.Abalone Pearl
A natural pearl, usually coloured, found in gastropod molluscs of the Haliotis genus in the Pacific, Atlantic and Indian Ocean.
.Adductor Muscle
The muscle attached to both valves of a bivalve that causes the shell to close when it contracts (Mikkelsen, 2003).
.Akoya Pearl
A pearl produced in Pinctada fucata (martensii).
Cultivation of aquatic animals or plants in water.
.Arabian Gulf
An area in Southwest Asia that is an extension of the Indian Ocean located between Iran and the Arabian Peninsula.
.Arabian Gulf Pearls
Natural pearls produced from the Pinctada radiata.
A crystallised form of calcium carbonate found in pearl nacre and mother of pearl.
A ring like coral island and reef that nearly or entirely encloses a lagoon.
Trade term for Tahitian cultured pearls with a dark greyish purple body colour.
.Bahraini Pearl
A natural pearl from Bahraini waters in the Arabian gulf produced from the Pinctada radiata.
An irregularly shaped natural or cultured pearl. Baroque was originally a French adjective used to describe objects or pearls that were not symmetrical in shape (Mikkelsen, 2003).
.Basra Pearl
A natural pearl from the Arabian gulf produced from the Pinctada radiata.
.Bead for Cultured Pearls
Bead for cultured pearls A sphere (usually) or other shape (occasionally) originally formed by cutting and polishing a nacreous shell used to accommodate the nacre secreted from a cultured pearl sac. The bead eventually forms the centre of a beaded cultured pearl. Note: Atypically, beads formed from natural or cultured pearls of various types or other materials may be used, however, in such circumstances the product shall be described as containing an atypical bead or the type of bead shall be named, e.g., an ‘atypical bead cultured pearl’, a ‘turquoise bead cultured pearl’.
.Bead Nucleation
Insertion of a bead and a piece of mantle tissue into a mollusc to induce it to form a cultured pearl. Also known as Seeding and Grafting.
A member of the molluscan class Bivalvia, having a two-part shell, e.g., clam, oyster, mussel and scallop (Mikkelsen, 2003).
.Biwa Cultured Pearl
A freshwater non-beaded cultured pearl produced from grafting alone, in Lake Biwa, Japan, using the freshwater bivalve mollusc Hyriopsis schlegeli.
.Black-Lipped Pearl Oyster
A descriptive term for the mollusc that produces Tahitian pearls (Pinctada margaritifera cumingii). The inside edges of the P.margaritifera shell and the edges, or lips of the mantle tissue are black.
To remove, lighten (make whiter) or alter the colour of a pearl (e.g., from black to brown/bronze) by means of chemical and/or physical agents or light.
.Blister Cultured Pearl
A cultured pearl that has perforated the mantle of the mollusc and has adhered, through layers of nacreous or non-nacreous secretions applied by the mollusc, to the inner wall of the shell. The layers of nacreous or non-nacreous material subsequently formed are continuous with those of the inner wall of the shell. They are round or irregular in shape and the base of the blister cultured pearl may be worked.
.Blister Pearl
Dome shaped cultured pearl formed around a nucleus cemented against the inside of a mollusc’s shell.
.Bombay Pearls
Commercial name for natural pearls chiefly from Pinctada radiata fished in the Arabian Gulf but including pearls from other locations and species traded through Bombay, India.
.Bottom System
Mollusc-holding net panels attached to lines stretched between posts secured to the ocean floor.
Molluscs reserved especially for breeding purposes.
Removing organic residues from the surfaces of natural and cultured pearls following harvest.
.Button-Shaped Pearl
A symmetrical domed-shape pearl with or without a flattish bottom.
Sticky threads grown by a saltwater mollusc and used to attach itself to a fixed surface. This is the same material as the ’beard‘ of a mussel.
.Calcareous Concretion
A non-nacreous natural pearl such as those formed inside clams.
Calcium carbonate with a non-lustrous crystal structure, unlike aragonite.
Unit of weight (mass 5.98), equal to one fifth of a gram (200 milligrams) or 4 grains.
.Ceylon Pearl Oyster
Pinctada radiata, the most prolific pearl oyster native to the Gulf of Mannar, the Persian Gulf, and the Red Sea.
A strand of uniform sized natural pearls, cultured pearls or imitation pearls measuring 35-40cm (14 to 16 inches) in length.
.Circle Pearl
A pearl with one of more grooved or ridged rings visible around its circumference.
A term used in the industry when referring to the thickness of a pearl’s nacre.
A strand of pearls, cultured pearls or imitation pearls measuring 25-33cm (10 to 13 inches) in length.
Colour has three attributes: hue, tone, and saturation. Hue is the basic impression of colour—yellow, green, blue, etc. Tone is the relative impression of lightness or darkness of the colour. Saturation is the strength or intensity of the colour. In general the colour of nacreous natural and cultured pearls may be described in terms of a combination of body colour, overtone and orient. Nacreous natural pearls from the Arabian Gulf have a wide selection of colours that have traditional and distinctive trade names; white (Abyadh), dull white (Basali), black (Aswad), cream with a reddish hue (Nabati), white with a pinkish hue (Mushayer), whitish-blue or whitish-grey (Singbassi), white or cream with a bluish hue (Samawi), white with strong iridescent colours (Gallabi), white or cream with a strong green hue (Akhthar), glassy white or whitish-blue with high lustre (Alzujaji), rose pink (Wardi), light yellow (Ashgar), cream (Keremi).
The organic protein structure in nacre that surrounds the aragonite platelets.
.Cultured Pearl
A pearl that forms as the result of an irritant that is manually introduced into the oyster.
.Donor Tissue
Small piece of mantle tissue cut from a donor mollusc and implanted in a host mollusc with or without a bead. This is also known as ‘saibo‘ from the Japanese meaning “small cell”.
Any colour caused artificially by the application of a dye to pearls.
A removable pendant that can be added to necklace or strand to provide an alternative style.
.Epithelial Cells
In a mollusc, the epithelial cells of the mantle that secrete the shell, forming the outermost layer, including the nacre.
A substance that occupies a whole or part of a void in a low quality pearl.
Light emitted by some materials when they are exposed to high-energy sources such as UV light, x-rays or lasers.
.Freshwater Cultured Pearl
Cultured pearls produced in molluscs (mussels) in freshwater, e.g., Hyriopsis schlegelii, Hyriopsis cumingii. (Mikkelsen, 2003, Sweeny, 1982, Jobbins, 1993, Hänni, 2000, Scarratt, 2000, Akamatsu, 2001).
.Freshwater Mussel
Generic term used to describe the various species of bivalve freshwater molluscs that produces the majority freshwater pearls.
.Full Drilling
Drilling a hole all the way through a cultured pearl. Sometimes called a drilled through.
Class of single-shell molluscs that include land and sea snails.
The reproductive tissues that produce eggs in females and sperm in males.
.Graduated Strand
A necklace with the largest pearl in the centre and gradually smaller pearls approaching the clasp.
A piece of epithelium tissue cut from the mantle of a nacre-producing mollusc that is inserted into the body of another nacre producing mollusc, (usually of the same species), to initiate the growth of a cultured pearl sac and a cultured pearl.
The action of introducing tissue cut from the mantle of a nacre-producing mollusc into the body of another nacre-producing mollusc (usually of the same species) to initiate the growth of a cultured pearl sac and a cultured pearl. Grafting can be done into the recipient oyster‘s mantle or gonad – mantle-grown cultured pearls or gonad-grown cultured pearls.
0.25 of one carat (ct) (0.25ct, equivalent to 0.05 gram or 50 milligrams).
.Gulf Pearl
A natural pearl from the Arabian Gulf produced from the Pinctada radiata.
.Half Drilling
Drilling a hole that goes halfway through a cultured pearl.
A number of similar pearl strands bundled together.
Japanese trade name for cultured blister pearl.
Facility where pearl-bearing molluscs are reared in tanks.
.Hatchery Spawning
Stimulation of spawning of broodstock by chemical or environmental manipulation.
First impression of a colour; the basic colour of an object.
A natural or manmade material that simulates a gem.
Arising from, or composed of, non-living matter.
Exposing pearls or cultured pearls to radiation to enhance their appearance.
A unit of pearl weight equal to 1,000 momme or 3.75 kilograms.
A seedless pearl formed as a result of human intervention.
.La Paz Pearl Oyster
Pinctada mazatlanica from the eastern Pacific Ocean, presently cultured in the Gulf of California for blister and cultured pearls.
.La Peregrina
A magnificent natural pearl discovered in Central America in the sixteenth century, whose owners included Josephine and Elizabeth Taylor.
.Land-Based Farm
Pearl farm with personnel and equipment quartered on land.
Free swimming stage starting 16-20 hours post fertilisation and lasting for 14-20 days.
.Long-Line Systems
Mollusc-holding net panels hanging from floating horizontal lines.
The reflective quality or brilliance of the surface of the pearl’s nacre.
A assembly composed of a nacre dome, filler, and a mother-of-pearl backing.
.Maeshori Treatment
A multi-part chemical treatment that temporarily enhances lustre.
The organ that lies adjacent to the mollusc’s shell, encloses its soft body, and contains the epithelial cells that form the shell.
A strand of pearls, cultured pearls or imitation pearls measuring 50-60cm (20 to 24 inches) in length.
.Melo Pearl
A natural non nacreous pearl found in species of molluscs ranging from the South China Sea, south and west to Singapore and the Andaman Sea.
Soft bodied animal belonging to the phylum Mollusca. Includes shellfish, snails, squid and octopus.
An ancient Japanese unit of weight, used in the cultured pearl industry, equal to 3.75 grams (0.13 oz.). One momme is the approximate weight of a round pearl measuring 13.5mm.
.Mortality Rate
The percentage of pearl shell mortality on a pearl farm in a given period.
The nacreous layer inside the shell of some species of mollusc.
The natural substance produced by molluscs to make pearls and mother-of-pearl. Nacre is composed of calcium carbonate (in the form of the mineral aragonite) and conchiolin.
.Natural Pearl
A pearl formed without human assistance.
.Natural Spawning
Process of mollusc reproduction in the wild.
.Net Panel
A metal frame and mesh structure used to store, house and transport molluscs.

Implanting a piece of mantle tissue with or without a bead nucleus in a host mollusc to induce the development of a cultured pearl.
A highly skilled worker who implants bead nuclei and mantle tissue pieces or only mantle tissue pieces in molluscs. Sometimes known as a ‘grafter’. Commonly known as ‘technician’, ‘grafter’ or ‘seeder’.
A bead that is implanted to encourage the formation of a cultured pearl, traditionally made from freshwater mussel shell.
A strand of pearls measuring 70-90cm (28 to 35 inches) in length.
Once living, or produced by a living organism (plant or animal). Organic gems include pearl, amber, jet, ivory and coral.
The effect known as Orient refers to the unique play of colours on a pearl’s surface. It is a characteristic common to saltwater pearls but is not usually found in freshwater pearls. It should not be confused with the colour of the pearl which is determined by the colour of the shell in which the pearl formed. Pearls can be artificially coloured or bleached but orient cannot be replicated. Orient is also known as ‘overtones’ in dark coloured pearls.
.Oriental Pearl
Old commercial name for some natural saltwater pearls.
The presence of an additional colour on a pearl or pearl product, usually pink, gold, green, or blue.
Bivalve molluscs of the family Ostreidae.
Trade term for a Tahitian cultured pearl with dark green-grey to blue-grey body colour with a pink to purple overtone.
.Pearl Growth-Period
Time between the formation of the pearl sac and the harvest.
.Pearl Oyster
Marine bivalves classified in the family Pteriidae and the genera Pinctada and Pteria, e.g., Pinctada maxima, Pinctada margaritifera, Pinctada mazatlanica, Pinctada fucata (martensii), Pinctada imbricata, Pinctada radiata, Pinctada maculata, Pteria penguin, and Pteria sterna. Chinese freshwater pearls are produced in freshwater mussels, not pearl oysters.
.Pearl Polishing
A technique applied to pearls and cultured pearls to remove some surface blemishes and increase lustre.
.Pearl Sac
Tissue arising from transplanted mantle epithelium that encloses an implanted bead nucleus, and secretes nacre to form a cultured pearl.
A technique used to remove layers of nacre from a pearl to reveal higher quality nacre beneath. Can also be referred to as skinning.
.Pinctada Fucata
Pinctada fucata is the Akoya pearl oyster, known in Japan as Pinctada martensii. It is sometimes considered a subspecies of Pinctada imbricata. The shell is of a medium size and is rather inflated and fragile. The exterior is rough and is covered with layers of greyish purple lamellae which extend over the margins. The byssal notch lies below a small winged projection of the hinge line. Its habitat ranges from Japan to China and Vietnam (Wye, 1991, Landman, 2001).
.Pinctada Imbricata
Pinctada imbricata or the Atlantic Pearl Oyster, ranges naturally in the western Atlantic from Bermuda and Florida to northern South America. It is the source of Venezuelan pearls and also of Columbus‘s pearls (Mikkelsen, 2003).
.Pinctada Margaritifera
a large oyster that has equal compressed valves with a rich silver grey nacreous interior edged with greyish black. The exterior is formed from concentric layers of flaky green and grey lamellae. The source of natural and cultured, naturally coloured, black pearls from French Polynesia, the Cook Islands, Okinawa and other South Sea islands (Wye, 1991).
.Pinctada Martensii
Also referred to as Marten’s Pearl Oyster, the shell is of a medium size and is rather inflated and fragile. The exterior is rough and is covered with layers of greyish purple lamellae which extend over the margins. The byssal notch lies below a small winged projection of the hinge line. Its habitat ranges from Japan to China and Vietnam (Wye, 1991).
.Pinctada Maxima
This silver or golden lipped pearl oyster is the largest of all pearl oysters. Traditional South Sea pearling fleets dived for this pearl oyster in the quest for valuable large natural pearls, and the lucrative mother-of-pearl industry. Today, it is used extensively to produce cultured South Sea pearls in Australia, Indonesia, and the South Seas.
.Pinctada Mazatlanica
Pinctada mazatlanica (Hanley, 1855), the La Paz Pearl Oyster, or the Panamic Black-Lipped Pearl Oyster. A medium sized oyster (18 cm) with equally compressed valves with a rich silver grey nacreous interior edged with a green or golden sheen. The exterior is formed from concentric layers of flaky light-brown and green lamellae. Habitat ranges from inside the Gulf of California (also known as the Sea of Cortez), to Peru. Fisheries give abundant supplies of naturally coloured pearls, from light-grey to black, with many intermediate tones of pink, gold and green. This species was the first one to be used farmed commercially for the production of natural pearls in La Paz, Baja California Sur, Mexico. (Hurwit, K. 2000, Gomelsky,V. 2001, McLaurin, D. 2002, McLaurin, D. & E. Arizmendi, 2002).
.Pinctada Radiata
Pinctada radiata (Leache, 1814), or the Ceylon Pearl Oyster, is sometimes considered a variety of Pinctada imbricata. Its habitat ranges through the eastern Mediterranean, Red Sea, Persian Gulf and the Indian Ocean.
Trade term for Tahitian cultured pearls with a yellowish green to greenish yellow body colour.
Microscopic organisms used as food by molluscs and other aquatic animals.
Organic compounds in mollusc shells that researchers believe influence pearl colour, particularly yellow.
A strand of natural, cultured or imitation pearls measuring 43-48cm (17 to 19 inches) in length.
.Red Tide
An overabundance of phytoplankton that may be detrimental to molluscs and other sea life.
.Refractive Index (RI)
A measure of the change in the speed and angle of light as it passes from one material to another.
A strand of pearls, cultured pearls or imitation pearls measuring about 115cm (45 inches) and longer in length.
Pink overtone on a pearl.
.Sea-Based Farm
Pearl farm with quarters on a boat or pontoon.
.Seed Pearl
A small salt or freshwater natural pearl which is generally under two millimetres in diameter.
.South Sea
An area of the Pacific and the Indian Oceans (including the Indian Ocean) between Myanmar and Northern Australia and inclusive of Indonesia and the Philippines; the habitat of the Pinctada maxima pearl oyster. Tahitian pearls are not South Sea pearls.
Juvenile bivalve molluscs.
.Specific Gravity (SG)
Weight of a material per cubic centimetre.
.Sustainable Yield
The rate at which wild stocks can be taken while maintaining a stable and healthy population.
A man-made gem with essentially the same properties as a natural gem.
.Tahitian Cultured Pearl
A naturally coloured cultured pearl resulting from grafting and breeding in a natural environment, in French Polynesia, of the pearl oyster Pinctada margaritifera var. cumingii. It results from the secretion of nacre by a grafted cultured pearl sac (piece of epithelium of the mantle collected from the donor oyster from French Polynesia) around a bead inserted in the gonad of this pearl oyster.
A treatment which causes a subtle change in colour and/or appearance.
.Tissue Nucleation
Insertion of a piece of mantle tissue into a mollusc to induce it to form a cultured pearl with no bead nucleus.
Degree of darkness or lightness of a colour.
Natural Pearls: the weight of natural pearls is traditionally expressed in grains or carats. Cultured Pearls: the weight of cultured pearls is traditionally expressed in momme or carats. (1 momme = 3.75 grams; 100 grains = 1.73 momme; 57.8 grains = 1 momme; 1000 momme = 1 kan = 3.75 kilograms; ¼ of one carat = 0.05 gram/50 milligrams).
Significantly remove layers of nacreous or non-nacreous material from a pearl, usually to remove blemishes and/or to reshape a pearl, especially blister pearls. (Not commonly applied to cultured pearls.)
An imaging technique that uses X-rays to reveal an object’s internal structure.