Central African Republic
The Central African Republic is a landlocked country in Central Africa. It is bordered by Chad to the north, Sudan to the northeast, South Sudan to the east, the Democratic Republic of the Congo to the south, the Republic of the Congo to the southwest and Cameroon to the west; the CAR covers a land area of about 620,000 square kilometres and had an estimated population of around 4.6 million as of 2016. The C. A. R. is the scene of a civil war, ongoing since 2012. Most of the CAR consists of Sudano-Guinean savannas, but the country includes a Sahelo-Sudanian zone in the north and an equatorial forest zone in the south. Two thirds of the country is within the Ubangi River basin, while the remaining third lies in the basin of the Chari, which flows into Lake Chad. What is today the Central African Republic has been inhabited for millennia. After gaining independence from France in 1960, the Central African Republic was ruled by a series of autocratic leaders, including an abortive attempt at a monarchy.
Ange-Félix Patassé became president, but was removed by General François Bozizé in the 2003 coup. The Central African Republic Bush War began in 2004 and, despite a peace treaty in 2007 and another in 2011, civil war resumed in 2012, still ongoing. Despite its significant mineral deposits and other resources, such as uranium reserves, crude oil, diamonds, cobalt and hydropower, as well as significant quantities of arable land, the Central African Republic is among the ten poorest countries in the world, with the lowest GDP per capita at purchasing power parity in the world as of 2017; as of 2015, according to the Human Development Index, the country had the lowest level of human development, ranking 188th out of 188 countries. It is estimated to be the unhealthiest country as well as the worst country in which to be young; the Central African Republic is a member of the United Nations, the African Union, the Economic Community of Central African States, the Organisation internationale de la Francophonie and the Non-Aligned Movement.
10,000 years ago, desertification forced hunter-gatherer societies south into the Sahel regions of northern Central Africa, where some groups settled. Farming began as part of the Neolithic Revolution. Initial farming of white yam progressed into millet and sorghum, before 3000 BC the domestication of African oil palm improved the groups' nutrition and allowed for expansion of the local populations; this Agricultural Revolution, combined with a "Fish-stew Revolution", in which fishing began to take place, the use of boats, allowed for the transportation of goods. Products were moved in ceramic pots, which are the first known examples of artistic expression from the region's inhabitants; the Bouar Megaliths in the western region of the country indicate an advanced level of habitation dating back to the late Neolithic Era. Ironworking arrived in the region around 1000 BC from both Bantu cultures in what is today Nigeria and from the Nile city of Meroë, the capital of the Kingdom of Kush. During the Bantu Migrations from about 1000 BC to AD 1000, Ubangian-speaking people spread eastward from Cameroon to Sudan, Bantu-speaking people settled in the southwestern regions of the CAR, Central Sudanic-speaking people settled along the Ubangi River in what is today Central and East CAR.
Bananas added an important source of carbohydrates to the diet. Production of copper, dried fish, textiles dominated the economic trade in the Central African region. During the 16th and 17th centuries slave traders began to raid the region as part of the expansion of the Saharan and Nile River slave routes, their captives were enslaved and shipped to the Mediterranean coast, Arabia, the Western Hemisphere, or to the slave ports and factories along the West and North Africa or South the Ubanqui and Congo rivers. In the mid 19th century, the Bobangi people became major slave traders and sold their captives to the Americas using the Ubangi river to reach the coast. During the 18th century Bandia-Nzakara peoples established the Bangassou Kingdom along the Ubangi River. In 1875, the Sudanese sultan Rabih az-Zubayr governed Upper-Oubangui, which included present-day CAR; the European invasion of Central African territory began in the late 19th century during the Scramble for Africa. Europeans the French and Belgians, arrived in the area in 1885.
France seized and colonized Ubangi-Shari territory in 1894. In 1911 at the Treaty of Fez, France ceded a nearly 300,000 km² portion of the Sangha and Lobaye basins to the German Empire which ceded a smaller area to France. After World War I France again annexed the territory. Modeled on King Leopold's Congo Free State, concessions were doled out to private companies that endeavored to strip the region's assets as and cheaply as possible before depositing a percentage of their profits into the French treasury; the concessionary companies forced local people to harvest rubber and other commodities without pay and held their families hostage until they met their quotas. Between 1890, a year after the French first arrived, 1940, the population declined by half due to diseases and exploitation by private companies. In 1920 French Equatorial Africa was established and Ubangi-Shari was
Carbonado known as the "black diamond", is the toughest form of natural diamond. It is an impure form of polycrystalline diamond consisting of diamond and amorphous carbon, it is found in alluvial deposits in the Central African Republic and in Brazil. Its natural colour is black or dark grey, it is more porous than other diamonds. Carbonado diamonds are pea-sized or larger porous aggregates of many tiny black crystals; the most characteristic carbonados have been found only in the Central African Republic and in Brazil, in neither place associated with kimberlite, the source of typical gem diamonds. Lead isotope analyses have been interpreted as documenting crystallization of carbonados about 3 billion years ago; the carbonados are found in younger sedimentary rocks. Mineral grains included within diamonds have been studied extensively for clues to diamond origin; some typical diamonds contain inclusions of common mantle minerals such as pyrope and forsterite, but such mantle minerals have not been observed in carbonado.
In contrast, some carbonados do contain inclusions of minerals characteristic of the Earth's crust: these inclusions do not establish formation of the diamonds in the crust, because while these obvious crystal inclusions occur in the pores that are common in carbonados, they may have been introduced after carbonado formation. Inclusions of other minerals, rare or nearly absent in the Earth's crust, are found at least incorporated in diamond, not just in pores: among such other minerals are those with compositions of Si, SiC, Fe‑Ni. No distinctive high-pressure minerals, including the hexagonal carbon polymorph, have been found as inclusions in carbonados, although such inclusions might be expected if carbonados formed by meteorite impact. Isotope studies have yielded further clues to carbonado origin; the carbon isotope value is low. Carbonado exhibits strong luminescence induced by nitrogen and by vacancies existing in the crystal lattice. Luminescence halos are present around radioactive inclusions, it is suggested that the radiation damage occurred after formation of the carbonados, an observation pertinent to the radiation hypothesis listed below.
The origin of carbonado is controversial. Some proposed hypotheses are as follows: Direct conversion of organic carbon under high-pressure conditions in the Earth's interior, the most common hypothesis for diamond formation Shock metamorphism induced by meteoritic impact at the Earth's surface Radiation-induced diamond formation by spontaneous fission of uranium and thorium Formation inside an earlier-generation giant star in our area, that long ago exploded in a supernova. An origin in interstellar space, due to the impact of an asteroid, rather than being thrown from within an exploding star. None of these hypotheses for carbonado formation had come into wide acceptance in the scientific literature by 2008. Supporters of an extraterrestrial origin of carbonados propose that their material source was a supernova which occurred at least 3.8 billion years ago. After coalescing and drifting through outer space for about one and a half billion years, a large mass fell to earth as a meteorite 2.3 billion years ago.
It fragmented during entry into the Earth's atmosphere and impacted in a region which would much split into Brazil and the Central African Republic, the only two known locations of carbonado deposits. Amsterdam Diamond Bort Korloff Noir Material properties of diamond Popigai diamonds Sergio Spirit of de Grisogono Diamond Superhard material Photo of porous carbonado at National Science Foundation Photo of glossy carbonado and article on possible extraterrestrial origins at PBS Nova Mystery Diamonds: Geoscientists Investigate Rare Carbon Formation ScienceDaily Story Diamonds From Outer Space: Geologists Discover Origin Of Earth's Mysterious Black Diamonds ScienceDaily Story
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
A chemically pure and structurally perfect diamond is transparent with no hue, or color. However, in reality no gem-sized natural diamonds are perfect; the color of a diamond may be affected by chemical impurities and/or structural defects in the crystal lattice. Depending on the hue and intensity of a diamond's coloration, a diamond's color can either detract from or enhance its value. For example, most white diamonds are discounted in price when more yellow hue is detectable, while intense pink diamonds or blue diamonds can be more valuable. Of all colored diamonds, red diamonds are the rarest; the Aurora Pyramid of Hope displays a spectacular array of colored diamonds, including red diamonds. Diamonds occur in a variety of colors—steel gray, blue, orange, green, pink to purple and black. Colored diamonds contain interstitial impurities or structural defects that cause the coloration, pure diamonds are transparent and colorless. Diamonds are scientifically classed into two main types and several subtypes, according to the nature of impurities present and how these impurities affect light absorption: Type I diamonds have nitrogen atoms as the main impurity at a concentration of 0.1%.
If the nitrogen atoms are in pairs they do not affect the diamond's color. If the nitrogen atoms are in large even-numbered aggregates they impart a yellow to brown tint. About 98% of gem diamonds are type Ia, most of these are a mixture of IaA and IaB material: these diamonds belong to the Cape series, named after the diamond-rich region known as Cape Province in North Africa, whose deposits are Type Ia. If the nitrogen atoms are dispersed throughout the crystal in isolated sites, they give the stone an intense yellow or brown tint. Synthetic diamond containing nitrogen is Type Ib. Type I diamonds absorb from 320 nm, they have a characteristic fluorescence and visible absorption spectrum. Type II diamonds have no measurable nitrogen impurities. Type II diamonds absorb in a different region of the infrared, transmit in the ultraviolet below 225 nm, unlike Type I diamonds, they have differing fluorescence characteristics, but no discernible visible absorption spectrum. Type IIa diamond can be colored pink, red, or brown due to structural anomalies arising through plastic deformation during crystal growth—these diamonds are rare, but constitute a large percentage of Australian production.
Type IIb diamonds, which account for 0.1% of gem diamonds, are light blue due to scattered boron within the crystal matrix. However, a blue-grey color may occur in Type Ia diamonds and be unrelated to boron. Not restricted to type are green diamonds, whose color is caused by GR1 color centers in the crystal lattice produced by exposure to varying quantities of radiation. Pink and red are caused by plastic deformation of the crystal lattice from pressure. Black diamonds are caused by microscopic black or gray inclusions of other materials such as graphite or sulfides and/or microscopic fractures. Opaque or opalescent white diamonds are caused by microscopic inclusions. Purple diamonds are caused by a combination of high hydrogen content; the majority of diamonds that are mined are in a range of pale yellow or brown color, termed the normal color range. Diamonds that are of intense yellow or brown, or any other color are called fancy color diamonds. Diamonds that are of the highest purity are colorless, appear a bright white.
The degree to which diamonds exhibit body color is one of the four value factors by which diamonds are assessed. Diamonds have a color grading system; this system goes from D to Z. The more colorless a diamond is, the rarer and more valuable it is because it appears white and brighter to the eye. Color grading of diamonds was performed as a step of sorting rough diamonds for sale by the London Diamond Syndicate; as the diamond trade developed, early diamond grades were introduced by various parties in the diamond trade. Without any co-operative development these early grading systems lacked standard nomenclature, consistency; some early grading scales were. Numerous terms developed to describe diamonds of particular colors: golconda, jagers, blue white, fine white, gem blue, etc. Refers to a grading scale for diamonds in the normal color range used by internationally recognized laboratories; the scale ranges from D, colorless to Z, a pale yellow or brown color. Brown diamonds darker than K color are described using their letter grade, a descriptive phrase, for example M Faint Brown.
Diamonds with more depth of color than Z color fall into the fancy color diamond range. Diamond color is graded by comparing a sample stone to a master stone set of diamonds; each master stone is known to exhibit the least amount of body color that a diamond in that color grade may exhibit. A trained diamond grader compares a diamond of unknown grade against the series of master stones, assessing where in the range of color the diamond resides; this process occurs in a lighting box, fitted with daylight equivalent lamps. Accurate color grading can only be performed with diamond unset, as the comparison with master