Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. At room temperature and pressure, another solid form of carbon known as graphite is the chemically stable form, but diamond never converts to it. Diamond has the highest hardness and thermal conductivity of any natural material, properties that are utilized in major industrial applications such as cutting and polishing tools, they are the reason that diamond anvil cells can subject materials to pressures found deep in the Earth. Because the arrangement of atoms in diamond is rigid, few types of impurity can contaminate it. Small numbers of defects or impurities color diamond blue, brown, purple, orange or red. Diamond has high optical dispersion. Most natural diamonds have ages between 1 billion and 3.5 billion years. Most were formed at depths between 150 and 250 kilometers in the Earth's mantle, although a few have come from as deep as 800 kilometers. Under high pressure and temperature, carbon-containing fluids dissolved minerals and replaced them with diamonds.
Much more they were carried to the surface in volcanic eruptions and deposited in igneous rocks known as kimberlites and lamproites. Synthetic diamonds can be grown from high-purity carbon under high pressures and temperatures or from hydrocarbon gas by chemical vapor deposition. Imitation diamonds can be made out of materials such as cubic zirconia and silicon carbide. Natural and imitation diamonds are most distinguished using optical techniques or thermal conductivity measurements. Diamond is a solid form of pure carbon with its atoms arranged in a crystal. Solid carbon comes in different forms known as allotropes depending on the type of chemical bond; the two most common allotropes of pure carbon are graphite. In graphite the bonds are sp2 orbital hybrids and the atoms form in planes with each bound to three nearest neighbors 120 degrees apart. In diamond they are sp3 and the atoms form tetrahedra with each bound to four nearest neighbors. Tetrahedra are rigid, the bonds are strong, of all known substances diamond has the greatest number of atoms per unit volume, why it is both the hardest and the least compressible.
It has a high density, ranging from 3150 to 3530 kilograms per cubic metre in natural diamonds and 3520 kg/m³ in pure diamond. In graphite, the bonds between nearest neighbors are stronger but the bonds between planes are weak, so the planes can slip past each other. Thus, graphite is much softer than diamond. However, the stronger bonds make graphite less flammable. Diamonds have been adapted for many uses because of the material's exceptional physical characteristics. Most notable are its extreme hardness and thermal conductivity, as well as wide bandgap and high optical dispersion. Diamond's ignition point is 720 -- 800 °C in 850 -- 1000 °C in air; the equilibrium pressure and temperature conditions for a transition between graphite and diamond is well established theoretically and experimentally. The pressure changes linearly between 1.7 GPa at 0 K and 12 GPa at 5000 K. However, the phases have a wide region about this line where they can coexist. At normal temperature and pressure, 20 °C and 1 standard atmosphere, the stable phase of carbon is graphite, but diamond is metastable and its rate of conversion to graphite is negligible.
However, at temperatures above about 4500 K, diamond converts to graphite. Rapid conversion of graphite to diamond requires pressures well above the equilibrium line: at 2000 K, a pressure of 35 GPa is needed. Above the triple point, the melting point of diamond increases with increasing pressure. At high pressures and germanium have a BC8 body-centered cubic crystal structure, a similar structure is predicted for carbon at high pressures. At 0 K, the transition is predicted to occur at 1100 GPa; the most common crystal structure of diamond is called diamond cubic. It is formed of unit cells stacked together. Although there are 18 atoms in the figure, each corner atom is shared by eight unit cells and each atom in the center of a face is shared by two, so there are a total of eight atoms per unit cell; each side of the unit cell is 3.57 angstroms in length. A diamond cubic lattice can be thought of as two interpenetrating face-centered cubic lattices with one displaced by 1/4 of the diagonal along a cubic cell, or as one lattice with two atoms associated with each lattice point.
Looked at from a <1 1 1> crystallographic direction, it is formed of layers stacked in a repeating ABCABC... pattern. Diamonds can form an ABAB... structure, known as hexagonal diamond or lonsdaleite, but this is far less common and is formed under different conditions from cubic carbon. Diamonds occur most as euhedral or rounded octahedra and twinned octahedra known as macles; as diamond's crystal structure has a cubic arrangement of the atoms, they have many facets that belong to a cube, rhombicosidodecahedron, tetrakis hexahedron or disdyakis dodecahedron. The crystals can be elongated. Diamonds are found coated in nyf, an opaque gum-like skin; some diamonds have opaque fibers. They are referred to as opaque if the fibers
New York City
The City of New York called either New York City or New York, is the most populous city in the United States. With an estimated 2017 population of 8,622,698 distributed over a land area of about 302.6 square miles, New York is the most densely populated major city in the United States. Located at the southern tip of the state of New York, the city is the center of the New York metropolitan area, the largest metropolitan area in the world by urban landmass and one of the world's most populous megacities, with an estimated 20,320,876 people in its 2017 Metropolitan Statistical Area and 23,876,155 residents in its Combined Statistical Area. A global power city, New York City has been described as the cultural and media capital of the world, exerts a significant impact upon commerce, research, education, tourism, art and sports; the city's fast pace has inspired the term New York minute. Home to the headquarters of the United Nations, New York is an important center for international diplomacy.
Situated on one of the world's largest natural harbors, New York City consists of five boroughs, each of, a separate county of the State of New York. The five boroughs – Brooklyn, Manhattan, The Bronx, Staten Island – were consolidated into a single city in 1898; the city and its metropolitan area constitute the premier gateway for legal immigration to the United States. As many as 800 languages are spoken in New York, making it the most linguistically diverse city in the world. New York City is home to more than 3.2 million residents born outside the United States, the largest foreign-born population of any city in the world. In 2017, the New York metropolitan area produced a gross metropolitan product of US$1.73 trillion. If greater New York City were a sovereign state, it would have the 12th highest GDP in the world. New York is home to the highest number of billionaires of any city in the world. New York City traces its origins to a trading post founded by colonists from the Dutch Republic in 1624 on Lower Manhattan.
The city and its surroundings came under English control in 1664 and were renamed New York after King Charles II of England granted the lands to his brother, the Duke of York. New York served as the capital of the United States from 1785 until 1790, it has been the country's largest city since 1790. The Statue of Liberty greeted millions of immigrants as they came to the U. S. by ship in the late 19th and early 20th centuries and is an international symbol of the U. S. and its ideals of liberty and peace. In the 21st century, New York has emerged as a global node of creativity and entrepreneurship, social tolerance, environmental sustainability, as a symbol of freedom and cultural diversity. Many districts and landmarks in New York City are well known, with the city having three of the world's ten most visited tourist attractions in 2013 and receiving a record 62.8 million tourists in 2017. Several sources have ranked New York the most photographed city in the world. Times Square, iconic as the world's "heart" and its "Crossroads", is the brightly illuminated hub of the Broadway Theater District, one of the world's busiest pedestrian intersections, a major center of the world's entertainment industry.
The names of many of the city's landmarks and parks are known around the world. Manhattan's real estate market is among the most expensive in the world. New York is home to the largest ethnic Chinese population outside of Asia, with multiple signature Chinatowns developing across the city. Providing continuous 24/7 service, the New York City Subway is the largest single-operator rapid transit system worldwide, with 472 rail stations. Over 120 colleges and universities are located in New York City, including Columbia University, New York University, Rockefeller University, which have been ranked among the top universities in the world. Anchored by Wall Street in the Financial District of Lower Manhattan, New York has been called both the most economically powerful city and the leading financial center of the world, the city is home to the world's two largest stock exchanges by total market capitalization, the New York Stock Exchange and NASDAQ. In 1664, the city was named in honor of the Duke of York.
James's older brother, King Charles II, had appointed the Duke proprietor of the former territory of New Netherland, including the city of New Amsterdam, which England had seized from the Dutch. During the Wisconsinan glaciation, 75,000 to 11,000 years ago, the New York City region was situated at the edge of a large ice sheet over 1,000 feet in depth; the erosive forward movement of the ice contributed to the separation of what is now Long Island and Staten Island. That action left bedrock at a shallow depth, providing a solid foundation for most of Manhattan's skyscrapers. In the precolonial era, the area of present-day New York City was inhabited by Algonquian Native Americans, including the Lenape, whose homeland, known as Lenapehoking, included Staten Island; the first documented visit into New York Harbor by a European was in 1524 by Giovanni da Verrazzano, a Florentine explorer in the service of the French crown. He named it Nouvelle Angoulême. A Spanish expedition led by captain Estêvão Gomes, a Portuguese sailing for Emperor Charles V, arrived in New York Harbor in January 1525 and charted the mouth of the Hudson River, which he named Río de San Antonio.
The Padrón Rea
A diamond cut is a style or design guide used when shaping a diamond for polishing such as the brilliant cut. Cut does not refer to shape, but the symmetry and polish of a diamond; the cut of a diamond affects a diamond's brilliance. In order to best use a diamond gemstone's material properties, a number of different diamond cuts have been developed. A diamond cut constitutes a more or less symmetrical arrangement of facets, which together modify the shape and appearance of a diamond crystal. Diamond cutters must consider several factors, such as the shape and size of the crystal, when choosing a cut; the practical history of diamond cuts can be traced back to the Middle Ages, while their theoretical basis was not developed until the turn of the 20th century. Design creation and innovation continue to the present day: new technology—notably laser cutting and computer-aided design—has enabled the development of cuts whose complexity, optical performance, waste reduction were hitherto unthinkable.
The most popular of diamond cuts is the modern round brilliant, whose facet arrangements and proportions have been perfected by both mathematical and empirical analysis. Popular are the fancy cuts, which come in a variety of shapes, many of which were derived from the round brilliant. A diamond's cut is evaluated by trained graders, with higher grades given to stones whose symmetry and proportions most match the particular "ideal" used as a benchmark; the strictest standards are applied to the round brilliant. Different countries base their cut grading on different ideals: one may speak of the American Standard or the Scandinavian Standard, to give but two examples; the history of diamond cuts can be traced to the late Middle Ages, before which time diamonds were employed in their natural octahedral state—anhedral diamonds were not used in jewelry. The first "improvements" on nature's design involved a simple polishing of the octahedral crystal faces to create and unblemished facets, or to fashion the desired octahedral shape out of an otherwise unappealing piece of rough.
This was called the point cut and dates from the mid 14th century. By the mid 15th century, the point cut began to be improved upon: a little less than one half of the octahedron would be sawn off, creating the table cut; the importance of a culet was realised, some table-cut stones may possess one. The addition of four corner facets created the old single cut. Neither of these early cuts would reveal. At the time, diamond was valued chiefly for its adamantine superlative hardness. For this reason, colored gemstones such as ruby and sapphire were far more popular in jewelry of the era. In or around 1476, Lodewyk van Berquem, a Flemish polisher of Bruges, introduced the technique of absolute symmetry in the disposition of facets using a device of his own invention, the scaif, he cut stones in the shape known as briolette. About the middle of the 16th century, the rose or rosette was introduced in Antwerp: it consisted of triangular facets arranged in a symmetrical radiating pattern, but with the bottom of the stone left flat—essentially a crown without a pavilion.
Many large, famous Indian diamonds of old feature a rose-like cut. However, Indian "rose cuts" were far less symmetrical as their cutters had the primary interest of conserving carat weight, due to the divine status of diamond in India. In either event, the rose cut continued to evolve, with its depth and arrangements of facets being tweaked; the first brilliant cuts were introduced in the middle of the 17th century. Known as Mazarins, they had 17 facets on the crown, they are called double-cut brilliants as they are seen as a step up from old single cuts. Vincent Peruzzi, a Venetian polisher increased the number of crown facets from 17 to 33, thereby increasing the fire and brilliance of the cut gem, properties that in the Mazarin were incomparably better than in the rose, yet Peruzzi-cut diamonds, when seen nowadays, seem exceedingly dull compared to modern-cut brilliants. Because the practice of bruting had not yet been developed, these early brilliants were all rounded squares or rectangles in cross-section.
Given the general name of cushion—what are known today as old mine cuts—these were common by the early 18th century. Sometime the old European cut was developed, which had a shallower pavilion, more rounded shape, different arrangement of facets; the old European cut was the forerunner of modern brilliants and was the most advanced in use during the 19th century. Around 1900, the development of diamond saws and good jewelry lathes enabled the development of modern diamond cutting and diamond cuts, chief among them the round brilliant cut. In 1919, Marcel Tolkowsky analyzed this cut: his calculations took both brilliance and fire into consideration, creating a delicate balance between the two. Tolkowsky's calculations would serve as the basis for all future brilliant cut modifications and standards. Tolkowsky's model of the "ideal" cut is not perfect; the original mo
Geneva is the second-most populous city in Switzerland and the most populous city of Romandy, the French-speaking part of Switzerland. Situated where the Rhône exits Lake Geneva, it is the capital of the Canton of Geneva; the municipality has a population of 200,548, the canton has 495,249 residents. In 2014, the compact agglomération du Grand Genève had 946,000 inhabitants in 212 communities in both Switzerland and France. Within Swiss territory, the commuter area named "Métropole lémanique" contains a population of 1.26 million. This area is spread east from Geneva towards the Riviera area and north-east towards Yverdon-les-Bains, in the neighbouring canton of Vaud. Geneva is a global city, a financial centre, a worldwide centre for diplomacy due to the presence of numerous international organizations, including the headquarters of many agencies of the United Nations and the Red Cross. Geneva hosts the highest number of international organizations in the world, it is where the Geneva Conventions were signed, which chiefly concern the treatment of wartime non-combatants and prisoners of war.
In 2017, Geneva was ranked as the world's fifteenth most important financial centre for competitiveness by the Global Financial Centres Index, fifth in Europe behind London, Zürich and Luxembourg. In 2019 Geneva was ranked among the ten most liveable cities in the world by Mercer together with Zürich and Basel; the city has been referred to as the world's most compact metropolis and the "Peace Capital". In 2017, Geneva was ranked as the seventh most expensive city in the world. Geneva was ranked third in purchasing power in a global cities ranking by UBS in 2018; the city was mentioned in Latin texts, by Caesar, with the spelling Genava from the Celtic *genawa- from the stem *genu-, in the sense of a bending river or estuary. The medieval county of Geneva in Middle Latin was known as pagus major Genevensis or Comitatus Genevensis. After 1400 it became the Genevois province of Savoy; the name takes various forms in modern languages, Geneva in English, French: Genève, German: Genf, Italian: Ginevra, Romansh: Genevra.
The city shares the origin of * genawa "estuary", with the Italian port city of Genoa. Geneva was an Allobrogian border town, fortified against the Helvetii tribe, when the Romans took it in 121 BC, it became Christian under the Late Roman Empire, acquired its first bishop in the 5th century, having been connected to the Bishopric of Vienne in the 4th. In the Middle Ages, Geneva was ruled by a count under the Holy Roman Empire until the late 14th century, when it was granted a charter giving it a high degree of self-governance. Around this time, the House of Savoy came to at least nominally dominate the city. In the 15th century, an oligarchic republican government emerged with the creation of the Grand Council. In the first half of the 16th century, the Protestant Reformation reached the city, causing religious strife, during which Savoy rule was thrown off and Geneva allied itself with the Swiss Confederacy. In 1541, with Protestantism on the rise, John Calvin, the Protestant Reformer and proponent of Calvinism, became the spiritual leader of the city and established the Republic of Geneva.
By the 18th century, Geneva had come under the influence of Catholic France, which cultivated the city as its own. France tended to be at odds with the ordinary townsfolk, which inspired the failed Geneva Revolution of 1782, an attempt to win representation in the government for men of modest means. In 1798, revolutionary France under the Directory annexed Geneva. At the end of the Napoleonic Wars, on 1 June 1814, Geneva was admitted to the Swiss Confederation. In 1907, the separation of Church and State was adopted. Geneva flourished in the 19th and 20th centuries, becoming the seat of many international organizations. Geneva is located at 46°12' North, 6°09' East, at the south-western end of Lake Geneva, where the Rhône flows out, it is surrounded by three mountain chains, each belonging to the Jura: the Jura main range lies north-westward, the Vuache southward, the Salève south-eastward. The city covers an area of 15.93 km2, while the area of the canton is 282 km2, including the two small exclaves of Céligny in Vaud.
The part of the lake, attached to Geneva has an area of 38 km2 and is sometimes referred to as petit lac. The canton has only a 4.5-kilometre-long border with the rest of Switzerland. Of 107.5 km of border, 103 are shared with France, the Département de l'Ain to the north and west and the Département de la Haute-Savoie to the south and east. Of the land in the city, 0.24 km2, or 1.5%, is used for agricultural purposes, while 0.5 km2, or 3.1%, is forested. The rest of the land, 14.63 km2, or 91.8%, is built up, 0.49 km2, or 3.1%, is either rivers or lakes and 0.02 km2, or 0.1%, is wasteland. Of the built up area, industrial buildings made up 3.4%, housing and buildings made up 46.2% and transportation infrastructure 25.8%, while parks, green belts and sports fields made up 15.7%. Of the agricultural land, 0.3% is used for growing crops. Of the water in the municipality, 0.2 % is composed of lakes and 2.9 % streams. The altitude of Geneva is 373.6 metres, corresponds to the altitude of
Duke of Devonshire Emerald
The Duke of Devonshire Emerald is one of the world's largest and most famous uncut emeralds, weighing 1,383.93 carats. Originating in the mine at Muzo, Colombia, it was either gifted or sold by Emperor Pedro I of Brazil to William Cavendish, 6th Duke of Devonshire in 1831, it was displayed at the Great Exhibition in London in 1851, more at the Natural History Museum in 2007. Colombian emeralds Muzo
South Africa the Republic of South Africa, is the southernmost country in Africa. It is bounded to the south by 2,798 kilometres of coastline of Southern Africa stretching along the South Atlantic and Indian Oceans. South Africa is the largest country in Southern Africa and the 25th-largest country in the world by land area and, with over 57 million people, is the world's 24th-most populous nation, it is the southernmost country on the mainland of the Eastern Hemisphere. About 80 percent of South Africans are of Sub-Saharan African ancestry, divided among a variety of ethnic groups speaking different African languages, nine of which have official status; the remaining population consists of Africa's largest communities of European and multiracial ancestry. South Africa is a multiethnic society encompassing a wide variety of cultures and religions, its pluralistic makeup is reflected in the constitution's recognition of 11 official languages, the fourth highest number in the world. Two of these languages are of European origin: Afrikaans developed from Dutch and serves as the first language of most coloured and white South Africans.
The country is one of the few in Africa never to have had a coup d'état, regular elections have been held for a century. However, the vast majority of black South Africans were not enfranchised until 1994. During the 20th century, the black majority sought to recover its rights from the dominant white minority, with this struggle playing a large role in the country's recent history and politics; the National Party imposed apartheid in 1948. After a long and sometimes violent struggle by the African National Congress and other anti-apartheid activists both inside and outside the country, the repeal of discriminatory laws began in 1990. Since 1994, all ethnic and linguistic groups have held political representation in the country's liberal democracy, which comprises a parliamentary republic and nine provinces. South Africa is referred to as the "rainbow nation" to describe the country's multicultural diversity in the wake of apartheid; the World Bank classifies South Africa as an upper-middle-income economy, a newly industrialised country.
Its economy is the second-largest in Africa, the 34th-largest in the world. In terms of purchasing power parity, South Africa has the seventh-highest per capita income in Africa; however and inequality remain widespread, with about a quarter of the population unemployed and living on less than US$1.25 a day. South Africa has been identified as a middle power in international affairs, maintains significant regional influence; the name "South Africa" is derived from the country's geographic location at the southern tip of Africa. Upon formation, the country was named the Union of South Africa in English, reflecting its origin from the unification of four separate British colonies. Since 1961, the long form name in English has been the "Republic of South Africa". In Dutch, the country was named Republiek van Zuid-Afrika, replaced in 1983 by the Afrikaans Republiek van Suid-Afrika. Since 1994, the Republic has had an official name in each of its 11 official languages. Mzansi, derived from the Xhosa noun umzantsi meaning "south", is a colloquial name for South Africa, while some Pan-Africanist political parties prefer the term "Azania".
South Africa contains human-fossil sites in the world. Archaeologists have recovered extensive fossil remains from a series of caves in Gauteng Province; the area, a UNESCO World Heritage site, has been branded "the Cradle of Humankind". The sites include one of the richest sites for hominin fossils in the world. Other sites include Gondolin Cave Kromdraai, Coopers Cave and Malapa. Raymond Dart identified the first hominin fossil discovered in Africa, the Taung Child in 1924. Further hominin remains have come from the sites of Makapansgat in Limpopo Province and Florisbad in the Free State Province, Border Cave in KwaZulu-Natal Province, Klasies River Mouth in Eastern Cape Province and Pinnacle Point and Die Kelders Cave in Western Cape Province; these finds suggest that various hominid species existed in South Africa from about three million years ago, starting with Australopithecus africanus. There followed species including Australopithecus sediba, Homo ergaster, Homo erectus, Homo rhodesiensis, Homo helmei, Homo naledi and modern humans.
Modern humans have inhabited Southern Africa for at least 170,000 years. Various researchers have located pebble tools within the Vaal River valley. Settlements of Bantu-speaking peoples, who were iron-using agriculturists and herdsmen, were present south of the Limpopo River by the 4th or 5th century CE, they displaced and absorbed the original Khoisan speakers, the Khoikhoi and San peoples. The Bantu moved south; the earliest ironworks in modern-day KwaZulu-Natal Province are believed to date from around 1050. The southernmost group was the Xhosa people, whose language incorporates certain linguistic traits from the earlier Khoisan people; the Xhosa reached the Great Fish River, in today's Eastern Cape Province. As they migrated, these larger Iron Age populations