscomb pearl mussel, the freshwater mussel originally used for pearl culture in both Japan and China.4
In Japan it is known as the Karasu mussel (CIBJO 9.16). Hyriopsis cumingii, the triangleshell mussel, has a thicker shell (9.31).
Cultured blister
A blister grown on purpose by placing a bead or other material against the inside of a shell, so that nacre forms over it and joins the shell's lining.4
After harvest it is cut from the shell with the material still inside (CIBJO 5.131). A cultured blister pearl is a cultured pearl that broke through the mantle or gonad and grew onto the shell (5.53).
Cultured conch pearl
A cultured pearl grown with human help inside a cultured pearl sac in the queen conch, Aliger gigas.4
CIBJO 5.56. It is a non-nacreous cultured pearl (5.140).
Cultured pearl
A pearl formed inside a living mollusk in a pearl sac that was started by people.4 7
The FTC's definition assumes a nucleus planted by people (16 CFR 23.19(b)); CIBJO's (5.55) also covers pearls grown without a bead. In the United States a cultured pearl may not be called just a "pearl" (16 CFR 23.20(b)).
Cut pearl
A natural or cultured pearl cut to give it a flat base, often in half or to three quarters.4
CIBJO's standards require cut cultured pearls to be described as half or three-quarter cut cultured pearls (5.58, 5.59, 4.5.2.1).
Cyst pearl
A natural pearl that forms in a pearl sac inside the mollusk, out of contact with its shell.4
CIBJO 5.60.
D
Dobo pearls
A commercial name for cultured pearls, usually from Pinctada maxima, traded and exported through Dobo in Indonesia.4
CIBJO 5.62.
Drilled
Describes a pearl with a hole that goes in at one point and comes out on the opposite side.4
CIBJO 5.64. Drilling is one of the normal procedures, which don't count as treatments (5.143).
Dyeing
A treatment that changes a pearl's color with a dye or stain.4 14
Dyeing and irradiation are the most common color treatments (GIA 2021). CIBJO's standards require dyeing to be disclosed when natural or cultured pearls are sold (4.4.2.2, 4.5.2.2).
E
Edison pearl
A trade name for large, near-round to round bead-cultured freshwater pearls from China.2 14
GIA describes Edison as the trade name of the Chinese company that developed and produces them (2021). CIBJO's 2025 guide lists it with Coin, Fireball, Ming and Soufflé among the trade names for beaded freshwater cultured pearls.
F
Faceted pearl
A pearl polished to give it many flat, convex or concave facets.4
CIBJO 5.67, 5.68. Faceting is one of the normal procedures (5.143).
Filling
A treatment that puts a substance into all or part of an empty space in a pearl.4
CIBJO 5.70. Fracture filling fills a crack, for example with glass, resin or oil, to make it less visible (5.74). Both must be disclosed (4.4.2.2, 4.5.2.2).
Flame structure
A flame-like pattern often seen on the surface of non-nacreous pearls, such as conch and melo pearls.1 4
In conch pearls the pattern comes from calcium carbonate arranged in a crossed lamellar structure (CIBJO 5.48). CIBJO also mentions it on some spiny oyster, or Spondylus, pearls (9.79).
Freshwater cultured pearl
A cultured pearl grown in a freshwater mussel, today mostly Hyriopsis cumingii in China.2 4 15
CIBJO requires the full term "freshwater cultured pearl" (4.5.1.2).
Freshwater natural pearl
A natural pearl from a bivalve that lives in fresh water, such as a river, lake or pond.4
CIBJO 5.78, 5.76. Scottish pearls, from the mussel Margaritifera margaritifera in Scotland, are one kind (5.178).
G
Gastropod
A snail, such as a conch or an abalone.4
CIBJO describes marine gastropods as univalve mollusks, with a single shell, that live in the sea (5.101, 5.116). Abalone and melo volutes are marine gastropods (9.1, 9.43), and conch pearls come from gastropods too (5.48).
Gonad
A mollusk's reproductive organ, where the bead and graft for saltwater bead-cultured pearls are usually placed.4 16
Gonad-grown cultured pearl
A cultured pearl grown in a mollusk's gonad, where the graft was placed.4
CIBJO 5.83, 5.86.
Graduated strand
A strand of pearls that change in size along its length, with the smallest often next to the clasp.4 17
SSEF reports say whether a necklace is regularly graduated or non-graduated, and give diameters for a graduated necklace's two smallest pearls, two intermediate pearls and the largest. CIBJO describes a graduated strand by the largest diameter of its largest pearl and the smallest diameter of its smallest (4.1.6.2).
Graft
A small piece of mantle tissue cut from one mollusk and inserted into another, usually of the same species, to start a cultured pearl sac.4
Grafts go into the mantle or the gonad, giving mantle-grown or gonad-grown cultured pearls (CIBJO 5.86).
Grafting
Placing a piece of mantle tissue from one nacre-producing mollusk into another, usually of the same species, to start a cultured pearl sac.4
The graft goes into the mantle or the gonad, giving mantle-grown or gonad-grown cultured pearls (CIBJO 5.86).
Grain (pearl weight)
A trade unit used to estimate the weight of natural pearls, equal to a quarter of a carat.4
One carat is 200 mg (CIBJO 5.33), so a grain is 50 mg.
H
Hatchery
A facility where young pearl oysters or mussels are bred, as an alternative to collecting them from the wild.9
Juveniles bred in hatcheries or collected as wild spat are grown on until they are big enough for pearl production (Zhu and others 2019).
Heating
A treatment that heats a pearl to a temperature that may change its appearance.4
CIBJO 5.96. Its standards require heating to be disclosed when cultured pearls are sold (4.5.2.2).
Hinge pearl
An irregular, usually elongated natural pearl found near the hinge of a bivalve's shell.4
In the United States the name has also been used for pieces of shell carved from the hinge of freshwater mussels to look like natural pearls (CIBJO 5.97).
Hollow pearl
A natural or cultured pearl with a large enclosed cavity.4
CIBJO 5.98, 5.99. Soufflé freshwater cultured pearls are usually hollow once drilled and cleaned out (5.184).
Hyriopsis cumingii
The triangleshell pearl mussel, native to China and Vietnam and now the main freshwater mussel used for pearl culture in China.4
Its nacre is pink to peach, and its natural and cultured pearls range from white to pink, lavender and deep rose (CIBJO 9.31, 9.81).
I
Imitation pearl
A manufactured product that only imitates the look of a natural or cultured pearl.4 7
US rules and CIBJO require a qualifier such as "imitation" (16 CFR 23.20(c); CIBJO 4.4.1.1.2).
Irradiation
A treatment that exposes pearls to radiation, controlled wholly or partly by people, usually to change their appearance.4 18
It has been used on freshwater cultured pearls since the 1960s, darkening their manganese-rich nacre, and in Akoya pearls it darkens the freshwater-shell bead inside (GIA 2024). CIBJO's standards require it to be disclosed when natural or cultured pearls are sold (4.4.2.2, 4.5.2.2).
K
Kan
A unit of cultured pearl weight equal to 1,000 momme, or 3.75 kilograms.4 16
CIBJO 5.103. Japan's cultured pearl output peaked in 1966 at 39,522 kan, or 148.2 tonnes (GIA 2007).
Keshi
A trade name for a small, usually baroque saltwater pearl that formed without a bead, today mostly a by-product of bead culturing.2 4 19 20
The name comes from the Japanese word for poppy seed (CIBJO 2025 guide). CIBJO says it should be qualified as natural or cultured (5.105); GIA and SSEF reports say non-bead or beadless cultured pearl instead.
Knotting
Tying a knot between each pearl on a strand, so the pearls don't rub against each other and you don't lose them all if the string breaks.8
GIA says experts recommend it (Pearl Buyer's Guide).
L
Laboratory report
A gem laboratory's written description of a pearl or strand, saying what it is and recording its features.5 17
A GIA report states whether pearls are natural or cultured, the water they grew in, the mollusk when it can be determined and any detectable treatments, and grades them on GIA's seven value factors (GIA 2026). SSEF's reports give each strand's length, clasp included, and its diameters.
Lagniappe cultured pearl
A cultured pearl that grows as a by-product of freshwater pearl culture in the United States.4
The word, said to come from New World Spanish and Quechua, is used in southern Louisiana for a little bonus (CIBJO 5.107). CIBJO also calls these bonus cultured pearls (5.30).
Liang
An imperial Chinese unit of weight equal to 250 carats, or 50 grams.4
CIBJO 5.108. One carat is 200 mg (5.33), so 250 carats make 50 g.
Luster
The quality and amount of light a pearl reflects from its surface and from just below it.4 6
GIA grades luster Excellent, Very Good, Good, Fair or Poor; CIBJO's scale has four steps, excellent, good, fair and poor (5.110).
Luster enhancement
Any treatment other than polishing that improves a pearl's luster, such as maeshori.4
CIBJO's standards require luster enhancements to be disclosed when cultured pearls are sold (5.111, 4.5.2.2).
M
Mabe
An assembled cultured blister, made by cutting a blister grown against the shell, removing its bead, filling the space and backing it with shell.4
The name comes from the mabe oyster, Pteria penguin, but is now used for assembled blisters from other mollusks too (CIBJO 5.112). Hankei is another name (5.14).
Maeshori
A multi-step chemical treatment, using heat or light, that temporarily improves a pearl's luster.4 14
Mantle
The body wall of a mollusk, whose outer surface secretes the shell.4
Pearl sacs grow from the mantle's outer layer of cells (CIBJO 5.160).
Mantle-grown cultured pearl
A cultured pearl grown in a mollusk's mantle, where the graft was placed.4
CIBJO 5.115, 5.86.
Margaritifera margaritifera
The freshwater pearl mussel of fast-flowing rivers and streams in Europe and North America, source of natural freshwater pearls such as Scottish pearls.4
It needs cool, clean, well-oxygenated soft water, and its larvae spend months on the gills of salmonid fish (CIBJO 9.41, 5.178). Its entry refers to CITES.
Matinee length
A necklace 50 to 60 cm (20 to 24 inches) long.4
CIBJO calls it a matinee (5.118).
Melo pearl
A non-nacreous natural pearl from a melo volute, a sea snail of the genus Melo.4
CIBJO 5.119. One species, Melo aethiopica, lives mainly in Indonesian waters, from Java to Papua New Guinea (9.43).
Methgal
A unit of weight equal to 4.5 grams.4
CIBJO 5.120.
Mollusk
An invertebrate animal of the phylum Mollusca, such as an oyster, mussel, clam or snail.4 9
CIBJO 5.121, 5.21, 5.101. Pearls are cultured mainly in marine pearl oysters and in freshwater pearl mussels (Zhu and others 2019).
Momme
A unit of cultured pearl weight equal to 3.75 grams, used mainly in the Japanese pearl trade.4
1,000 momme make one kan, or 3.75 kilograms (CIBJO 5.103). Also spelled monme.
Mother-of-pearl
The smooth, hard, iridescent nacre that lines the inside of some mollusk shells.4
Mussel pearl
A rare cream, purple or black nacreous natural pearl from the marine brown mussel, Modiolus philippinarum, fished as seafood in the Philippines and Mozambique.4
It reaches up to 9 mm across, and may also be found in other mussels of the family Mytilidae (CIBJO 5.125).
N
Nacre
The layered material, microscopic aragonite platelets bound by conchiolin, that makes up nacreous pearls and the shiny lining of their shells.4
This structure is what produces orient and overtone (CIBJO 5.126).
Nacre thickness
The thickness of the nacre over the bead of a beaded cultured pearl, usually given as an average in millimeters.4 6
It depends on how long the pearl was grown and can affect color, luster and durability, but thick nacre isn't necessarily good-quality nacre (CIBJO 5.127). A visible bead or a chalky look suggests thin nacre (GIA).
Nacre volume
The nacre's share of a bead-cultured pearl's volume, given as a percentage.4
CIBJO 5.128. Nacre thickness is the depth of nacre over the bead, usually given as an average in millimeters (5.127).
Natural pearl
A pearl that formed inside a mollusk without any human help.4 7
Under US rules and CIBJO, the word "pearl" alone means a natural pearl (16 CFR 23.20(a); CIBJO 4.4.1.1.2).
New World natural pearl
A natural pearl from the La Paz pearl oyster, Pinctada mazatlanica.4
Fisheries once gave plenty of naturally colored pearls, from light gray to black with pink, gold and green tones; the oyster now gives limited quantities of mabe (CIBJO 5.138).
Non-beaded cultured pearl
A cultured pearl grown without a bead, from mantle tissue alone.4 21
Most Chinese freshwater cultured pearls are grown this way (Japan Fisheries Agency).
Non-nacreous pearl
A pearl without a surface layer of nacre, such as a conch, melo, clam or scallop pearl.1 4
CIBJO's list of non-nacreous natural pearls also includes some pen pearls (5.141), and it defines non-nacreous cultured pearls too, grown in the queen conch (5.140).
Normal procedures
In CIBJO's standards, the handling a natural or cultured pearl can have without counting as treated, which is drilling, cutting, faceting, carving, polishing, buffing and cleaning.4
CIBJO 5.143. Anything more makes it a treated pearl (5.206). Cleaning doesn't include bleaching or maeshori (4.4.2.1, 4.5.2.1).
O
Oiling
A treatment that soaks a pearl's surface in warm oil to make cracks less visible.4
CIBJO says the process is called "decraqueler", and its standards require it to be disclosed (5.146, 4.4.2.2, 4.5.2.2).
Once-the-weight
A method of pricing natural pearls in which a pearl's weight in grains is squared and multiplied by a base price.4
Natural pearls are not simply priced at so much per grain, and the trade often shortens the phrase to "the once" (CIBJO 5.147).
Opera length
A necklace 70 to 90 cm (28 to 35 inches) long.4
CIBJO calls it an opera (5.148). A necklace longer than opera length is a sautoir (5.176).
Optical brightening
A treatment with chemicals that absorb ultraviolet and violet light and give it off again as blue fluorescence.4
CIBJO says these chemicals, optical brightening agents (OBAs), are not unusual in the cultured pearl industry and are sometimes applied routinely after harvest (5.149). Its standards require the treatment to be disclosed (4.5.2.2).
Orient
Soft rainbow colors that shimmer on or just below the surface of some nacreous pearls.4 6
CIBJO attributes it to interference and diffraction of light (5.151).
Oriental pearl
An old commercial name for some natural saltwater pearls.4 7
CIBJO allows it only for natural saltwater pearls, and never to denote a pearl's quality or appearance (5.152, 4.4.1.1.1). US rules limit it to pearls from saltwater mollusks with the distinctive appearance and type of pearls from the Persian Gulf, and forbid the word "Oriental" for cultured or imitation pearls (16 CFR 23.21(c)–(d)).
Overtone
A translucent secondary color lying over a pearl's bodycolor, usually pink, green or blue.4 6
P
Part-drilled
A pearl with a drill hole that goes in but doesn't come out the other side.4
Pearl doctor
A specialist who judges which layers to remove from a dull or blemished pearl to reveal a better pearl beneath.4
CIBJO 5.157.
Pearl essence
A coating that imitates the iridescence of nacre, spread over glass, plastic or shell beads to make imitation pearls.4 22 23
CIBJO's French term, essence d'orient, describes powdered fish scales in resin or another coating (5.66). Imitation pearls from the Spanish island of Majorca have been made by coating a glass bead with layers of an essence made from fish scales (GIA 1990).
Pearl oyster
A marine bivalve of the family Pteriidae, in the genus Pinctada or Pteria.4
CIBJO 5.158. The edible oysters belong to a different family, Ostreidae (5.154).
Pearl sac
The sac of cells, grown from mantle tissue, that lays down a pearl's layers.4
In a cultured pearl the sac grows from inserted mantle tissue or from damage during handling (CIBJO 5.54).
Peeling (skinning)
Removing the outer, loosely attached layers of nacre from a natural pearl to reveal a cleaner layer beneath.4
CIBJO 5.161. It is also called skinning (5.183), and it is not the same as working (5.161).
Pinctada fucata
The Akoya pearl oyster, used to culture Akoya pearls in Japan, China, Australia and elsewhere.4
It is known in Japan as Pinctada martensii and is sometimes treated as a subspecies of Pinctada imbricata; its natural range runs from Japan to China and Vietnam (CIBJO 9.3, 9.54).
Pinctada imbricata
The Atlantic pearl oyster of the western Atlantic, from Bermuda and Florida to northern South America.4
Venezuelan natural pearls come from it (CIBJO 5.207, 9.55).
Pinctada margaritifera
The black-lipped pearl oyster, the widest-ranging pearl oyster, used to culture Tahitian pearls in French Polynesia.4
Its natural pearls have been gathered in the Red Sea, the Indian Ocean, across the Indo-Pacific islands, in Mexico and in Okinawa, Japan; the variety cultured in French Polynesia is Pinctada margaritifera cumingii (CIBJO 9.11).
Pinctada maxima
The silver-lipped or gold-lipped pearl oyster, the largest pearl oyster, used for South Sea cultured pearls in Australia, Indonesia, Myanmar, the Philippines and elsewhere.4
Pearling fleets once dived for it for its large natural pearls and its mother-of-pearl (CIBJO 9.60). The gold-lipped form is a variety of the same species (9.26).
Pinctada mazatlanica
The La Paz or Panamic black-lipped pearl oyster of the eastern Pacific, from the Gulf of California to Peru.4
Its fisheries gave the naturally colored New World natural pearls, and it is now used for limited quantities of mabe and bead cultured pearls (CIBJO 9.61, 5.138).
Pinctada radiata
The Gulf or Ceylon pearl oyster, source of the natural pearls of the Arabian Gulf.4
It lives in the eastern Mediterranean, the Red Sea, the Persian Gulf and the Indian Ocean, and is sometimes considered a variety of Pinctada imbricata (CIBJO 9.62). Basra and Bahraini pearls come from it, and Bombay pearls mostly do (5.15, 5.17, 5.28).
Pinna pearl
A natural pearl, often orange or brown, from a pen shell, a marine bivalve of the genus Pinna or Atrina.4
It may be non-nacreous or nacreous, and some are silvery (CIBJO 5.167). CIBJO's entry for pen pearl points to this one (5.162).
Polishing
Rubbing a natural or cultured pearl to remove some surface blemishes and increase its luster.4
CIBJO 5.168. A normal procedure that needs no disclosure (5.143); a luster enhancement is any treatment other than polishing (5.111).
Princess length
A necklace 43 to 48 cm (17 to 19 inches) long.4
CIBJO calls it a princess (5.169).
Pteria penguin
The mabe or black-winged pearl oyster, which gave its name to mabe, the assembled cultured blister.4
CIBJO describes an ovate, fairly fragile shell with unequal valves and a characteristic extension of the hinge line (9.68, 5.112).
Pteria sterna
The rainbow-lipped pearl oyster of the eastern Pacific, from Baja California to Peru, used for Cortez cultured pearls.4
Its fisheries gave naturally colored pearls from light gray to dark purple, and since the 1990s it has been used for cultured blisters and beaded cultured pearls (CIBJO 9.69).
R
Real (genuine)
Genuine and not artificial.4 7
CIBJO 5.170, 5.81. US rules forbid "real," "genuine" and "precious" for imitation pearls (16 CFR 23.21(i)).
Restringing
Putting a strand's pearls on new string, since string stretches and weakens over the years.8 24
GIA advises restringing pearls that are worn often once a year (2015), and says a strand that shows too much string can easily be restrung (Pearl Buyer's Guide).
Rin-dama
A name for extra-small Akoya, 3 to 4 mm across.2
It is the smallest of the Akoya size classes in CIBJO's 2025 guide, where 5 mm pearls are small, 6 to 7 mm medium, and 8 mm or more large (p. 184).
Rope length
A necklace about 115 cm (45 inches) long or longer, the longest of CIBJO's standard lengths.4
CIBJO calls it a rope (5.171).
S
Saltwater pearl
A natural or cultured pearl from a mollusk that lives in salt water, in the sea, an ocean or a lagoon.4
CIBJO 5.172, 5.173, 5.174.
Sango cultured pearl
A trade name for a pink cultured pearl grown in Japan in the Akoya pearl oyster around a bead of pink coral.4
CIBJO counts it as an atypical bead cultured pearl (5.175), its name for one grown on a bead of anything other than the usual shell (5.18).
Sautoir
A pearl necklace longer than opera length, about 90 cm (36 inches).4
CIBJO's definition covers natural, cultured and imitation pearls (5.176).
Scallop pearl
A non-nacreous natural pearl from a scallop, whose surface is a patchwork of cells that gives it a distinctive sheen.4
Each cell is made of three smaller ones, and their arrangement produces the sheen. CIBJO notes that scallop pearls differ in surface and composition from conch and melo pearls (5.177).
Scottish pearls
Natural freshwater pearls from the mussel Margaritifera margaritifera in Scotland.4
CIBJO 5.178.
Seed pearl
A very small natural pearl, about 2 mm across or less.4 7
The FTC says about 2 mm or less (16 CFR 23.19(d)); CIBJO says generally under 2 mm and never more than 3 mm (5.179).
Soufflé freshwater cultured pearl
A baroque freshwater cultured pearl that grows around mud placed in an existing pearl sac after the first harvest; once drilled and cleaned out, it is usually hollow and very light for its size.2 4
CIBJO notes that they come from some Chinese mussels, and counts them as atypical bead cultured pearls (5.184).
South Sea cultured pearl
A cultured pearl from the large Pinctada maxima oyster, farmed mainly in Australia, Indonesia, the Philippines and Myanmar.4 7 15
US rules allow the name only for pearls from saltwater mollusks of the Pacific Ocean South Sea Islands, Australia or Southeast Asia (16 CFR 23.21(g)).
Spat
Larval saltwater mollusks that have settled on a hard surface to grow into adults.4 9
Freshwater larvae, called glochidia, instead attach to the gills of certain fish until their shells form (CIBJO 5.189). Pearl farms raise spat in hatcheries or catch wild larvae as they settle on collectors placed in the water (Zhu and others 2019).
Special care
Extra care that some natural or cultured pearls need to keep their appearance, for example after a treatment.4
CIBJO 5.190. On trade documents the code SC marks it (4.3.2), and a treatment that isn't permanent must be declared as needing special care before a sale closes (4.2.4).
Spiny pearl
A non-nacreous pearl, often layered and white, yellow, orange, brown or purple, from a thorny or spiny oyster of the genus Spondylus.4
Some show a bluish iridescence or flame structure on the surface, and the trade also calls them Spondylus pearls (CIBJO 9.79, 9.80). Spondylus shell was used for decoration and coinage in pre-Columbian civilizations (9.80).
Surface quality
How free a pearl's surface is of blemishes such as abrasions, flattened areas or ridges, one of GIA's value factors.6
Numerous or severe blemishes can affect a pearl's durability and severely depress its value, while a few minor ones, or ones hidden by a drill hole or mounting, matter less (GIA).
Synthetic (pearls)
A word that US rules forbid for cultured or imitation pearls.7
16 CFR 23.21(j). In the FTC's definitions a cultured pearl is coated with nacre by a mollusk, and an imitation pearl is a manufactured product (16 CFR 23.19).
T
Tahitian cultured pearl
A naturally colored cultured pearl from the black-lipped pearl oyster, grown in French Polynesia.4 15 25
Sometimes called black pearls, though GIA describes a wide color range, from gray to black or brown.
Tawash
An Arabian name for a pearl merchant.4
CIBJO 5.199.
Tinting
A treatment that makes a subtle change to a pearl's color or appearance, often linked with bleaching.4
CIBJO's standards require tinting to be disclosed (5.203, 4.4.2.2, 4.5.2.2).
Tooth test
Feeling a pearl's surface against the teeth, a first check against imitations; in a GIA study the cultured pearls felt gritty and the imitations smooth.23
GIA found it one of four conclusive tests for separating a widely sold imitation from cultured pearls, with refractive index, magnification and X-radiography (1990). Natural pearls share most surface characteristics with cultured pearls, so it can't tell those two apart.
Trade codes
Letter codes the trade uses on invoices and labels to show how a pearl has been treated, such as BW for bleached and waxed.4
CIBJO 5.205, 4.3.2. They are for use within the industry only, not with the public (4.3).
Treated pearl
A natural or cultured pearl altered beyond the normal procedures, to change its color, composition, appearance or durability.4
CIBJO 5.206. Its standards require each treatment to be named when the pearl is sold (4.4.2.2, 4.5.2.2).
Tridacna gigas
The giant clam of the Indo-Pacific, the largest and heaviest known mollusk, whose pearls are porcelain-like and white.4
Its two valves can weigh about 225 kg (CIBJO 9.82). Its entry refers to CITES.
U
Uniform strand
A strand of pearls that are all about the same size.4 17
SSEF reports call such necklaces non-graduated. CIBJO describes a uniform strand, like a graduated one, by the largest diameter of its largest pearl and the smallest diameter of its smallest (4.1.6.3).
V
Value factors
The qualities used to judge a pearl's value; GIA's seven are size, shape, color, luster, surface quality, nacre quality and, for jewelry with two or more pearls, matching.1 6
GIA says luster might be the most important of them. The classification system set out in GIA's journal applies to nacreous pearls of the three main saltwater types, Akoya, South Sea and Tahitian (2021).
Venezuelan pearl
A natural pearl from the Atlantic pearl oyster, Pinctada imbricata, of the western Atlantic.4
CIBJO notes that the oyster was the source of Columbus's pearls (5.207).
W
Waxing
A treatment that applies a colorless wax or a similar product to, or near, a pearl's surface.4
CIBJO's standards require waxing to be disclosed (5.209, 4.4.2.2, 4.5.2.2).
Worked pearl
A pearl, usually natural, whose blemishes have been removed or whose shape has been changed, lightly or heavily.4
Light working removes a blister pearl's shell attachment; heavy working makes an out-of-round pearl round, most often a non-nacreous one. CIBJO says working must be stated in any document describing the pearl (5.211).
X
X-radiography
Imaging a pearl with X-rays to see inside it, for example to show a shell bead and the nacre over it.11 26
X-ray radiography remains an essential method for telling natural from cultured pearls (GIA 2024). GIA uses real-time microradiography to measure nacre thickness when the nacre looks thin or a client asks.
X-ray luminescence
The glow some pearls give off under X-rays, used to tell freshwater pearls from saltwater ones.27
Freshwater pearls, richer in manganese, glow yellow-green, while saltwater pearls without a bead stay inert; a saltwater cultured pearl can glow too, from its freshwater-shell bead under thin nacre (Karampelas and others 2019).
References#
- Joyce Wing Yan Ho and Sally Chan Shih (2021). Pearl Classification: The GIA 7 Pearl Value Factors. Source · Archived copy (accessed 2026-10-26)
- CIBJO Pearl Commission (2025). CIBJO Guides Describing and Classifying Natural and Cultured Pearls, the Producing Molluscs & Responsible Pearling. Source · Archived copy (accessed 2026-10-25)
- Gemological Institute of America (GIA), FAQ. What's AAA-quality tanzanite?. Source · Archived copy (accessed 2026-10-26)
- CIBJO, The World Jewellery Confederation, Pearl Commission (2026). The CIBJO Pearl Book (Pearl Blue Book) 2026. Source · Archived copy (accessed 2026-10-25)
- Phoebe Shang (2026). Freshwater Akoyas – A Trending Misnomer for Certain Freshwater Pearls. Source · Archived copy (accessed 2026-10-25)
- Gemological Institute of America (GIA), Gem Encyclopedia. Pearl Quality Factors. Source · Archived copy (accessed 2026-10-25)
- U.S. Federal Trade Commission (Electronic Code of Federal Regulations). 16 CFR Part 23, Guides for the Jewelry, Precious Metals, and Pewter Industries. Source · Archived copy (accessed 2026-10-25)
- Gemological Institute of America (GIA), Gem Encyclopedia. Pearl Buyer's Guide. Source · Archived copy (accessed 2026-10-25)
- Changbo Zhu, Paul C. Southgate and Ting Li (2019). Production of Pearls. Source · DOI 10.1007/978-3-319-96776-9_5 · Archived copy (accessed 2026-10-25)
- Wuyi Wang, Kenneth Scarratt, Akira Hyatt, Andy Hsi-Tien Shen and Matthew Hall (2006). Identification of "Chocolate Pearls" Treated by Ballerina Pearl Co.. Source · DOI 10.5741/GEMS.42.4.222 · Archived copy (accessed 2026-10-25)
- Gemological Institute of America (GIA), Analysis & Grading. How GIA Identifies and Classifies Pearls. Source · Archived copy (accessed 2026-10-25)
- Kwanreun Lawanwong, Ravenya Atchalak and Emiko Yazawa (2025). Exceptional Nacre Thickness of Hybrid Akoya Bead Cultured Pearls. Source · Archived copy (accessed 2026-10-25)
- Areeya Manustrong (2018). Very Small Akoya Cultured Pearls. Source · Archived copy (accessed 2026-10-25)
- Chunhui Zhou and others (2021). Detection of Color Treatment and Optical Brightening in Chinese Freshwater "Edison" Pearls. Source · DOI 10.5741/GEMS.57.2.124 · Archived copy (accessed 2026-10-25)
- Gemological Institute of America (GIA), Gem Encyclopedia. Pearl Description. Source · Archived copy (accessed 2026-10-25)
- Russell Shor (2007). From Single Source to Global Free Market: The Transformation of the Cultured Pearl Industry. Source · DOI 10.5741/GEMS.43.3.200 · Archived copy (accessed 2026-10-25)
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- Artitaya Homkrajae, Nanthaporn Nilpetploy, Areeya Manustrong, Nicholas Sturman, Kwanreun Lawanwong and Promlikit Kessrapong (2021). Internal Structures of Known Pinctada maxima Pearls: Cultured Pearls from Operated Marine Mollusks. Source · DOI 10.5741/GEMS.57.3.186 · Archived copy (accessed 2026-10-25)
- Michael S. Krzemnicki (2010). Trade Alert: "Keshi" cultured pearls are entering the natural pearl trade. Source · Archived copy (accessed 2026-10-25)
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- Karan Rajguru, Anukul Belanke and Abeer Al-Alawi (2025). Imitation Seed Pearl with Blue X-Ray Fluorescence. Source · Archived copy (accessed 2026-10-26)
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- Written by
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- Unique Pearl, a pearl jeweler
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@misc{lap-glossary, title = {Pearl Glossary}, author = {{Learn About Pearls editors}}, year = {2026}, howpublished = {\url{https://learnaboutpearls.com/glossary/}}, note = {Learn About Pearls, published by Unique Pearl}}
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