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copyright 2008 cegva israel diamond
Hong Kong Show Room (852) 31732916
Introduction:-
Diamond is the hardest natural material known to man and the third-hardest known material after aggregated diamond nanorods and ultrahard fullerite. Its hardness and high dispersion of light make it useful for industrial applications and jewelry.
Diamonds are specifically renowned as a material with superlative physical qualities — they make excellent abrasives because they can be scratched only by other diamonds, Borazon, ultrahard fullerite, or aggregated diamond nanorods, which also means they hold a polish extremely well and retain their lustre. About 130 million carats (26,000 kg) are mined annually, with a total value of nearly USD $9 billion.[citation needed] About 100,000 kg are synthesized annually.
The name diamond derives from the ancient Greek adamas ("invincible"). They have been treasured as gemstones since their use as religious icons in ancient India and usage in engraving tools also dates to early human history.[3][4] Popularity of diamonds has risen since the 19th century because of increased supply, improved cutting and polishing techniques, growth in the world economy, and innovative and successful advertising campaigns. They are commonly judged by the “four Cs”: carat, clarity, color, and cut.
Roughly 49% of diamonds originate from central and southern Africa, although significant sources of the mineral have been discovered in Canada, India, Russia, Brazil, and Australia. They are mined from kimberlite and lamproite volcanic pipes, which brought to the surface the diamond crystals from deep in the Earth where the high pressure and temperature enables the formation of the crystals.
Diamond mineral, one of two crystalline forms of the element carbon, the hardest natural substance known, used as a gem and in industry.
Diamonds crystallize in the isometric system commonly as transparent to translucent white, colorless, yellow, green, blue, or brown octahedrons (the familiar diamond shape). The extraordinary brilliancy of diamonds after faceting is due to their very high refractive index, which is greater than that of any other naturally occurring gemstone. In addition to the gem varieties there are bort, which is poorly crystallized or of inferior color and in fragmentary condition, and carbonado (black diamond), which is gray to black and opaque, with poor cleavage. Bort and carbonado are used as abrasives, in the cutting of diamonds, and for the cutting heads of rock drills. Diamond abrasives may have been used as early as 2500 BC in China.
How Diamonds Form:-
Diamonds are crystals composed of pure carbon. In nature, diamond crystallizes from hot carbon-rich fluids. This crystallization requires tremendous heat and pressure—1000 to 1200°C (1800 to 2200°F) of heat and 50 kilobars of pressure. (One bar is based on the pressure the atmosphere exerts at sea level, about 1.02 kg per sq cm, or 14.7 lb per sq in; 50 kilobars is 50,000 bars.) The pressures and temperatures at which natural diamond forms only occur deep underground. Scientists believe that diamonds form at depths greater than 150 km (93 mi), and there is evidence that some diamonds formed as deep as 670 km (420 mi) beneath Earth’s surface.
Concentrations of diamonds great enough to be economically feasible for mining are usually found in Earth’s oldest continental regions, called cratons. Cratons form the cores of most continents and consist of inactive geological areas more than 2 billion years old with thick crust and deep roots extending into the mantle beneath. Craton conditions are ideal for diamond formation and preservation. Scientists have determined the ages of some diamonds by dating mineral impurities trapped within the diamonds. These data reveal that most cratonic diamonds are ancient, some older than 3 billion years.
Much younger volcanic rocks—kimberlites and lamproites—pass through the cratonic rocks in a liquid form called magma during their rapid ascent to Earth’s surface. These flowing veins of rock act as carriers of diamonds and other rock fragments. After eruption they solidify, forming funnel-shaped kimberlite “pipes.” These pipes are primary diamond deposits. Many diamonds are recovered at a distance from their primary deposits in secondary alluvial deposits, which are loose eroded materials left behind by flowing water. In some instances diamonds are also found in sandstones, conglomerates, and other sedimentary rocks that presumably solidified from former alluvial deposits. Wind and glaciers can also transport diamonds from their point of origin at Earth’s surface.
Small, generally low quality diamonds form in rocks at shallower depths under pressure conditions that are higher than usual for those depths. Tectonic movement, rather than magma, transports these diamonds to Earth’s surface. Deposits of this type occur in areas such as Kazakhstan and typically involve the collision of a continental and an oceanic plate followed by rapid uplift of deeply buried rocks. Diamond deposits brought to the surface by tectonic movement are generally younger than kimberlitic diamonds, and typically consist of microdiamonds (less than 1 mm across) or graphite relics of larger diamonds.
Diamonds are also found in meteorites and near meteorite craters on Earth’s surface. Extremely small diamonds (nanodiamonds) occur in many types of meteorites and have a lower density than other diamonds. Meteorites can also produce pressure and heat at the moment of impact sufficient to transform carbon into diamond. Diamond found in a type of meteorite called ureilite is thought to form directly from graphite contained in the meteorites upon impact. Impact-crater diamonds are opaque and range from very small to around a centimeter in diameter.
Black diamonds called carbonados are thought to have an extraterrestrial origin, as well. These diamonds are only found in 1.5-billion-year-old geologic formations in Brazil and in the Central African Republic, regions that were connected as part of one land mass at the time. Carbonados are not associated with volcanic rock or other types of diamonds. A study published in 2006 established that their chemistry is unlike that of diamonds formed on Earth. Infrared analysis of the carbonado samples indicated that the minerals may have formed in a supernova explosion between 2.6 billion to 3.8 billion years ago. The black diamonds might have come to Earth inside meteorites.
Natural Occurrence and Processing:- Diamonds are found in alluvial (loose earthy material deposited by running water) formations and in volcanic pipes, filled for most of their length with blue ground or kimberlite, an igneous rock consisting largely of serpentine . At the surface the blue ground is weathered to a clay called yellow ground. Diamantiferous (or diamondiferous), or diamond-yielding, earth is mined both by the open-pit method and by underground mining. After being removed to the surface, it is crushed and then concentrated. Sorting is done by passing the concentrated material in a stream of water over greased tables. The diamond, being largely water repellent, sticks to the grease, but the other minerals retain a film of water, which prevents them from adhering to the grease. The diamonds are then removed from the grease, cleaned, and graded for sale.
Sources:-
The earliest sources of gem diamonds were India and Borneo, where they were found in river alluvium. All famous diamonds of antiquity were Indian diamonds, including the Great Mogul, the Orlov, the Koh-i-noor, and the Regent or Pitt. Other famous diamonds are the Hope (blue), Dresden (green). In the early 18th cent., deposits similar to those in India were found in Brazil, mainly of carbonados, though they may have been known as early as 1670. In 1867, a stone found in South Africa was recognized as a diamond. Within a few years, this began a wild search for diamonds, both in river diggings and inland. In 1870-71, dry diggings, including most of the celebrated mines, were discovered. Well-known South African diamond mines are the Dutoitspan, Bultfontein, De Beers, Kimberley, Jagersfontein, and Premier. Botswana, Namibia, Cananda, and South Africa are now the world's major diamond-producing nations; other important countries include Australia, Russia, Brazil, Angola, Sierra Leon
e, Ghana, Tanzania, and Venezuela. The use of diamonds to finance African rebel groups and fuel civil strife in the 1990s led, in 2001 and 2002, to international agreements (the Kimberly Process) designed to certify legitimately mined diamonds, but so-called blood diamonds remain a source of financing for the conflict in Cote d'Ivoire.
Synthetic diamonds were successfully produced in 1955; a number of small crystals were manufactured when pure graphite mixed with a catalyst was subjected to pressure of about 1 million lb per sq in. and temperature of the order of 5,000°F (3,000°C). Synthetic diamonds are now extensively used in industry.
The Diamond Cartel:-The discoveries of 1870-71 in South Africa led to a great number of prospectors staking out claims and securing the diamonds by open-pit or quarry mining. The damage caused by floods and mudslides, unavoidable when there were so many different claims, was an important factor in the series of amalgamations carried on by Cecil Rhodes and Barnett Barnato . Rhodes brought about the merging of their interests in the De Beers Consolidated Mines, Ltd., which established (1889) an effective monopoly over the diamond industry. Loss of diamonds by theft was reduced through the passage of the so-called I.D.B. (Illicit Diamond Buying) Act, which limited the trade to licensed buyers and imposed penalties for the possession of uncut stones without a license. Thefts were further curtailed by the institution of compounds in which the workers live while employed by the company and which they leave only after being thoroughly searched.
Most of the major diamond producers belong to, or have cooperated with, the De Beers-led marketing cartel, formed to maintain the price of diamonds at a high level. De Beers, under Harry Oppenheimer's leadership (1957-84), maintained its dominant position in the industry by using its numerous worldwide companies to buy up new sources of diamonds and to control distribution of industrial diamonds and production of synthetic ones. In the last decades of the 20th cent., however, De Beers' hold over the unpolished diamond market decreased, and in 2000 the company announced it would end to its policy of controlling diamond prices through hoarding and shift its focus to increasing sales.
A diamond's optical performance is the visual interaction of the diamond reflecting and refracting surrounding light to the viewer. It is this performance of the diamond that results in its beauty. This work advances the idea that the best diamond cuts 'evolved' to have the highest optical performance in a variety of typical viewing and illumination circumstances.
Properties:-
Diamond is the hardest natural substance known. This hardness is exhibited in diamond’s resistance to scratching and its ability to scratch other materials. Steel and glass, for instance, can be scratched by diamond. The Mohs hardness scale, devised by the German mineralogist Friedrich Mohs to indicate relative hardness of substances on a rating scale from 1 to 10, assigns diamond a value of 10. Diamond’s hardness is not a constant quantity but varies even within a single diamond.
Diamonds are crystals composed of carbon atoms. Atoms in a crystal are arrayed in a regular repeating pattern. A crystal’s outward form, bounded by smooth plane surfaces that meet at predictable angles, reflects this internal order. Crystals tend to cleave, or split, along lines called cleavage planes between layers of atoms. In the case of diamond crystals, each carbon atom is bonded to four surrounding carbon atoms. This microscopic arrangement determines the visible shape of diamond crystals, which are generally octahedrons (solid shapes with eight faces). Individual diamond crystals therefore cleave cleanly along planes parallel to the faces of an octahedron.
Two important properties, brilliance and fire, contribute to diamond’s beauty. Brilliance is the fraction of the light that falls on a diamond that the diamond returns to the eyes of an observer—the more light returned, the higher the brilliance. Diamond’s brilliance arises from its index of refraction, which determines the angle at which light is bent as it crosses the boundary between the air and the stone. Fire is the ability of a substance to split white light into rainbow colors—the greater the separation between colors, the greater the fire. Diamond’s fire originates with its dispersion, which is the difference in diamond’s index of refraction for light of different colors. Diamond has both a higher index of refraction and a higher dispersion value than any other natural, transparent, colorless material.
Diamonds exhibit a wide range of transparency and color. Transparency is a measure of the amount of light that passes through a diamond rather than being absorbed. Colorless diamonds, known as white diamonds, are most familiar, but green, blue, red, orange, yellow, and brown diamonds also are known. Structural imperfections or dislocations and the presence of trace elements, mainly nitrogen, cause color in diamonds. Some diamonds luminesce (emit light) when exposed to sunlight or other ultraviolet-light sources. The light the diamonds emit is usually light blue, but yellow, orange, and red luminescence occurs in some stones.
Most diamonds used as gems are single crystals large enough to be easily visible to the eye. Diamond also occurs, however, in polycrystalline forms commonly known as ballas, bort, and carbonado. Ballas is a compact, spherical mass of tiny diamond crystals of great hardness and toughness. Bort is an extremely hard, dark, imperfectly crystallized diamond. The term bort sometimes is also applied to minute fragments of gem diamonds. Carbonado is an opaque grayish or black form of diamond that consists of microscopic crystals and has no cleavage. Ballas, bort, and carbonado are all used industrially, in lapidary (gem-cutting) work, and as a tough coating for the tips of drills and the edges of cutting tools.
Other characteristics of diamonds are frequently useful in identifying the stones and in differentiating between true diamonds and imitations. Because diamonds are excellent conductors of heat, they are cold to the touch and are sometimes called “ice.” Most diamonds do not conduct electricity well, but diamonds do become charged with positive static electricity when rubbed. Diamond resists attack by acids or bases. Since diamonds are a form of carbon, like coal, they will burn, but only when heated to extremely high temperatures.
The density of diamond ranges between 3.15 and 3.53 g/cm3, but the density of pure diamond is always very close to 3.52 g/cm3. Diamond is much denser than crystals composed of elements of similar weight to carbon atoms because the carbon atoms in diamond are packed tightly together. Quartz, for example, is composed of atoms of silicon and oxygen, both of which are heavier than carbon atoms. The density of quartz, however, is only 2.65 g/cm3.
Diamond Cutting:- Rough diamonds are not brilliant and can appear greasy. Diamond cutting encompasses a number of processes that bring out the beauty of gem diamonds. These processes include cleaving, sawing or laser cutting, and polishing. A diamond cutter seeks to enhance the brilliance and fire of each stone and to eliminate imperfections, such as cracks and cloudiness. The cutter develops a plan that will accomplish these goals while still producing a gem of the greatest size and hence maximum value. About half of a natural diamond’s size is lost in diamond cutting.
Examining the stone is the first step in diamond cutting. The cutter determines where cleavage planes lie and decides how the stone can best be divided by cleaving and sawing. Ink marks on the rough diamond serve as a guide for the shaping to follow.
The cutter next places the diamond firmly in a holder for cleaving. A light blow of a hammer on the cleaving iron, which is held against the diamond parallel to the cleavage plane, cleaves the stone. In present-day practice cutters more often saw diamonds or cut them with a laser rather than cleave them. The saw is a thin metal disk, the edge of which is impregnated with a mixture of diamond dust and oil.
Polishing, the final step in the cutting of a diamond, consists of forming the facets of the finished stone. Cutters most often choose the “brilliant” form, which has 58 facets. During the polishing process a mount called a dop firmly holds the gem. A flat, horizontally revolving cast-iron wheel coated with a mixture of diamond dust and oil forms the facets. The cutter holds the stone in its dop against the surface of the wheel until the facet forms. In the course of polishing, the cutter moves the stone many times in its dop to present new surfaces for polishing.
Judging a Diamond’s Quality:- Only high-quality diamonds are suitable for use as gems. In judging the quality (and therefore the value) of a cut diamond, a buyer must take into account four criteria, known as the “four C’s”: color, clarity, carat weight, and cut. Colorless stones are extremely valuable, while yellow or brown-tinged stones are regarded as imperfect. Fancy, colored diamonds, or fancies, exhibit clear, strong colors such as blue, green, red, and orange. Fancies are quite rare and highly prized. The presence or absence of internal blemishes and flaws determines clarity. Weight reflects a diamond’s size. The unit of weight usually employed for diamonds and other gems is the metric carat, which is equal to 0.2 g (about 0.007 oz). Another unit used to express the weight of diamonds is the point, equal to 0.01 carat. A stone of 82 points would therefore weigh 0.82 carat. A 5-carat stone is worth more than five 1-carat stones that are otherwise of the same quality. The final criteria buyers use in det
ermining the quality of a diam ond is its cut. The cut is the shape and proportion of the stone, as determined during the diamond-cutting procedure.
Industrial Uses:-
Eighty percent of natural diamonds produced from mining contain flaws with regard to color, shape, or size or have impurities that make them unsuitable for use as gems. Ballas, bort, and carbonado are examples of flawed diamonds. Such diamonds are classed as industrial grade and used in manufacturing.
Due to its hardness, diamond, as either single crystals or finely ground powder, can be used in cutting, abrading, or polishing tools. It is used extensively in drill bits, in cutting devices, and as a surface that can withstand shock and pressure. Industrial diamond has applications in the mining, oil and gas, electronic, optical, thermal, machining, dentistry, and medical industries. Scientific applications include radiation- and photo-detection and experiments involving high pressures and temperatures.
Synthetic and Imitation Diamond:- High demand for diamonds has led to the development of methods for producing artificial diamonds. Artificial diamonds used in industry are generally known as synthetic diamonds; artificial diamonds used for ornamentation are called imitation diamonds. Even though the majority of natural diamonds are industrial grade, only about 10 percent of the diamonds used for industrial purposes are natural diamonds. The other 90 percent are synthetic. The two most common processes of synthesizing diamond are the high-temperature high-pressure (HTHP) and chemical vapor deposition (CVD) methods. The HTHP method converts carbon to diamond at high temperature and pressure using a molten metal catalyst. The HTHP method is sometimes also used to change or enhance the colors of some rare natural diamonds, thus making them more valuable on the market. The CVD method produces diamond coatings by heating a hydrocarbon gas over a metal surface. These diamond coatings greatly extend the lifetimes of
precision dies, drills, and saw b lades. The high price of gem diamonds has created a market for imitation diamonds made from less expensive materials. Minerals that strongly disperse light, including cubic zirconia, transparent quartz (rock crystal), synthetic rutile, corundum, spinel, and moissanite (silicon carbide), are all used as imitation diamonds. Other imitations are made from a lead glass known as paste or strass. Devices called thermal conductivity probes can detect imitation diamonds because imitation diamonds generally do not conduct heat as well as real diamonds. Imitation diamonds can also be identified optically and are easily scratched by real diamond.
History:-
The word diamond is derived from the ancient Greek term adamas meaning “invincible,” which the ancient Greeks probably applied to any hard stone. Sanskrit texts from India contain one of the earliest references to diamonds and suggest that diamonds were known and ascribed value at some time before 400 bc.
Roman literature of the 1st century ad contains another early reference to diamond, and the diamonds known to the Romans undoubtedly came from India. India was for centuries the greatest source of diamonds in the world and is known for most of the famous historical diamonds. Although diamonds discovered in Borneo around 700 ad were an important source for Southeast Asia, India was the only source of diamonds known to Europeans until the 18th century. Europeans believed that diamonds were found only in the fabled mines of Golconda, near present-day Hyderabad. Golconda was in fact the market city of the diamond trade, and gems sold there came from a number of mines.
The earliest evidence of diamond cutting dates to the 1330s in Venice. Europeans began to trade diamonds on a regular basis early in the 15th century with the opening of trade routes to the east. A second source for Europeans became available when diamonds were discovered in Brazil in 1726. The Brazilian diamond trade is the world’s main producer of ballas and carbonado.
The identification of a “pebble” picked up by a child on the banks of the Orange River in South Africa in 1866 as a 21-carat diamond precipitated the opening of diamond fields in that region. The rush to search for alluvial diamonds in the gravel of the Orange and Vaal rivers greatly accelerated in 1870 and 1871 following the discovery of “dry diggings” in the district near present-day Kimberley. These diggings were roughly circular patches of yellow clay containing diamonds. As the miners dug deeper in the clay, often called “yellow ground,” they found a hard, bluish rock below it that also proved to be productive. This “blue ground,” a rock called kimberlite, is the parent material from which yellow ground is formed by weathering. Further mining disclosed that the circular areas of yellow and blue ground are the tops of funnel-shaped volcanic pipes of kimberlite. Prospectors have found similar pipes, not all of which contain diamonds, at various other locations in Africa and other continents.
South Africa quickly became the leading producer of diamonds in the world. During the late 19th century De Beers Consolidated Mines Ltd., led by British colonial statesman Cecil Rhodes, was formed there. To this day the De Beers cartel controls a large portion of the world’s natural diamond production.
South Africa is still a leading producer of diamonds, but prospectors have found substantial diamond deposits, many of which are alluvial, in other parts of Africa, including Botswana, the Democratic Republic of the Congo (DRC, formerly Zaire), Tanzania, Ghana, and Sierra Leone. Other major present-day diamond producers are Australia, Siberia in Russia, Brazil, Venezuela, and Guyana. Canada may become a large diamond producer in the near future due to the discovery of diamond deposits in the Northwest Territories and Alberta during the mid- and late 1990s.
Smaller natural diamond deposits occur in China, Borneo, Myanmar, Thailand, and the Ural Mountains in Russia. Isolated stones have been found at various places in the United States, and a kimberlite pipe on the Colorado-Wyoming state line yields sufficient quantities for mining. Kimberlite diamonds also occur in Arkansas.
General Electric produced the first small synthetic diamonds of similar quality to natural industrial diamonds in 1955. Today, industrial-grade synthetic diamonds are inexpensively mass-produced.
Since the 1990s international concern has grown over “conflict” or “blood” diamonds. In parts of Africa, illicit trade in rough diamonds has been used to finance and arm rebel forces and terrorist groups. Vicious civil wars involving Angola, Sierra Leone, Liberia, the Democratic Republic of Congo, and Cote d’Ivoire have been linked to the sale of such diamonds. Millions of dollars earned from “blood” diamonds have been used to purchase weapons and military equipment that can prolong and worsen conflicts. In addition, the demand for such diamonds can encourage corruption, as well as labor and human rights abuses. One of the worst cases combining such situations occurred in Sierra Leone. The Revolutionary United Front (RUF) tried to overthrow the government with funding and arms from diamond sales. The RUF carried out a reign of terror in which thousands of civilians had their hands and other body parts chopped off. The RUF also brutalized the prisoner-laborers they used to dig raw diamonds from open-pit mines.
Profits from the smuggling of conflict diamonds also may have benefited al-Qaeda, according to some sources.
Once such illicit diamonds enter the international gem market, they are almost impossible to trace to their source. Human rights groups such as Amnesty International, Global Witness, and Global Exchange have worked to raise awareness of the issue. The United Nations passed a resolution in 2000 that called for “certificates of origin” to ensure that rough diamonds come from legitimate and legal sources. In 2002 a large number of countries, including the United States, approved the Kimberley Process designed to end the trafficking of illicit diamonds. As of 2006, 71 countries had joined the system of certification. Enforcement of the Kimberley Process has been difficult or weak, however, and the smuggling of such diamonds allegedly continues in some countries.
Famous Diamonds:- A number of individual diamonds have become famous, primarily for their great size but also for their exceptional color, cut, uniqueness, or history. The Great Mogul diamond, reputed to have weighed 240 carats when cut, has disappeared since it was described by the French traveler Jean Baptiste Tavernier in India in 1665. Some authorities believe that the Koh-i-noor diamond, which now weighs 106.1 carats and is one of the British crown jewels, was part of the Great Mogul. Jean Baptiste Tavernier is also associated with the Hope diamond, a 45.52-carat blue diamond that originally weighed 110.5 carats. The Hope diamond is a recut version of the Great Blue diamond. The Great Blue diamond was once part of the French crown jewels.
The Cullinan, the largest rough diamond ever found, was discovered in the Premier Mine in South Africa in 1905. The government of the Transvaal, a British crown colony that later became part of the Union of South Africa, presented the Cullinan to King Edward VII. The Cullinan weighed 3,106 carats (1.37 lb) before cutting and was pronounced by crystallographers to be a cleavage fragment of a considerably larger stone. When the stone was cut a total of 105 gems were produced weighing 1,063 carats in all. The largest of these was a 530.2-carat drop-shaped stone called the Star of Africa or Cullinan I. The Star of Africa is the second largest cut diamond in existence and is set in the British royal scepter. The largest known cut diamond is a yellowish-brown stone called the Golden Jubilee. It was given to the King of Thailand in 1997 to honor the 50th anniversary of his coronation.
The Vargas diamond, found in Brazil in 1938, weighed 726.6 carats in its uncut state. When cut in 1945, it yielded 29 stones with a total weight of 411 carats. In 1934 a diamond of almost precisely the same weight, the Jonker diamond, was discovered in an alluvial deposit near the Premier Mine. The Jonker is the finest-quality large diamond ever found. It was cut into 12 gems ranging from 125.4 to 5.3 carats in weight. In 1967 the Lesotho diamond was discovered, also in South Africa. It weighed 601.3 carats uncut.
The Israeli Diamond Industry is based on a tradition that goes back hundreds of years. It prides itself on its skillfulness and uniqueness as well as its unprecedented creativity and cutting-edge technology. It adheres to a strict ethical code and offers buyers a wide variety of merchandise and services all under one roof. Raw materials and increased diamond manufacturing in the Far East due to inexpensive costs. Both of these challenges can be overcome with the help of sophisticated innovations that will make manufacture in Israel less expensive. The latter, which already exist, will enable innovative diamond processing. To achieve these goals, out-of-the-box machinery and processes must be developed.
While other countries produced small cut diamonds initially, Israel soon became the top producers of large diamonds and fancy, unique cuts. Tel Aviv is probably the most technologically advanced diamond cutting center and exports around $4 billion worth of fancy diamonds.
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