Pearl freshwater

Araujo R, Ramos MA (2000) Status and conservation of the giant European freshwater pearl mussel Margaritifera auricularia (Spengler, 1793) (Bivalvia Unionoidea). Biol Conserv 96 233-239... 

Lopez MA, Altaba CR, Rouault T, Gisbert E (2007) The European sturgeon Acipenser sturio is a suitable host for the glochidia of the freshwater pearl mussel Margaritifera auricularia. J Molluscan Stud 73 207-209... 

Cultured freshwater pearls are produced by placing a tiny piece of mande tissue inside the shell. Some bivalves can take many of these tissue seeds at the same time, unlike marine oysters, which will usually only make one or two pearls at a time. 

Fracture Fracture describes the way a substance breaks when it neither cleaves nor parts (breaks along plane of weakness). The most common kind of visible fracture is conchoidal, which produces curved, smooth surfaces (glass, quartz). Freshwater pearl one that occurs in a freshwater (non-marine) mollusk. Gem a general term used to describe precious and semi-precious stones, usually after they have been cut and polished. In archaeology, it refers only to engraved stones (cameo, intaglio, seals, etc.). 

It is also possible to divide the groups into marine and freshwater pearls. The molluscs that produce these two types of pearls are termed marine pearl oysters and freshwater mussels. 

Pearls can be soaked in hydrogen peroadde to bleach them. This used to be routine with Chinese freshwater pearls as their colour was not good, but is probably less necessary today as the quality of the peails from China is much improved. Bleaching tended to dry out the organic matrix in the pearls and cause them to become britde (Fig. 9.13). 

Ultraviolet light. PearlH from zmirine oysters fluoresce a chalky-white under UV light, while some freshwater pearls fruoresce a yellowish colour. However, coated plastic pearls can also fluoresce 8 yellow colour. As diell - and therefore diell beads - have the same fluorescence as marine pearls, the test is not conclusive. 

There are records of diving for pearls in 200 BC in the Arabian Gulf, and the Chinese have used freshwater pearls since antiquity. For centuries they traded for them, even obtaining them from Japan where pearls were not yet popular. 

Schone, B.R., Dunca, H., Mutvei, H. Norlund, U. (2004) A 217-year record of summer air temperature reconstructed from freshwater pearl mussels (M. margarifitera, Sweden). Quaternary Science Reviews 23, 1803-1816. 

BAi, z., YIN, Y., HU, s., WANG, G., ZHANG, X. LI, j. 2009. Identification of genes involved in immune response, microsatellite, and SNP markers from expressed sequence tags generated from hemocytes of freshwater pearl mussel (Hyriopsis cumingii). Mar Biotechnol (NY), 11(4) 520-530. 

Zhou, H.Y., Wong, M.H., 2004. Screening of organochlorines in freshwater fish collected from the Pearl River Delta, People s Republic of China. Arch. Environ. Contam. Toxicol. 46, 106-113. 

The Biwa pearl mussel, Hyriopsis schlegelii, is probably the most famous of the freshwater mussels. It was native to Lake Biwa in Japan, though the stocks are now very depleted. It was used in the production of Biwa pearls, which were the first freshwater, non-nucleated cultured pearls to come on the market. They were of an irregular oval shape. 

The cockscomb pearl mussel, Cristaria plicata, lives in Japan and China. It produced the original rice-krispie pearls. They were small, irregular in shape, and had a wrinkled appearance. They were naturally white, but were frequently dyed. The mussels have thin shells and, when pearl cultivation was first attempted in China, were proved to be incapable of producing freshwater cultured pearls of high enough quality. 

The triangleshell pearl mussel, Hyriopsis cumingii, is the oyster now used in China to produce their freshwater cultured pearls, which are of a vastly superior quality to their original rice-krispies . The triangleshell is also farmed in Japan. It has a much thicker shell than the cockscomb, and it can produce nearly perfect round pearls with a good lustre. The naturally coloured nacre occurs in whites, orange-browns and blue-greys. White is the most popular colour (Fig. 9.5). 

The European pearl oyster, Margaritifera margaritifera, is of historic interest as it was the source of most of the European freshwater natural pearls. It was native to Europe and parts of North... 

There are many natural and cultured pearls of interesting shapes that come onto the market. The freshwater mussels of the eastern United States produce natural pearls that are usually silvery ute> often have a slighdy silky sheen rather than a pearly lustre and can be an amazing variety of shapes (Fig. 9.7). 

Many years after the original pearl cultivation was started, it was realised that it was not necessary to insert a hard nucleus into an oyster to induce it to produce a pearl, and that it was sufficient simply to insert a piece of mantle. This is the method favoured by the Chinese, and gives non-nucleated cultured pearls . The pearls are grown in freshwater mussels, suspended from floats in lakes and rivers. Up to 30 mantle grafts are inserted into a single host mussel s mantle tissue, just inside the shell. 

Marine pearl oysters that are umed ate all nudeated with a bead and a piece of mantle tissue. Freshwater mussels that ate farmed are implanted with mantle tissue grafts only. In some areas the oysters and mussels to be used are bred and cultivated until they reach maturity and can be implanted. In other areas oysters are cau t in the wild to be cultivated. 

A nucleus of a different colour to the nacre is an obvious sign of a nucleated cultured pearl. A dark bead beneath white nacre will give the impression of a grey pearl. It is probable that the pearl has been irradiated as this process darkens the freshwater mother-of-pearl bead rather than the nacre produced by a marine oyster. It is also possible that the bead has been dyed. 

The famous Biwa cultured pearls, named after the lake where they were farmed in Japan, were almost completely exterminated in the 1970s and 1980s. This was caused by a combination of factors, which included pollution from agricultural waste, overfishing, and a freshwater form of red tide. It is taking years to restock the lake with the mussels needed to produce these pearls. 

Some shells have a porcellaneous inner layer, while others produce a nacreous layer. The nacreous effect is called mother-of-pearl and is caused by tiny, overlapping platelets of calcium carbonate in the form of aragonite, which disperse the light to give a play-of-colour. The platelets are polygonal and lie horizontal to the surface. In gastropods and nautilus they are stacked like coins, but they can also be alternated, like a brick wall, as is the case in most bivalves. There can be more than one nacreous layer, as in, for example, freshwater mussels. 

Some of the freshwater mussels that produce pearls also display attractive shells. The cultured pearl industry is very dependent upon beads made from freshwater mussel shells (Fig. 9.10), notably the washboard and pigtoe mussels, which are used for nuclei for cultured pearls. 

Pure white mother-of-pearl buttons, made from freshwater mussels, may have to be viewed under a microscope to see the aragonite platelets. Lack of these indicates a plastic imitation. 

As with SO many animals the conservation status of the various species changes from year to year. Nautilus has been thought to be endangered but is still widely sold, while some of the freshwater mussels, from which mother-of-pearl nuclei are made for the cultured pearl industry, are in real danger of extinction and are now protected. 

At one time the mother-of-pearl button industry was huge indeed it was so big that it almost wiped out entire populations of freshwater mussels in North America. The industry was in turn almost kUled off by the advent of plastics. Today some buttons are still produced in the Far East and are made mostly from trochus shell. A few more exotic - and expensive - examples from other shells are also manufactured. 

Cultured Pearl farming Asia-Pacific region Marine and freshwater Suspended rope 0.0012 0.46 Low... 

Figs. 5.8b and c show the variation in DIN concentrations in a vertical direction in the ebb and flood tides respectively. The results indicated that both in the northern area and southern area of the estuary, the variation was not apparent in a vertical direction, while the concentration in the surface layer was higher than that in the bottom layer in the middle area. The reason is that the middle area is influenced by the invasion of the briny wedge, the freshwaters from nmoff mainly concentrate on the surface, and the seawater is distributed at the bottom, while the water system in the southern and northern areas is well mixed in a vertical direction. This also indicated that the runoff of the Pearl River was the chief source of the DIN from another point of view. 

Mother-of-pearl is produced primarily from the shells of the freshwater species, which are boiled in alkaline water followed by soaking in fresh water. The dark surface layer is then scraped off and the shells are baked until crisp. Better grades are white, come in large pieces, and are crisp. Much of the commercial mother-of-pearl is produced from shells that are byproducts of buttons production. Major producers are the same as those of pearl (nahonal zcyx). 

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