Pearls are one of the few organic gems which are buildup of mother of pearl (nacre) mainly calcium carbonate, organic compounds and water 

Although the moh’s hardness is only 2 1/2 − 4 1/2,pearls are extraordinarily compact, and it is very difficult to crush them The derivation of the name pearl is uncertain, but may be from a type of shell (latin-perna) or from its spherical shape (latin-sphaerula).Pearls have been found in variety of sizes, one of the largest fine pearls ever found ( called the Hope pear after a former owner ) is 5 cm long and weighs 454 ct . it is in the south Kensington museum in London 

Formation

Pearls are formed by saltwater oysters (genus Pinctada) , some fresh-water mussels ( unio ),and more rarely by other shellfishPearls are formed as a result of an irritant that has intruded between the shell of the mollusk and mantle or into the interior of the mantle 

If a pearl is formed as a wart-like growth on the inside of the shell it must be separated from the shell by secretion of mother of pearl. When it is collected, it is called bliste or shell pearl

The typical pearly luster is produced by over lapping platelets of aragonite and film of conchiolin nearer to the pearl surface. (results in iridescent colors called orient) The color of the pears varies with the type of mollusk and water and it is dependent on upper conchiolin layer. Pearls can have wide variety of colors such as: white, pink, silver-, cream-, golden-colored, green, blue, black. When a foreign body enters the inner part of the mantle, the mollusk forms a nonattached, rounded pearls as a type of immunity defense. The nacre can also produce a pearl without any foreign body

Natural pearls

Natural pearls are those that come into being without intervention by human beings

Sea pearls

The most important occurrences yielding the best qualities (rose and creamy white) have long been those in the vicinity of the Persian gulf, because of this occurrence, all natural sea water pearls, wherever they come from, have been called “oriental pearls” in the trade. Also, in the gulf of Mannar, there are ancient beds (pearls of pink-red and soft yellow color), but the pearls are mostly small (so-called seed-pearls). Other important occurrences are along cost of Madagascar, Burma (Myanmar), the Philippines, many island in the south pacific,northern Japan , the most important country of cultured pearl production ,there are only some small beds with natural pearls. Pearls are harvested by divers. The giant conch (stormbus gigas) is a sea snail that produces pearls. Most gemologists do not consider it a true pearl because it lacks nacre

River pearls

Fishing for natural pearls in freshwater, the river pearls, is today of no great importance commercially; they are rarely of good quality. because of the pollution of the water, pearl mussel have not flourished or become extinct. In the Scandinavian countries and in central Europe, pearl mussels are environmentally protected; pearl fishing is forbidden. A limited number of natural freshwater pearls is still obtained from rivers in the united states

Cultured pearls

century due to depletion and pollution, After reduction of natural pearls supplies in the 20th the increase demand for pearls has led to their cultivation in large scale, there are culturedpearls form in the ocean as well as in freshwater

Saltwater cultured pearls

The principle behind pearl culturing is simple. humans cause the mollusk to produce a pearl century, small objects were fixed to th by insertion of foreign body. In china as early as the 13 inner wall of a mollusk shell so that they would be covered with pearl material. Round pearls were first produced.to stimulate the mollusks to produce pearls, rounded mother-of-pearl beads from the shell of the north American freshwater mussel are at first wrapped with a piece of tissue from the mantle of a pearl mollusk (pincatada martensii),and are then inserted into the cell lining of the mantle of another pearl mollusk. The most important element in the production of a pearl is the tissue, not the foreign body. It has been proven that one can do without the bead, but then the process will not remain economical since the culture of a large pearl takes too much time

Cultured freshwater pearls

Cultivation methods are the same as for the sea mollusks. Cages are hung on a bamboo frame. The success rate is about 60 percent with is clearly higher than in sea water. The life of a freshwater mussel is 13 years, but after the operation it produces mother-of-pearl only for three more years. Many mussels can be harvested three times. Freshwater pearls are cultivated in Biwalaka (japan), china

Use and Validation of pearls

Pearls have been regarded as one of the most valuable gem materials. They have been used for adornment for 6,000 years. Pearls are also popular because they do not require any processing; in their natural state they show their full gloss,the desired luster

Uses

A point of the pearl, which either has a mark or is less perfect, is chosen for drilling a hole, thus eliminating the mark. Blue pearls should never be drilled, as they may change color when air reaches the drill hole. Spotted or damaged pearls can be peeled, i.e., the outer layer can be removed. Badly damage parts can be cut away; the remaining part is traded as half or three quarter pearl (not to be confused with blister pearls). They are used mainly for earrings and brooches

Valuation

The pearl is valued according to shape, color, size, surface condition, and luster. the most valuable is the spherical shape. Those flattened on one side or half-spherical pearls are called boutton (French-button) or button pearls; irregular pearls are baroque pearls. Pearls long worn in a necklace take on the shape of a little barrel; one speaks of barrel pearls. Natural pears are weighed in grains (1 grain 0.05g=0.024ct or 1/4 carat), and today increasingly in carat. Traditionally natural pearl prices were calculated according to weight. Except in large wholesale transactions, cultured pearl prices are normally quoted with regard to size. The word pearl without addition should be used only for natural pearls. Cultured pearls be designated as such

Taking care of pearls

Since conchiolin is an organic substance, it is prone to change, especially to drying out. This can lead to an “aging” of the pearls, limiting their useful life. there are no guarantee possible for the life span of a pearl; on average , one estimated 100 to 150 years. But there are pearls which are some hundred of years old and still look their best. Acids, perspiration, cosmetics, and hair spray can damage a pearl. Since pearls have a low hardness, they can be easily scratched. Therefore, wear and store them in such a way that the pearl surface is never in contact with metal or other gemstones

Discerning pearls from imitations

As is the case for all gemstones, there are numerous imitations of pearls on the market. To recognize these is just as important as the differentiation between natural and cultured pearls, because there is huge disparity in respective prices

Differentiating between natural and cultured pearls

There is little or no difference in the appearance of natural and cultured pearls. To differentiate between them is difficult. Their density can help, as it is greater than 2,73 in the case of most (but not all) cultured pearls, whereas the density of natural pearls is usually lower. sometimes an examination with certain radiation can clarify. Under ultra violet light, for instance, cultured pearls have a yellow luminescence, and under X rays a green one, but these reactions are not completely dependable. One reliable method of differentiating between cultured and natural pearls is by examining their inner structure. Natural pearls have a concentrically layered structure, whereas the inner structure of the cultured pearl varies according to the type of bead. Typically, an expert uses an instrument like an endoscope to explore the structure of the pearl inside the drilling hole. Radiography methods with X rays, such as the X ray diffraction method and the X ray silhouette procedure, are effective

 Imitations

A fine imitation is the so-called fish-scale pearl. It consist of glass or enamel coated with essence d’orient, which is produced from the scales of certain fish. In other imitations, part of sea snail, mussels, or teeth are used. The mabe pearl may also be included among the imitations, because this is not a cultured pearl in the trade sense. It consist of thin mother-ofpearl layer and some other artificial parts. A clay or resin bead is fixed to inner part of a shell and then is covered with a thin pearl layer. After the harvest the bead is removed and replaced by a mother-of-pearl half-bead. The nacre shell is then filled with epoxy and centered to a mother-of-pearl backing

Operculum

Operculum (misleadingly called chines cat’s eye) has a structure similar to a half-pearl, with a porcelain-type coloring, but is actually the slightly arched lid of a sea snail found in the Australasian islands area, where it is used for adornment. It is not well known in Europe or the united states

Mother-of-pearl

The inner nacreous layer of a mollusk shell, or sometimes of a snail shell which has an iridescent play of color, is called mother-of-pearl (“mother of the pearl”)

Mother-of-pearl: The main suppliers are the pearl farms. The basic color is usually white;it is naturally dark in the mother-of-pearl from Tahiti. Mother of the pearl is favorably used for ornamental purposes, for clock faces, buttons, costume jewelry, and for inlaid work (such as handle of knives and pistols)

Mother-of-pearl of the Paua (abalone)

The mother-of-pearl of the Paua from New Zealand, which has a blue green iridescent color play. The mother-of-pearl of this mollusk has now been used for some time in the Western world, especially for costume jewelry. It is called sea opal, because of a resemblance to the color effect seen in opal