Hymn of the Pearl

Pearl

A pearl is a hard, rounded object produced within the soft tissue (specifically the mantle) of a living shelled mollusk. Just like the shell of mollusks, a pearl is composed of calcium carbonate in minute crystalline form, which has been deposited in concentric layers. The ideal pearl is perfectly round and smooth, but many other shapes of pearls occur, see baroque pearl.
The finest quality pearls have been highly valued as gemstones and objects of beauty for many centuries, and the word pearl has become a metaphor for something rare, fine, and admirable.
Almost any shelled mollusk can, by natural processes, produce some kind of "pearl" when an irritating microscopic object becomes trapped within the mollusk's mantle folds, but virtually none of these "pearls" are considered to be gemstones.

Physical properties

The unique luster of pearls depends upon the reflection and refraction 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.
Pearls are often white or cream, but the color can vary quite a lot according to the natural color of the nacre in the various species of mollusk used. Thus pearls can also be black, or various pastel shades. In addition, pearls (especially freshwater pearls) can be dyed yellow, green, blue, brown, pink, purple, or black.

Freshwater and saltwater pearls

Freshwater pearls form in various species of freshwater mussels, family Unionidae, which live in lakes, rivers, ponds and other bodies of fresh water. These freshwater pearl mussels occur not only in hotter climates, but also in colder more temperate areas such as Scotland, see the freshwater pearl mussel. However, most freshwater cultured pearls sold today come from China.

Creation of a pearl

The difference between natural and cultured pearls focuses on whether the pearl was created spontaneously by nature — without human intervention, or with human aid. Pearls are formed inside the shell of certain bivalve mollusks: as a response to an irritant inside its shell, the mollusk creates a pearl to seal off the irritation.
The mantle of the mollusk deposits layers of calcium carbonate (CaCO3) in the form of the minerals aragonite or calcite (both crystalline forms of calcium carbonate) held together by an organic horn-like compound called conchiolin. This combination of calcium carbonate and conchiolin is called nacre, or as most know it, mother-of-pearl.

Natural pearls

Natural pearls are nearly 100% nacre. It is thought that natural pearls form under a set of accidental conditions when a microscopic intruder or parasite enters a bivalve mollusk, and settles inside the shell. The mollusk, being irritated by the intruder, secretes the calcium carbonate substance called nacre to cover the irritant. This secretion process is repeated many times, thus producing a pearl.

Cultured pearls

Cultured pearls (nucleated and non-nucleated or tissue nucleated cultured pearls) and imitation pearls can be distinguished from natural pearls by X-ray examination. Nucleated cultured pearls are often 'pre-formed' as they tend to follow the shape of the implanted shell bead nucleus. Once the pre-formed beads are inserted into the oyster, it secretes a few layers of nacre around the outside surface of the implant before it is removed after six months or more.

Gemological identification

Natural and cultured pearls can be distinguished from imitation pearls using a microscope. Another method of testing for imitations is to rub the pearl against the surface of a front tooth. Imitation pearls are completely smooth, but natural and cultured pearls are composed of nacre platelets, which feel slightly gritty.

Value of a natural pearl

Quality natural pearls are very rare jewels. The actual value of a natural pearl is determined in the same way as it would be for other "precious" gems. The valuation factors include size, shape, quality of surface, orientation, and luster.
Single natural pearls are often sold as a collector's item, 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. Yachtsman and financier Cartier purchased the landmark Cartier store on Fifth Avenue in New York for $100 cash and a double strand of matched natural pearls valued at $1 million.

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 numbers 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.

Different types of cultured pearls
Black pearls, frequently referred to as Black Tahitian Pearls, are highly valued because of their rarity.This is simply due to the fact that the black pearl oyster Pinctada margaritifera is far more abundant than the elusive, rare, and larger south sea pearl oyster - Pinctada maxima, which cannot be found in lagoons, but which must be dived for in a rare number of deep ocean habitats. Black cultured pearls from the black pearl oyster — Pinctada margaritifera — are NOT south sea pearls, although they are often mistakenly described as black south sea pearls. In the absence of an official definition for the pearl from the black oyster, these pearls are usually referred to as "black Tahitian pearls". The correct definition of a south sea pearl — as described by CIBJO and the GIA — is a pearl produced by the Pinctada maxima pearl oyster. South sea pearls are the color of their host Pinctada maxima oyster — and can be white, silver, pink, gold, cream, and any combination of these basic colors, including overtones of the various colors of the rainbow displayed in the pearl nacre of the oyster shell itself.

Other "pearls"

Biologically speaking, under the right set of circumstances, almost any shelled mollusk can produce some kind of "pearl," however, most of these molluscan "pearls" have no luster or iridescence. One unusual example of calcareous concretions which nonetheless can sometimes have value, are the "pearls" which are found very rarely growing between the mantle and the shell of the queen conch or pink conch, Strombus gigas, a large sea snail or marine gastropod from the Caribbean Sea. These "pearls", which are pink in color, are a by-product of the conch fishing industry, and the best of them show some chatoyance.

The largest example of another "pearl"

The largest "pearl" known, was found in the Philippines in 1934. It is a naturally-occurring, non-nacreous, calcareous concretion from a giant clam. Because it did not grow in a pearl oyster it is not pearly, instead it has a porcellaneous surface, in other words it is glossy like a china plate. Gemologically speaking, it is not a pearl.

Pearls in jewelry

The value of the pearls in jewelry is determined by a combination of the luster, color, size, lack of surface flaw and symmetry that are appropriate for the type of pearl under consideration. Among those attributes, luster is the most important differentiator of pearl quality according to jewelers. All factors being equal, however, the larger the pearl the more valuable it is. Large, perfectly round pearls are rare and highly valued. Teardrop-shaped pearls are often used in pendants.

An opera will be long enough to reach the breastbone or sternum of the wearer, and longer still, a pearl rope is any length that falls down farther than an opera.

Necklaces can also be classified as uniform, or graduated. In a uniform strand of pearls, all pearls are classified as the same size, but actually fall in a range. A uniform strand of akoya pearls, for example, will measure within 0.5 mm. So a strand will never be 7 mm, but will be 6.5-7 mm. Freshwater pearls, Tahitian pearls, and South Sea pearls all measure to a full millimeter when considered uniform. A graduated strand of pearls most often has at least 3 mm of differentiation from the ends to the center of the necklace. Popularized in the 1950s by the GIs bringing strands of cultured akoya pearls home from Japan, the graduated style was much more affordable as most pearls in any given strand were small.

Religious references

According to Rebbenu Bachya, the word Yahalom in the verse Exodus 28:18 means "pearl" and was the stone on the Hoshen representing the tribe of Zebulun. This is extremely disputed among scholars, particularly since the word in question in most manuscripts is actually Yasepheh - the word from which jasper derives.

In different translations of the Bible — the King James Version translates the sixth stone as diamond, the New International Version translates it as emerald, and the Vulgate translates it as jaspis — meaning jasper.

In a Christian New Testament parable, Jesus compared the Kingdom of Heaven to a "pearl of great price" in Matthew 13: 45-46. "Again, the kingdom of heaven is like unto a merchant man, seeking goodly pearls: Who, when he had found one pearl of great price, went and sold all that he had, and bought it."

Islamic references

In Islam, the Koran often mentions that dwellers of paradise will be adorned with pearls:
22:23 God will admit those who believe and work righteous deeds, to Gardens beneath which rivers flow: they shall be adorned therein with bracelets of gold and pearls; and their garments there will be of silk.
35:33 Gardens of Eternity will they enter: therein will they be adorned with bracelets of gold and pearls; and their garments there will be of silk.
The Quran describes the wives of the people of Paradise as having eyes that are similar to pearls:
56:22-23 And [there will be] Houris with wide lovely eyes [as wives for the pious], Like unto preserved pearls.
The handsome young boys in paradise are similarly depicted:
52:24 Round about them will serve, [devoted] to them, youths [handsome] as Pearls well-guarded.

Hindu astrological belief in natural pearls

The Vedic tradition describes the sacred Nine Pearls which were first documented in the Garuda Purana, one of the books of the Hindu holy text Atharvaveda. Ayurveda contains references to pearl powder as a stimulant of digestion and to treat mental ailments. According to Marco Polo the kings of Malabar (now known as the Coromandel Coast) wore a necklace of 104 rubies and 104 precious pearls which was given from one generation of kings to the next. The reason was that every king had to say 104 prayers to his "idols" every morning and every evening. At least until the beginning of the 20th century it was a Hindu custom to present a completely new, undrilled pearl and pierce it during the ceremony.