Buenos Aires is the capital and largest city of Argentina. It is geographically located on the southern shore of the Río de la Plata, on the southeastern coast of the South American continent. Greater Buenos Aires is the third largest conurbation in Latin America, with a population of about 13 million. In English, Buenos Aires means "Fair Winds" or "Good Air." After the internal conflicts of the 19th century, Buenos Aires was federalised and removed from Buenos Aires Province in 1880. The city limits were enlarged to include the former towns of Belgrano and Flores, which are both now neighbourhoods of the city. During most of the 19th century, the political status of the city remained a sensitive subject. It was already capital of Buenos Aires Province, and between 1853 and 1860 it was the capital of the seceded State of Buenos Aires. The issue was debated more than once on the battlefield, until the matter was finally settled in 1880 when the city was federalised and became the seat of government, with its Mayor appointed by the President. The Casa Rosada became the seat of the office of the President. In addition to the wealth generated by the fertile pampas, railroad construction in the second half of the 19th century increased the economic power of Buenos Aires as raw materials flowed into its factories; Buenos Aires became a multicultural city that ranked itself with the major European capitals. The Colón Theater became one of the world's top opera venues. The city's main avenues were opened mostly between 1880 and 1940, an era that also saw the construction of South America's then-tallest buildings and first underground system.

Pearls

The finest quality natural pearls have been highly valued as gemstones and objects of beauty for many centuries, and because of this, the word pearl became a metaphor for something very rare, very fine, very admirable and very valuable. A pearl is a hard, round object produced within the soft tissue of a living shelled mollusk. Just like the shell of mollusks, a pearl is composed of calcium carbonate in minute crystalline form, which been deposited in concentric layers. The ideal pearl is perfectly round and smooth, but many other shapes of pearls occur. 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 valued as gemstones. A black pearl and a shell of the black-lipped pearl oyster are interesting. Two groups of mollusk can bivalves or clams produce saltwater pearl oyster farm, Serum, Indonesia Nacreous pearls, and the most desirable pearls. One family lives in the sea: the pearl oysters. The other, very different group of bivalves live in freshwater, and these are the river mussels. Saltwater pearls can grow in several species of marine pearl oysters in the family Pteriidae. Freshwater pearls grow within certain) species of freshwater mussels in the order Uniondale, the families Uniondale and Margaritiferidae. These various species of bivalves are able to make nacreous pearls because they have a thick iridescent inner shell layer called mother of pearl, which is composed of nacre. The mantle tissue of a living bivalve can create a pearl in the same manner that it creates the pearly inner layer of the shell.