What is the Pearl?
Pearls, natural or cultured, are formed when a mollusk produces layers of nacre (pronounced NAY-Kur) around some type of irritant inside its shell. In natural pearls, the irritant may be another organism from the water. In cultured pearls, a mother-of-pearl bead or a piece of tissue is inserted (by man) into the mollusk to start the process.
For both, the quality of the nacre dictates the quality of the luster, or shine of the pearl, which is very important to its beauty and its value. The surface of the pearl should be smooth and free of marks while the overall shape could be round, oval, pear-shaped, or even misshapen. Misshapen pearls are called baroque pearls.
While shopping for pearls, there are various lengths available:
- A collar fits directly against the throat
- A choker rests at the base of the neck
- The princess length reaches near the collarbone
- A matinee length is usually 20-24 inches
- The Opera length is 30-36 inches
- The longest length, known as a rope refers to all strands longer than 36 inches
· Necklaces can also be classified as uniform (where all pearls are about the same size) or graduated (pearls change uniformly from ends to center).
Physical Properties
The unique luster of pearls depends upon the reflection, refraction, and diffraction of light from the translucent layers. The thinner and more numerous the layers in the pearl, the finer the luster. The iridescence that pearls display is caused by the overlapping of successive layers, which breaks up light falling on the surface. In addition, pearls (especially cultured freshwater pearls) can be dyed yellow, green, blue, brown, pink, purple, or black. The very best pearls have a metallic mirror-like luster.
Because pearls are made primarily of calcium carbonate, they can be dissolved in vinegar. Calcium carbonate is susceptible to even a weak acid solution because the crystals react with the acetic acid in the vinegar to form calcium acetate and carbon dioxide.
Necklaces can also be classified as uniform (where all pearls are about the same size) or graduated (pearls change uniformly from ends to center).
Natural Pearls
Natural pearls are extremely rare. Historically, many were found in the Persian Gulf; unfortunately, today, most have already been harvested. You may be able to purchase small, natural pearls, but they will be costly.
Cultured Pearls
Cultured pearls are grown in pearl farms. The mollusks are raised until they are old enough to accept the mother-of-pearl bead nucleus. Through a delicate surgical procedure, the technician implants the bead, and then the mollusks are returned to the water and cared for while the pearl forms.
Not all produce a pearl; and not all the pearls are high quality. Over 10,000 pearls may be sorted before a 16” single strand of beautifully matched pearls is assembled.
Pearls can be found in saltwater and in freshwater. There are also different types of mollusks that produce very different looking pearls.
Saltwater pearls
Saltwater pearls include the Akoya cultured pearls grown in Japanese and Chinese waters. They range in size from 2mm (tiny) to 10mm (rare) and are usually white or cream in color and round in shape.
Australia, Indonesia, and The Philippines produce the South Sea pearl – the largest of all the pearls. They range in size from 9mm to 20mm and can be naturally white, cream, or golden in color.
Tahitian pearls are interestingly not exclusively from Tahiti – they’re grown in several of the islands of French Polynesia, including Tahiti. Their typical sizes range from 8mm to 16mm. These naturally colored pearls are collectively called black pearls, but their colors include gray, blue, green, and purple.
Freshwater Pearls
These pearls are grown in freshwater lakes, rivers, and ponds, predominately in China. Although many are white and resemble the Akoya cultured pearls in shape and size, they can also be produced in various shapes and in an array of pastel colors.
Many freshwater pearls don’t have a bead nucleus — only a piece of tissue — resulting in a pearl with thicker nacre than the Akoya.
Imitation Pearls
Imitation pearls are usually a coated glass bead. Most have a high luster, but not the depth of luster seen on high-quality cultured pearls.
It's possible to separate an imitation from a cultured or natural pearl. It can be a challenge, though, to determine if the pearl is cultured or natural. And, many pearls undergo treatments to either enhance their luster or alter their color.
Since this treatment affects their value, you will want to obtain the educated advice of a top jeweler, such as the certified gemologists of the American Gem Society.
Learn more about precious metals or diamonds.
Natural pearls are extremely rare. Historically, many were found in the Persian Gulf; unfortunately, today, most have already been harvested. You may be able to purchase small, natural pearls, but they will be costly.
Definition
All shelled mollusks can, by natural processes, produce some kind of "pearl" when an irritating the microscopic object becomes trapped within its mantle folds, but the great majority of these "pearls" are not valued as gemstones. Nacreous pearls, the best-known and most commercially significant, are primarily produced by two groups of molluscan bivalves or clams. A nacreous pearl is made from layers of nacre, by the same living process as is used in the secretion of the mother of pearl which lines the shell.
Natural (or wild) pearls, formed without human intervention, are very rare. Many hundreds of pearl oysters or mussels must be gathered and opened, and thus killed, to find even one wild pearl; for many centuries, this was the only way pearls were obtained, and why pearls fetched such extraordinary prices in the past. Cultured pearls are formed in pearl farms, using human intervention as well as natural processes.
One family of nacreous pearl bivalves – the pearl oyster – lives in the sea, while the other – a very different group of bivalves – lives in freshwater; these are the river mussels such as the freshwater pearl mussel. Saltwater pearls can grow in several species of marine pearl oysters in the family Pteriidae. Freshwater pearls grow within certain (but by no means all) species of freshwater mussels in the order Unionidae, the families Unionidae and Margaritiferidae.
Peral is the Organic Gems
Pearls are made of a kind of material made by mollusks, like oysters. Pearls are small and often white but sometimes in pale colors or even black. They are often round, but sometimes half-round, oval, or in different shapes. Pearls are often used for jewelry. The pearl is the birthstone for the month of June.
Although most gemstones are mineral materials, a number of organic materials are also considered to be gemstones. The most common of these are pearl, bone, amber, coral, jet, and ivory. These are materials, produced by organisms, that have been cut into gems and other ornamental objects.
There are also organic materials that have been mineralized (replaced and infilled by chalcedony, opal, calcite, aragonite, pyrite, or other mineral material). Although the material itself is not organic, it does preserve an organic structure. Examples include petrified wood, fossil coral, dinosaur bone, and other fossilized organisms or parts of organisms.
How a natural pearl is formed
A natural pearl is formed when nacre-producing cells are displaced from the mantle tissue of an oyster. These cells are genetically programmed to produce nacre, the substance that lines the inner sides of an oyster's shell. When the cells become displaced, often by a boring parasite or damage to the outer shell, they continue to do what they are programmed to do -- produce nacre and form a pearl.
They can be very tiny (as tiny as a peppercorn) or quite big (as big as a human's fist). The world's largest pearl, found in 1934 and called the Pearl of Lao-tze, is about the size of a basketball.
Value of a natural pearl
Fine quality natural pearls are very rare jewels. Their values are determined similarly to those of other precious gems, according to size, shape, color, quality of surface, orient, and luster.
Single natural pearls are often sold as collectors' items or set as centerpieces in unique jewelry. Very few matched strands of natural pearls exist, and those that do often sell for hundreds of thousands of dollars. (In 1917, jeweler Pierre Cartier purchased the Fifth Avenue mansion that is now the New York Cartier store in exchange for a matched double strand of natural pearls Cartier had been collecting for years; at the time, it was valued at US$1 million.
The introduction and advance of the cultured pearl hit the pearl industry hard. Pearl dealers publicly disputed the authenticity of these new cultured products, and left many consumers uneasy and confused about their much lower prices. Essentially, the controversy damaged the images of both natural and cultured pearls. By the 1950s, when a significant number of women in developed countries could afford their own cultured pearl necklace, natural pearls were reduced to a small, exclusive niche in the pearl industry.
Origin of a natural pearl
Previously, natural pearls were found in many parts of the world. Present-day natural pearling is confined mostly to seas off Bahrain. Australia also has one of the world's last remaining fleets of pearl diving ships. Australian pearl divers dive for south sea pearl oysters to be used in the cultured south sea pearl industry. The catch of pearl oysters is similar to the number of oysters taken during the natural pearl days. Hence significant numbers of natural pearls are still found in the Australian Indian Ocean waters from wild oysters. X-ray examination is required to positively verify natural pearls found today.
What are Organic Gems?
Although most gemstones are mineral materials, a number of organic materials are also considered to be gemstones. The most common of these are pearl, bone, amber, coral, jet, and ivory. These are materials, produced by organisms, that have been cut into gems and other ornamental objects.
There are also organic materials that have been mineralized (replaced and infilled by chalcedony, opal, calcite, aragonite, pyrite, or other mineral material). Although the material itself is not organic, it does preserve an organic structure. Examples include petrified wood, fossil coral, dinosaur bone, and other fossilized organisms or parts of organisms.
Table of Contents
Amber
Ammolite
Ammonite
Coral
Crinoids
Dinosaur Bone
Fossilized Coral and Bryozoans
Ivory
Jet
Mary Ellen Jasper
Mother of Pearl
Opalized Wood
Peanut Wood
Pearls
Petrified Palm
Petrified Wood
Sand Dollar
Turritella Agate