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A pearl is a hard, glistening object produced within the soft tissue (specifically the mantle) of a living shelled mollusk or another animal, such as fossil conulariids. Just like the shell of a mollusk, a pearl is composed of calcium carbonate (mainly aragonite or a mixture of aragonite and calcite) in minute crystalline form, which has deposited in concentric layers. The ideal pearl is perfectly round and smooth, but many other shapes, known as baroque pearls, can occur. The finest quality of natural pearls have been highly valued as gemstones and objects of beauty for many centuries. Because of this, pearl has become a metaphor for something rare, fine, admirable and valuable.
The most valuable pearls occur spontaneously in the wild, but are extremely rare. These wild pearls are referred to as natural pearls. Cultured or farmed pearls from pearl oysters and freshwater mussels make up the majority of those currently sold.
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Gelsenkirchen (UK: , US: , German: [ˌɡɛlzn̩ˈkɪʁçn̩] (listen); Westphalian: Gelsenkiärken) is the 11th largest city of Germany's most populous federal state of North Rhine-Westphalia and its 262,528 (2016) inhabitants make it the 25th largest city of Germany. On the Emscher River (a tributary of the Rhine), it lies at the centre of the Ruhr, the largest urban area of Germany, of which it is the fifth largest city after Dortmund, Essen, Duisburg and Bochum. The Ruhr is located in the Rhine-Ruhr Metropolitan Region, one of Europe's largest urban areas. Gelsenkirchen is the fifth largest city of Westphalia after Dortmund, Bochum, Bielefeld and Münster, and it is one of the southernmost cities in the Low German dialect area. The city is home to the football club Schalke 04, which is named after Gelsenkirchen-Schalke. The club's current stadium Veltins-Arena, however, is located in Gelsenkirchen-Erle.
Gelsenkirchen was first documented in 1150, but it remained a tiny village until the 19th century, when the Industrial Revolution led to the growth of the entire area.