Obsidian is a occurring volcanic glass formed as an extrusive igneous rock. Obsidian is produced when felsic lava extruded from a volcano cools with minimal crystal growth, it is found within the margins of rhyolitic lava flows known as obsidian flows, where the chemical composition causes a high viscosity, upon rapid cooling, results in a natural glass forming from the lava. The inhibition of atomic diffusion through this viscous lava explains the lack of crystal growth. Obsidian is hard and amorphous. In the past, it was used to manufacture cutting and piercing tools, it has been used experimentally as surgical scalpel blades.... among the various forms of glass we may reckon Obsidian glass, a substance similar to the stone found by Obsidius in Ethiopia. The translation into English of Natural History by Pliny the Elder of Rome includes a few sentences about a volcanic glass called obsidian, discovered in Ethiopia by Obsidius, a Roman explorer. Obsidian is formed from cooled lava, the parent material.

Extrusive formation of obsidian may occur when felsic lava cools at the edges of a felsic lava flow or volcanic dome, or when lava cools during sudden contact with water or air. Intrusive formation of obsidian may occur. Tektites were once thought by many to be obsidian produced by lunar volcanic eruptions, though few scientists now adhere to this hypothesis. Obsidian is mineral-like, but not a true mineral, it is sometimes classified as a mineraloid. Though obsidian is dark in color, similar to mafic rocks such as basalt, obsidian's composition is felsic. Obsidian consists of SiO2 70% or more. Crystalline rocks with a similar composition include rhyolite; because obsidian is metastable at the Earth's surface, no obsidian has been found, older than the Cretaceous period. This transformation of obsidian is accelerated by the presence of water. Although newly-formed obsidian has a low water content less than 1% water by weight, it becomes progressively hydrated when exposed to groundwater, forming perlite.

Pure obsidian is dark in appearance, though the color varies depending on the impurities present. Iron and other transition elements may give the obsidian a dark brown to black color. Most black obsidians contain nanoinclusions of an iron oxide. Few samples of obsidian are nearly colorless. In some stones, the inclusion of small, radially clustered crystals of the mineral cristobalite in the black glass produce a blotchy or snowflake pattern. Obsidian may contain patterns of gas bubbles remaining from the lava flow, aligned along layers created as the molten rock was flowing before being cooled; these bubbles can produce interesting effects such as a golden sheen. An iridescent, rainbow-like sheen is caused by inclusions of magnetite nanoparticles creating thin-film interference. Colorful, striped obsidian from Mexico contains oriented nanorods of hedenbergite, which cause the rainbow striping effects by thin-film interference. Obsidian is found in locations, it can be found in Argentina, Azerbaijan, Canada, Georgia, El Salvador, Guatemala, Italy, Kenya, New Zealand, Papua New Guinea, Scotland and the United States.

Obsidian flows which may be hiked on are found within the calderas of Newberry Volcano and Medicine Lake Volcano in the Cascade Range of western North America, at Inyo Craters east of the Sierra Nevada in California. Yellowstone National Park has a mountainside containing obsidian located between Mammoth Hot Springs and the Norris Geyser Basin, deposits can be found in many other western U. S. states including Arizona, New Mexico, Texas and Washington, Oregon and Idaho. Obsidian can be found in the eastern U. S. states of Virginia and North Carolina. There are only four major deposit areas in the central Mediterranean: Lipari, Pantelleria and Monte Arci. Ancient sources in the Aegean were Gyali. Acıgöl town and the Göllü Dağ volcano were the most important sources in central Anatolia, one of the more important source areas in the prehistoric Near East; the first known archaeological evidence of usage was in Kariandusi and other sites of the Acheulian age dated 700,000 BC, although only few objects have been found at these sites relative to the Neolithic.

Use of obsidian in pottery of the Neolithic in the area around Lipari was found to be less at a distance representing two weeks journeying. Anatolian sources of obsidian are known to have been the material used in the Levant and modern-day Iraqi Kurdistan from a time beginning sometime about 12,500 BC; the first attested civilized use is dated to the late fifth millennium BC, known from excavations at Tell Brak. Obsidian was valued in Stone Age cultures because, like flint, it could be fractured to produce sharp blades or arrowheads. Like all glass and some other occurring rocks, obsidian breaks with a characteristic conchoidal fracture, it was polished to create early mirrors. Modern archaeologists have developed a relative dating system, obsidian hydration dating, to calculate the age of obsidian artifacts. Obsidian artifacts first appeared in the European continent in Central Europe in the Middle Pa

Margrave Otto V of Brandenburg-Salzwedel, nicknamed Otto the Tall, was a son of Margrave Otto III and co-ruler of Brandenburg with his cousin, Margrave Otto IV. Otto V spent many years at the court of his maternal uncle King Ottokar II of Bohemia; when Ottokar died in battle in 1278, Otto V became the regent for Ottokar's son and heir Wenceslaus II, only seven years old when his father died. As regent, Otto V had to deal with the machinations of Ottokar's widow Kunigunda of Slavonia and with factions of powerful noblemen. Bohemian chroniclers describe Otto's persistent rigour and that Wenceslaus was forced to give up his claims on Upper Lusatia before he could start reigning himself; when Wenceslaus had taken over, he and Otto V were still on good terms, Wenceslaus took measures against the strong influence of the group around his mother. Otto V persistently defended his claims on Pomerania against Polish counter-claims, he married with Judith of a daughter of Count Herman I of Henneberg. They had the following children: Matilda, the second wife of Henry IV Probus, Duke of Wrocław and High Duke of Poland Herman, his successor Otto Kunigunde, never married Beatrix, married Bolko I the Strict, Duke of Świdnica in 1284 Judith, married Rudolph I, Duke of Saxe-Wittenberg in 1303 Albert Otto von Heinemann, "Otto V.", Allgemeine Deutsche Biographie, 24, Leipzig: Duncker & Humblot, p. 663 Otto the Tall as Regent of Bohemia Entry at www.genealogie-mittelalter.de

Sorin Mircea Oprescu is a Romanian independent politician and medical doctor, Mayor of Bucharest between 2008 and 2015. Oprescu first ran for Mayor of Bucharest in 1998 backed by the Party of Social Democracy in Romania, the precursor to the modern-day Social Democratic Party, he was eliminated in the first round with 19.3 % of the vote. He ran again in 2000, achieving the highest first-round total but losing in the second round with 49.31% to winner Traian Basescu's 50.69%. He was one of the independent candidates running for president of Romania in the presidential elections which took place on 22 November 2009, he was eliminated in the first round with 3.18% of the vote, was involved in a notable Condorcet cycle with Mircea Geoana and eventual winner Traian Basescu. He was a senator representing the Social Democratic Party between 2000 and April 2008, serving as the vice-president of the Senate Committee for Public Health. Oprescu resigned from the Senate on 24 June 2008. In February 2006, Oprescu became the president of the Social Democratic Party's Bucharest branch, a position from which he stepped down upon quitting the party in April 2008.

In 2008, after the Social Democratic Party refused to nominate him to the mayoral elections, he ran as an independent candidate. He earned the most votes in the first round of the elections. In the second round against the Democratic-Liberal Party candidate Vasile Blaga, with the support of the Liberals and Social-Democrats, he won with 56.55% of the vote. The Social-Democrat mayor of Bucharest's Sector 2, Neculai Onţanu, announced he supported Blaga, while the Social-Democrat mayor of Sector 5, Marian Vanghelie, announced he would not support Oprescu and accused him of being a "cheap demagogue". In September 2015, he was arrested on charges of corruption. On 15 September 2015, being deposed by Bucharest's Prefect upon a courts' decision to maintain Oprescu's arrest, an interim successor was elected from one of the city's deputy-mayors. Sorin Oprescu - official site