In mineralogy, diamond (from the ancient Greek ἀδάμας, adámas) is the allotrope 
of carbon where the carbon atoms are arranged in an isometric-hexoctahedral crystal lattice. After graphite, diamond is the second most stable form of carbon. Its hardness and high dispersion of light make it useful for industrial applications and jewelry. It is the hardest known naturally occurring mineral. It is possible to treat regular diamonds under a combination of high pressure and high temperature to produce diamonds that are harder than the diamonds used in hardness gauges.[2]
Diamonds are specifically renowned as a material with superlative physical qualities; they make excellent abrasives because few substances can scratch them. As a result they hold a polish extremely well and retain their lustre. Approximately 130 million carats (26,000 kg (57,000 lb)) are mined annually, with a total value of nearly USD $9 billion, and about 100,000 kg (220,000 lb) are synthesized annually.[3]
History
See also: Diamond (gemstone)
Diamonds have been treasured as gemstones since their use as religious icons in ancient India. Their usage in engraving tools also dates to early human history.[4][5] 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.
Diamonds are thought to have been first recognized and mined in India, where significant alluvial deposits of the stone could then be found many centuries ago along the rivers Penner, Krishna and Godavari. Diamonds have been known in India for at least 3000 years but most likely 6000 years.[6]
The name diamond is derived from the ancient Greek ἀδάμας (adámas), "unbreakable, untamed", from ἀ- (a-), "un-" + δαμάω (damáō), "I overpower, I tame"[7], and is the real-world origin of myths about a superhard metal called adamant.
In 1813, Humphry Davy used a lens to concentrate the rays of the sun on a diamond in an atmosphere of oxygen, and showed that the only product of the combustion was carbon dioxide, proving that diamond is composed of carbon.[8] Later, he showed that in an atmosphere devoid of oxygen, diamond is converted to graphite.
The most familiar usage of diamonds today is as gemstones used for adornment, a usage which dates back into antiquity. The dispersion of white light into spectral colors, is the primary gemological characteristic of gem diamonds.
In the twentieth century, experts in the field of gemology have developed methods of grading diamonds and other gemstones based on the characteristics most important to their value as a gem. Four characteristics, known informally as the four Cs, are now commonly used as the basic descriptors of diamonds: these are carat, cut, color, and clarity.
Material properties
Main article: Material properties of diamond
Diamond and g
raphite are two allotropes of carbon: pure forms of the same element that differ in structure.
A diamond is a transparent crystal of tetrahedrally bonded carbon atoms (sp3) that crystallizes into the face centered cubic diamond lattice structure. Diamonds have been adapted for many uses because of the material's exceptional physical characteristics. Most notable are its extreme hardness, its high dispersion index, and extremely high thermal conductivity (900 – 2320 W/m K). Above 1700 °C (1973 K / 3583 °F), diamond is converted to graphite.[9] Naturally occurring diamonds have a density ranging from 3.15 to 3.53 g/cm³, with very pure diamond typically extremely close to 3.52 g/cm³.
Hardness
Diamond is the hardest natural material known, where hardness is defined as resistance to scratching.[10] Diamond has a hardness of 10 (hardest) on Mohs scale of mineral hardness.[11] Diamond's hardness has been known since antiquity, and is the source of its name.
The hardest diamonds in the world are from the Copeton and Bingara fields located in the New England area in New South Wales, Australia. They were called can-ni-fare (cannot be cut) by the cutters in Antwerp when they started to arrive in quantity from Australia in the 1870s. These diamonds are generally small, perfect to semiperfect octahedra, and are used to polish other diamonds. Their hardness is considered to be a product of the crystal growth form, which is single stage growth crystal. Most other diamonds show more evidence of multiple growth stages, which produce inclusions, flaws, and defect planes in the crystal lattice, all of which affect their hardness.[12]
The hardness of diamonds contributes to its suitability as a gemstone. Because it can only be scratched by other diamonds, it maintains its polish extremely well. Unlike many other gems, it is well-suited to daily wear because of its resistance to scratching—perhaps contributing to its popularity as the preferred gem in engagement or wedding rings, which are often worn every day.
Industrial use of diamonds has historically been associated with their hardness; this property makes diamond the ideal material for cutting and grinding tools. As the hardest known naturally-occurring material, diamond can be used to polish, cut, or wear away any material, including other diamonds. Common industrial adaptations of this ability include diamond-tipped drill bits and saws, and the use of diamond powder as an abrasive. Less expensive industrial-grade diamonds, known as bort, with more flaws and poorer color than gems, are used for such purposes.
Diamond is not suitable for machining ferrous alloys at high speeds as carbon is soluble in iron at the high temperatures created by high-speed machining, leading to greatly increased wear on diamond tools when compared to alternatives.
These substances can scratch diamond:
Some diamonds are harder than others.
boron nitride
Borazon - a boron nitride allotrope
Rhenium diboride
Hexagonal form of diamond called lonsdaleite, is theoretically predicted to be 58% stronger than diamond. [13]
Aggregated diamond nanorods, a material produced by high-pressure high-temperature treatment of fullerite (C60).
Electrical conductivity
Other specialized applications also exist or are being developed, including use as semiconductors: some blue diamonds are natural semiconductors, in contrast to most other diamonds, which are excellent electrical insulators.[11] The conductivity and blue color originate from the boron impurity. Boron substitutes for carbon atoms in the diamond lattice, donating a hole into the valence band.
Substantial conductivity is commonly observed in nominally undoped diamond grown by chemical vapor deposition.[14] This conductivity is associated with hydrogen-related species adsorbed at the surface, and it can be removed by annealing or other surface treatments.
Toughness
Toughness relates to a material's ability to resist breakage from forceful impact. The toughness of natural diamond has been measured as 3.4 MN m-3/2,[15] which is good compared to other gemstones, but poor compared to most engineering materials. As with any material, the macroscopic geometry of a diamond contributes to its resistance to breakage. Diamond has a cleavage plane and is therefore more fragile in some orientations than others. Diamond cutters use this attribute to cleave some stones, prior to faceting.
Color
Main article: Diamond color
Brown colored dia
monds at the National Museum of Natural History
Gem quality diamond may be colorless or occur in any hue including the non-spectral hues of gray, brown and black. Diamond is the only gemstone composed of a single element, carbon. The diamond crystal lattice is exceptionally strong and only atoms of nitrogen, boron, hydrogen, phosphorus and maybe beryllium can be introduced into diamond during the growth at significant concentrations. Transition metals Ni and Co, which are commonly used for growth of synthetic diamond by the high-pressure high-temperature techniques, have been detected in diamond as individual atoms, however the maximum concentration is 0.01% for Ni[16] and even much less for Co. Note however, that virtually any element can be introduced in diamond by ion implantation.
Nitrogen is the smallest and by far the most common impurity found in gem diamonds. Nitrogen is responsible for the yellow and brown in diamonds. Boron is responsible for the gray blue colors. Color in diamond has two additional sources: irradiation (usually by alpha particles), that causes the color in green diamonds; and physical deformation of the diamond crystal known as plastic deformation. Plastic deformation is the cause of color in some brown[17] and perhaps pink and red diamonds.[18] In order of rarity, colorless diamond, by far the most common, is followed by yellow and brown, by far the most common colors, then by blue, green, black, translucent white, pink, violet, orange, purple, and the rarest, red.[11] "Black," or Carbonado, diamonds are not truly black, but rather contain numerous dark inclusions that give the gems their dark appearance. Colored diamonds contain impurities or structural defects that cause the coloration, while pure or nearly pure diamonds are transparent and colorless. Most diamond impurities replace a carbon atom in the crystal lattice, known as a carbon flaw. The most common impurity, nitrogen, causes a slight to intense yellow coloration depending upon the type and concentration of nitrogen present.[11] The Gemological Institute of America (GIA) classifies low saturation yellow and brown diamonds as diamonds in the normal color range, and applies a grading scale from 'D' (colorless) to 'Z' (light yellow). Diamonds of a different color, such as blue, are called fancy colored diamonds, and fall under a different grading scale.
In 2008, the Wittelsbach Diamond, a 35.56 carats (7.11 g) blue diamond once belonging to the King of Spain, fetched over $24M US at a Christie's auction. The blue hue was a result of trace amounts of boron in the stone's crystal structure.[19]
Identification
Diamonds can be identified by their high thermal conductivity. Their high refractive index is also indicative, but other materials have similar refractivity. Diamonds do cut glass, but other materials, such as quartz, also lie above glass on Mohs scale. Diamonds easily scratch other diamonds, but this damages both diamonds.
Natural history
The formation of natural diamond requires very specific conditions. Diamond formation requires exposure of carbon-bearing materials to high pressure, ranging approximately between 45 and 60 kilobars,[20] but at a comparatively low temperature range between approximately 1650–2370 °F (900–1300 °C).[20] These conditions are known to be met in two places on Earth; in the lithospheric mantle below relatively stable continental plates, and at the site of a meteorite strike.
Formation in cratons
The conditions for diamond formation to happen in the lithospheric mantle occur at considerable depth corresponding to the aforementioned requirements of temperature and pressure. These depths are estimated to be in between 140–190 kilometers (90–120 miles)[20][11] though occasionally diamonds have crystallized at depths of 300-400
km (180-250 miles) as well.[21] The rate at which temperature changes with increasing depth into the Earth varies greatly in different parts of the Earth. In particular, under oceanic plates the temperature rises more quickly with depth, beyond the range required for diamond formation at the depth required.[20] The correct combination of temperature and pressure is only found in the thick, ancient, and stable parts of continental plates where regions of lithosphere known as cratons exist.[20] Long residence in the cratonic lithosphere allows diamond crystals to grow larger.
The slightly misshapen octahedral shape of this rough diamond crystal in matrix is typical of the mineral. Its lustrous faces also indicate that this crystal is from a primary deposit.
Through studies of carbon isotope ratios (similar to the methodology used in carbon dating, except with the stable isotopes C-12 and C-13), it has been shown that the carbon found in diamonds comes from both inorganic and organic sources. Some diamonds, known as harzburgitic, are formed from inorganic carbon originally found deep in the Earth's mantle. In contrast, eclogitic diamonds contain organic carbon from organic detritus that has been pushed down from the surface of the Earth's crust through subduction (see plate tectonics) before transforming into diamond.[11] These two different source carbons have measurably different 13C:12C ratios. Diamonds that have come to the Earth's surface are generally quite old, ranging from under 1 billion to 3.3 billion years old. This is 22% to 73% of the age of the Earth.
Diamonds occur most often as euhedral or rounded octahedra and twinned octahedra known as macles or maccles. As diamond's crystal structure has a cubic arrangement of the atoms, they have many facets that belong to a cube, octahedron, rhombicosidodecahedron, tetrakis hexahedron or disdyakis dodecahedron. The crystals can have rounded off and unexpressive edges and can be elongated. Sometimes they are found grown together or form double "twinned" crystals at the surfaces of the octahedron. These different shapes and habits of the diamonds result from differing external circumstances. Diamonds (especially those with rounded crystal faces) are commonly found coated in nyf, an opaque gum-like skin.[22]
Formation in meteorite impact craters
Diamonds can also form in other natural high-pressure events. Very small diamonds, known as microdiamonds or nanodiamonds, have been found in meteorite impact craters. Such impact events create shock zones of high pressure and temperature suitable for diamond formation. Impact-type microdiamonds can be used as one indicator of ancient impact craters.[11]
Extraterrestrial formation
Not all diamonds found on earth originated here. A type of diamond called carbonado diamond that is found in South America and Africa may have been deposited there via an asteroid impact (not formed from the impact) about 3 billion years ago.[23][24] These diamonds may have formed in the intrastellar environment, but as of 2008, there was no scientific consensus on how carbonado diamonds originated.
Presolar grains in many meteorites found on earth contain nanodiamonds of extraterrestrial origin, probably formed in supernovas.
Scientific evidence indicates that white dwarf stars have a core of crystallized carbon and oxygen nuclei. The largest of these found in the universe so far, BPM 37093, is located 50 light years away in the constellation Centaurus. A news release from the Harvard-Smithsonian Center for Astrophysics described the 2,500 mile-wide stellar core as a diamond.[25] It is estimated to be ten billion trillion trillion carats, more or less. It was referred to as Lucy, after the Beatles song "Lucy in the Sky With Diamonds".[26][2]
Surfacing
Schematic diagram of a volcanic pipe
Diamond-bearing rock is brought close to the surface through deep-origin volcanic eruptions. The magma for such a volcano must originate at a depth where diamonds can be formed[11] — 150 km (90 miles) or more (three times or more the depth of source magma for most volcanoes). This is a relatively rare occurrence. These typically small surface volcanic craters extend downward in formations known as volcanic pipes.[11] The pipes contain material that was transported toward the surface by volcanic action, but was not ejected before the volcanic activity ceased. During eruption these pipes are open to the surface, resulting in open circulation; many xenoliths of surface rock and even wood and/or fossils are found in volcanic pipes. Diamond-bearing volcanic pipes are closely related to the oldest, coolest regions of continental crust (cratons). This is because cratons are very thick, and their lithospheric mantle extends to great enough depth that diamonds are stable. Not all pipes contain diamonds, and even fewer contain enough diamonds to make mining economically viable.
The magma in volcanic pipes is usually one of two characteristic types, which cool into igneous rock known as either kimberlite or lamproite.[11] The magma itself does not contain diamond; instead, it acts as an elevator that carries deep-formed rocks (xenoliths), minerals (xenocrysts), and fluids upward. These rocks are characteristically rich in magnesium-bearing olivine, pyroxene, and amphibole minerals[11] which are often altered to serpentine by heat and fluids during and after eruption. Certain indicator minerals typically occur within diamondiferous kimberlites and are used as mineralogic tracers by prospectors, who follow the indicator trail back to the volcanic pipe which may contain diamonds. These minerals are rich in chromium (Cr) or titanium (Ti), elements which impart bright colors to the minerals. The most common indicator minerals are chromian garnets (usually bright red Cr-pyrope, and occasionally green ugrandite-series garnets), eclogitic garnets, orange Ti-pyrope, red high-Cr spinels, dark chromite, bright green Cr-diopside, glassy green olivine, black picroilmenite, and magnetite.[11] Kimberlite deposits are known as blue ground for the deeper serpentinized part of the deposits, or as yellow ground for the near surface smectite clay and carbonate weathered and oxidized portion.
Once diamonds have been transported to the surface by magma in a volcanic pipe, they may erode out and be distributed over a large area. A volcanic pipe containing diamonds is known as a primary source of diamonds. Secondary sources of diamonds include all areas where a significant number of diamonds, eroded out of their kimberlite or lamproite matrix, and accumulated because of water or wind action. These include alluvial deposits and deposits along existing and ancient shorelines, where loose diamonds tend to accumulate because of their approximate size and density. Diamonds have also rarely been found in deposits left behind by glaciers (notably in Wisconsin and Indiana); however, in contrast to alluvial deposits, glacial deposits are not known to be of significant concentration and are therefore not viable commercial sources of diamond.
Commercial markets
A round brilliant cut diamond set in a ring
The diamond indust
ry can be broadly separated into two basically distinct categories: one dealing with gem-grade diamonds and another for industrial-grade diamonds. While a large trade in both types of diamonds exists, the two markets act in dramatically different ways.
Gemstones
Main article: Diamond (gemstone)
A large trade in gem-grade diamonds exists. Unlike precious metals such as gold or platinum, gem diamonds do not trade as a commodity: there is a substantial mark-up in the retail sale of diamonds. Contrary to popular belief, there is a well-established market for resale of polished diamonds (e.g. pawnbroking, auctions, second-hand jewellery stores, diamantaires, bourses, etc.). One hallmark of the trade in gem-quality diamonds is its remarkable concentration: wholesale trade and diamond cutting is limited to just a few locations. 92% of diamond pieces cut in 2003 were in Surat, Gujarat, India.[27] Other important centers of diamond cutting and trading are Antwerp, where the International Gemological Institute is based, London, New York, Tel Aviv, and Amsterdam. A single company—De Beers—controls a significant proportion of the trade in diamonds. They are based in Johannesburg, South Africa and London, England. One contributory factor is the geological nature of diamond deposits: several large primary kimberlite-pipe mines each account for significant portions of market share (such as the Jwaneng mine in Botswana, which is a single large pit operated by De Beers that can produce between 12.5 to 15 million carats of diamonds per year[28]), whereas secondary alluvial diamond deposits tend to be fragmented amongst many different operators because they can be dispersed over many hundreds of square kilometres (e.g. alluvial deposits in Brazil).
The production and distribution of diamonds is largely consolidated in the hands of a few key players, and concentrated in traditional diamond trading centers. The most important being Antwerp, where 80% of all rough diamonds, 50% of all cut diamonds and more than 50% of all rough, cut and industrial diamonds combined are handled.[citation needed] This makes Antwerp the de facto 'world diamond capital'. New York, however, along with the rest of the United States, is where almost 80% of the world's diamonds are sold, including auction sales. Also, the largest and most unusually shaped rough diamonds end up in New York.[citation needed] The De Beers company, as the world's largest diamond miner holds a clearly dominant position in the industry, and has done so since soon after its founding in 1888 by the British imperialist Cecil Rhodes. De Beers owns or controls a significant portion of the world's rough diamond production facilities (mines) and distribution channels for gem-quality diamonds. The company and its subsidiaries own mines that produce some 40 percent of annual world diamond production. At one time it was thought over 80 percent of the world's rough diamonds passed through the Diamond Trading Company (DTC, a subsidiary of De Beers) in London[1], but presently the figure is estimated at around 40 percent[2]. De Beers sold off the vast majority its diamond stockpile in the late 1990s - early 2000s[3] and the remainder largely represents working stock (diamonds that are being sorted before sale)[4]. This was well-documented in the press[5] but remains little-known to the general public.
The De Beers diamond advertising campaign is acknowledged as one of the most successful and innovative campaigns in history. N. W. Ayer & Son, the advertising firm retained by De Beers in the mid-20th century, succeeded in reviving the American diamond market and opened up new markets, even in countries where no diamond tradition had existed before. N.W. Ayer's multifaceted marketing campaign included product placement, advertising the diamond itself rather than the De Beers brand, and building associations with celebrities and royalty. This coordinated campaign has lasted decades and continues today; it is perhaps best captured by the slogan "a diamond is forever".
Further down the supply chain, members of The World Federation of Diamond Bourses (WFDB) act as a medium for wholesale diamond exchange, trading both polished and rough diamonds. The WFDB consists of independent diamond bourses in major cutting centres such as Tel Aviv, Antwerp, Johannesburg and other cities across the USA, Europe and Asia.
In 2000, the WFDB and The International Diamond Manufacturers Association established the World Diamond Council to prevent the trading of diamonds used to fund war and inhumane acts.
WFDB's additional activities also include sponsoring the World Diamond Congress every two years, as well as the establishment of the International Diamond Council (IDC) to oversee diamond grading.
Industrial grade
Diamonds in an angle grinder blade
The market for industrial-grade diamonds operates much differently from its gem-grade counterpart. Industrial diamonds are valued mostly for their hardness and heat conductivity, making many of the gemological characteristics of diamonds, such as clarity and color, irrelevant for most applications. This helps explain why 80% of mined diamonds (equal to about 100 million carats or 20,000 kg annually), unsuitable for use as gemstones, are destined for industrial use. In addition to mined diamonds, synthetic diamonds found industrial applications almost immediately after their invention in the 1950s; another 3 billion carats (600 metric tons)[citation needed] of synthetic diamond is produced annually for industrial use. Approximately 90% of diamond grinding grit is currently of synthetic origin.
The dominant industrial use of diamond is in cutting, drilling, grinding, and polishing. Most uses of diamonds in these technologies do not require large diamonds; in fact, most diamonds that are gem-quality except for their small size, can find an industrial use. Diamonds are embedded in drill tips or saw blades, or ground into a powder for use in grinding and polishing applications. Specialized applications include use in laboratories as containment for high pressure experiments (see diamond anvil cell), high-performance bearings, and limited use in specialized windows.
With the continuing advances being made in the production of synthetic diamonds, future applications are beginning to become feasible. Garnering much excitement is the possible use of diamond as a semiconductor suitable to build microchips from, or the use of diamond as a heat sink in electronics.
The boundary between gem-quality diamonds and industrial diamonds is poorly-defined and partly depends on market conditions (for example, if demand for polished diamonds is high, some suitable stones will be polished into low-quality or small gemstones rather than being sold for industrial use). Within the category of industrial diamonds, there is a sub-category comprising the lowest-quality, mostly opaque stones, which are known as bort or 'boart'.
Supply chain
Diamond output in 2005
See also: List of diamond mines
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 can bring diamond crystals, originating from deep within the Earth where high pressures and temperatures enable them to form, to the surface. The mining and distribution of natural diamonds are subjects of frequent controversy such as with concerns over the sale of conflict diamonds (aka blood diamonds) by African paramilitary groups.
The diamond supply chain is controlled by a limited number of powerful businesses, and is also highly concentrated in a small number of locations around the world.
Mining, sources and production
Only a very small fraction of the diamond ore consists of actual diamonds. The ore is crushed, during which care has to be taken in order to prevent larger diamonds from being destroyed, and then sorted by density. Today, diamonds are located in the diamond-rich density fraction with the help of X-ray fluorescence, after which the final sorting steps are done by hand. Before the use of X-rays became commonplace, the separation was done with grease belts; diamonds have a stronger tendency to stick to grease than the other minerals in the ore.
Historically diamonds were known to be found only in alluvial deposits in southern India.[29] India led the world in diamond production from the time of their discovery in approximately the 9th century BCE[30][6] to the mid-18th century AD, but the commercial potential of these sources had been exhausted by the late 18th century and at that time India was eclipsed by Brazil where the first non-Indian diamonds were found in 1725.[6]
Diamond production of primary deposits (kimberlites and lamproites) only started in the 1870s after the discovery of the Diamond fields in South Africa. Production has increased over time and now an accumulated total of 4.5 billion carats have been mined since that date.[31] Interestingly 20% of that amount has been mined in the last 5 years alone and during the last ten years 9 new mines have started production while 4 more are waiting to be opened soon. Most of these mines are located in Canada, Zimbabwe, Angola, and one in Russia.[31]
In the U.S., diamonds have been found in Arkansas, Colorado, and Montana.[32][33] In 2004, a startling discovery of a microscopic diamond in the U.S.[34] led to the January 2008 bulk-sampling of kimberlite pipes in a remote part of Montana.[35]
Today, most commercially viable diamond deposits are in Russia (mostly in Yakutia, for example Mir pipe and Udachnaya pipe), Botswana, Australia (Northern and Western Australia) and the Democratic Republic of Congo.[36]
In 2005, Russia produced almost one-fifth of the global diamond output, reports the British Geological Survey. Australia boasts the richest diamondiferous pipe with production reaching peak levels of 42 metric tons (41 LT; 46 ST) per year in the 1990s.[32]
There are also commercial deposits being actively mined in the Northwest Territories of Canada and Brazil. Diamond prospectors continue to search the globe for diamond-bearing kimberlite and lamproite pipes.
Controversial sources
Main article: Blood diamond
In some of the more politically unstable central African and west African countries, revolutionary groups have taken control of diamond mines, using proceeds from diamond sales to finance their operations. Diamonds sold through this process are known as conflict diamonds or blood diamonds. Major diamond trading corporations continue to fund and fuel these conflicts by doing business with armed groups. In response to public concerns that their diamond purchases were contributing to war and human rights abuses in central and western Africa, the United Nations, the diamond industry and diamond-trading nations introduced the Kimberley Process in 2002. The Kimberley Process aims to ensure that conflict diamonds do not become intermixed with the diamonds not controlled by such rebel groups. This is done by requiring diamond-producing countries to provide proof that the money they make from selling the diamonds is not used to fund criminal or revolutionary activities. Although the Kimberley Process has been moderately successful in limiting the number of conflict diamonds entering the market, some still find their way in. 2–3% of all diamonds traded today are potentially conflict diamonds[37]. Two major flaws still hinder the effectiveness of the Kimberley Process: (1) the relative ease of smuggling diamonds across African borders, and (2) the violent nature of diamond mining in nations that are not in a technical state of war and whose diamonds are therefore considered "clean."[38]
The Canadian Government has set up a body known as Canadian Diamond Code of Conduct[39] to help authenticate Canadian diamonds. This is a very stringent tracking system of diamonds and helps protect the 'conflict free' label of Canadian diamonds.
Distribution
The Diamond Trading Company (DTC) is a subsidiary of De Beers and markets rough diamonds from De Beers-operated mines (it withdrew from purchasing diamonds on the open market in 1999 and ceased purchasing Russian diamonds mined by Russian company Alrosa, at the end of 2008 and, although Alrosa has successfully appealed against a European court ruling[6], according to a statement by an Alrosa spokesperson, sales do not appear to have resumed[7]).
Once purchased by Sightholders (which is a trademark term referring to the companies that have a three-year supply contract with DTC), diamonds are cut and polished in preparation for sale as gemstones. The cutting and polishing of rough diamonds is a specialized skill that is concentrated in a limited number of locations worldwide. Traditional diamond cutting centers are Antwerp, Amsterdam, Johannesburg, New York, and Tel Aviv. Recently, diamond cutting centers have been established in China, India, Thailand, Namibia and Botswana. Cutting centers with lower cost of labor, notably Surat in Gujarat, India, handle a larger number of smaller carat diamonds, while smaller quantities of larger or more valuable diamonds are more likely to be handled in Europe or North America. The recent expansion of this industry in India, employing low cost labor, has allowed smaller diamonds to be prepared as gems in greater quantities than was previously economically feasible.
Diamonds which have been prepared as gemstones are sold on diamond exchanges called bourses. There are 26 registered diamond bourses in the world.[40] Bourses are the final tightly controlled step in the diamond supply chain; wholesalers and even retailers are able to buy relatively small lots of diamonds at the bourses, after which they are prepared for final sale to the consumer. Diamonds can be sold already set in jewelry, or sold unset ("loose"). According to the Rio Tinto Group, in 2002 the diamonds produced and released to the market were valued at US$9 billion as rough diamonds, US$14 billion after being cut and polished, US$28 billion in wholesale diamond jewelry, and US$57 billion in retail sales.
Synthetics, simulants, and enhancements
Main articles: Synthetic diamond, Diamond simulant, and Diamond enhancement
Synthetics
Synthetic diamonds are diamond crystals that are manufactured in a laboratory, as opposed to natural diamonds which form naturally within the earth.
The gemological and industrial uses of diamond have created a large demand for rough stones. This demand has long been satisfied in large part by synthetic diamonds, which have been manufactured by various processes for more than half a century. However, in recent years it has become possible to produce gem-quality synthetic diamonds of significant size.[41]
The majority of commercially available synthetic diamonds are yellow in color and produced by so called High Pressure High Temperature (HPHT) processes.[42] The yellow color is caused by nitrogen impurities. Other colors may also be reproduced such as blue, green or pink which are a result of the addition of boron or from irradiation after synthesis.[43]
At present, the annual production of gem quality synthetic diamonds is only a few thousand carats, whereas the total production of natural diamonds is around 120 million carats. Despite this fact, a purchaser is more likely to encounter a synthetic when looking for a fancy-colored diamond because nearly all synthetic diamonds are fancy-colored, while only 0.01% of natural diamonds are fancy-colored.[44]
Producing large synthetic diamonds threatens the business model of the diamond industry. The ultimate effect of the ready availability of gem-quality diamonds at low cost in the future is hard to predict.
Simulants
A diamond simulant is defined as a non-diamond material that is used to simulate the appearance of a diamond. Diamond-simulant gems are often referred to as diamante.
The most familiar diamond simulant to most consumers is cubic zirconia (commonly abbreviated as CZ). The popular gemstone moissanite is often mischaracterized as a diamond simulant, although it is marketed as a gemstone in its own right rather than explicitly as a diamond simulant. While moissanite does look similar to diamond, its main disadvantage as a diamond simulant is that CZ is far cheaper and arguably equally convincing. Both CZ and moissanite are synthetically produced.
Enhancements
Diamond enhancements are specific treatments performed on natural or synthetic diamonds (usually those already cut and polished into a gem), which are designed to better the gemological characteristics of the stone in one or more ways. These include laser drilling to remove inclusions, application of sealants to fill cracks, treatments to improve a white diamond's color grade, and treatments to give fancy color to a white diamond.
Coatings are increasingly used to give a diamond simulant such as cubic zirconia a more "diamond-like" appearance. One such substance, which is heavily advertised, is what scientists refer to as "diamond-like carbon". This is an amorphous carbonaceous material that has some physical properties which are similar to that of the diamond. Advertising suggests that such a coating would transfer some of these diamond-like properties to the coated stone, hence enhancing the diamond simulant. However, modern techniques such as Raman Spectroscopy should easily identify such as treatment.[45]
Identification
In the 22 November 2008 issue of New Scientist, it was stated that Russell Hemley of the Geophysical Laboratory at the Carnegie Institution for Science had discovered a technique to make diamonds via microwaves which were indistiguishable from natural diamonds. Yufei Meng, a scientist from the same laboratory, claimed that after having sent these diamonds for diamond jewellery identification, they were not identified as different from natural diamonds.[citation needed] Such claims are often made for new synthetics, simulants, and treated stones, so it is important to validate how the stones were submitted for identification. For example, the "test" could simply refer to showing the stones to an unqualified jewellery shop assistant.
Properly-trained and equipped gemologists can distinguish between natural diamonds and synthetic diamonds. They can also identify the vast majority of treated natural diamonds, two exceptions being a small minority of HPHT-treated Type II diamonds and some artificially-irradiated green diamonds. "Perfect" crystals (at the atomic lattice level) have never been found to exist anywhere, so both natural and synthetic diamonds always possess characteristic imperfections, arising from the circumstances of their crystal growth, that allow them to be distinguished from each other.
Laboratories use techniques such as spectroscopy, microscopy and luminescence under shortwave ultraviolet light to determine a diamond's origin. They also use specially-made machines to aid them in the identification process. Two screening machines are the DiamondSure and the DiamondView, both produced by the DTC and marketed by the GIA.[46]
Several methods for identifying synthetic diamonds can be performed, depending on the method of production and the color of the diamond. CVD diamonds can usually be identified by an orange fluorescence. D-J colored diamonds can be screened through the Swiss Gemological Organization's[47] Diamond Spotter. Stones in the D-Z color range can be examined through the DiamondSure UV/visible spectrometer which is a tool developed by De Beers.[48] Similarly, natural diamonds usually have minor imperfections and flaws, such as inclusions of foreign material, that are not seen in synthetic diamonds
of carbon where the carbon atoms are arranged in an isometric-hexoctahedral crystal lattice. After graphite, diamond is the second most stable form of carbon. Its hardness and high dispersion of light make it useful for industrial applications and jewelry. It is the hardest known naturally occurring mineral. It is possible to treat regular diamonds under a combination of high pressure and high temperature to produce diamonds that are harder than the diamonds used in hardness gauges.[2]Diamonds are specifically renowned as a material with superlative physical qualities; they make excellent abrasives because few substances can scratch them. As a result they hold a polish extremely well and retain their lustre. Approximately 130 million carats (26,000 kg (57,000 lb)) are mined annually, with a total value of nearly USD $9 billion, and about 100,000 kg (220,000 lb) are synthesized annually.[3]
History
See also: Diamond (gemstone)
Diamonds have been treasured as gemstones since their use as religious icons in ancient India. Their usage in engraving tools also dates to early human history.[4][5] 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.
Diamonds are thought to have been first recognized and mined in India, where significant alluvial deposits of the stone could then be found many centuries ago along the rivers Penner, Krishna and Godavari. Diamonds have been known in India for at least 3000 years but most likely 6000 years.[6]
The name diamond is derived from the ancient Greek ἀδάμας (adámas), "unbreakable, untamed", from ἀ- (a-), "un-" + δαμάω (damáō), "I overpower, I tame"[7], and is the real-world origin of myths about a superhard metal called adamant.
In 1813, Humphry Davy used a lens to concentrate the rays of the sun on a diamond in an atmosphere of oxygen, and showed that the only product of the combustion was carbon dioxide, proving that diamond is composed of carbon.[8] Later, he showed that in an atmosphere devoid of oxygen, diamond is converted to graphite.
The most familiar usage of diamonds today is as gemstones used for adornment, a usage which dates back into antiquity. The dispersion of white light into spectral colors, is the primary gemological characteristic of gem diamonds.
In the twentieth century, experts in the field of gemology have developed methods of grading diamonds and other gemstones based on the characteristics most important to their value as a gem. Four characteristics, known informally as the four Cs, are now commonly used as the basic descriptors of diamonds: these are carat, cut, color, and clarity.
Material properties
Main article: Material properties of diamond
Diamond and g
raphite are two allotropes of carbon: pure forms of the same element that differ in structure.A diamond is a transparent crystal of tetrahedrally bonded carbon atoms (sp3) that crystallizes into the face centered cubic diamond lattice structure. Diamonds have been adapted for many uses because of the material's exceptional physical characteristics. Most notable are its extreme hardness, its high dispersion index, and extremely high thermal conductivity (900 – 2320 W/m K). Above 1700 °C (1973 K / 3583 °F), diamond is converted to graphite.[9] Naturally occurring diamonds have a density ranging from 3.15 to 3.53 g/cm³, with very pure diamond typically extremely close to 3.52 g/cm³.
Hardness
Diamond is the hardest natural material known, where hardness is defined as resistance to scratching.[10] Diamond has a hardness of 10 (hardest) on Mohs scale of mineral hardness.[11] Diamond's hardness has been known since antiquity, and is the source of its name.
The hardest diamonds in the world are from the Copeton and Bingara fields located in the New England area in New South Wales, Australia. They were called can-ni-fare (cannot be cut) by the cutters in Antwerp when they started to arrive in quantity from Australia in the 1870s. These diamonds are generally small, perfect to semiperfect octahedra, and are used to polish other diamonds. Their hardness is considered to be a product of the crystal growth form, which is single stage growth crystal. Most other diamonds show more evidence of multiple growth stages, which produce inclusions, flaws, and defect planes in the crystal lattice, all of which affect their hardness.[12]
The hardness of diamonds contributes to its suitability as a gemstone. Because it can only be scratched by other diamonds, it maintains its polish extremely well. Unlike many other gems, it is well-suited to daily wear because of its resistance to scratching—perhaps contributing to its popularity as the preferred gem in engagement or wedding rings, which are often worn every day.
Industrial use of diamonds has historically been associated with their hardness; this property makes diamond the ideal material for cutting and grinding tools. As the hardest known naturally-occurring material, diamond can be used to polish, cut, or wear away any material, including other diamonds. Common industrial adaptations of this ability include diamond-tipped drill bits and saws, and the use of diamond powder as an abrasive. Less expensive industrial-grade diamonds, known as bort, with more flaws and poorer color than gems, are used for such purposes.
Diamond is not suitable for machining ferrous alloys at high speeds as carbon is soluble in iron at the high temperatures created by high-speed machining, leading to greatly increased wear on diamond tools when compared to alternatives.
These substances can scratch diamond:
Some diamonds are harder than others.
boron nitride
Borazon - a boron nitride allotrope
Rhenium diboride
Hexagonal form of diamond called lonsdaleite, is theoretically predicted to be 58% stronger than diamond. [13]
Aggregated diamond nanorods, a material produced by high-pressure high-temperature treatment of fullerite (C60).
Electrical conductivity
Other specialized applications also exist or are being developed, including use as semiconductors: some blue diamonds are natural semiconductors, in contrast to most other diamonds, which are excellent electrical insulators.[11] The conductivity and blue color originate from the boron impurity. Boron substitutes for carbon atoms in the diamond lattice, donating a hole into the valence band.
Substantial conductivity is commonly observed in nominally undoped diamond grown by chemical vapor deposition.[14] This conductivity is associated with hydrogen-related species adsorbed at the surface, and it can be removed by annealing or other surface treatments.
Toughness
Toughness relates to a material's ability to resist breakage from forceful impact. The toughness of natural diamond has been measured as 3.4 MN m-3/2,[15] which is good compared to other gemstones, but poor compared to most engineering materials. As with any material, the macroscopic geometry of a diamond contributes to its resistance to breakage. Diamond has a cleavage plane and is therefore more fragile in some orientations than others. Diamond cutters use this attribute to cleave some stones, prior to faceting.
Color
Main article: Diamond color
Brown colored dia
monds at the National Museum of Natural HistoryGem quality diamond may be colorless or occur in any hue including the non-spectral hues of gray, brown and black. Diamond is the only gemstone composed of a single element, carbon. The diamond crystal lattice is exceptionally strong and only atoms of nitrogen, boron, hydrogen, phosphorus and maybe beryllium can be introduced into diamond during the growth at significant concentrations. Transition metals Ni and Co, which are commonly used for growth of synthetic diamond by the high-pressure high-temperature techniques, have been detected in diamond as individual atoms, however the maximum concentration is 0.01% for Ni[16] and even much less for Co. Note however, that virtually any element can be introduced in diamond by ion implantation.
Nitrogen is the smallest and by far the most common impurity found in gem diamonds. Nitrogen is responsible for the yellow and brown in diamonds. Boron is responsible for the gray blue colors. Color in diamond has two additional sources: irradiation (usually by alpha particles), that causes the color in green diamonds; and physical deformation of the diamond crystal known as plastic deformation. Plastic deformation is the cause of color in some brown[17] and perhaps pink and red diamonds.[18] In order of rarity, colorless diamond, by far the most common, is followed by yellow and brown, by far the most common colors, then by blue, green, black, translucent white, pink, violet, orange, purple, and the rarest, red.[11] "Black," or Carbonado, diamonds are not truly black, but rather contain numerous dark inclusions that give the gems their dark appearance. Colored diamonds contain impurities or structural defects that cause the coloration, while pure or nearly pure diamonds are transparent and colorless. Most diamond impurities replace a carbon atom in the crystal lattice, known as a carbon flaw. The most common impurity, nitrogen, causes a slight to intense yellow coloration depending upon the type and concentration of nitrogen present.[11] The Gemological Institute of America (GIA) classifies low saturation yellow and brown diamonds as diamonds in the normal color range, and applies a grading scale from 'D' (colorless) to 'Z' (light yellow). Diamonds of a different color, such as blue, are called fancy colored diamonds, and fall under a different grading scale.
In 2008, the Wittelsbach Diamond, a 35.56 carats (7.11 g) blue diamond once belonging to the King of Spain, fetched over $24M US at a Christie's auction. The blue hue was a result of trace amounts of boron in the stone's crystal structure.[19]
Identification
Diamonds can be identified by their high thermal conductivity. Their high refractive index is also indicative, but other materials have similar refractivity. Diamonds do cut glass, but other materials, such as quartz, also lie above glass on Mohs scale. Diamonds easily scratch other diamonds, but this damages both diamonds.
Natural history
The formation of natural diamond requires very specific conditions. Diamond formation requires exposure of carbon-bearing materials to high pressure, ranging approximately between 45 and 60 kilobars,[20] but at a comparatively low temperature range between approximately 1650–2370 °F (900–1300 °C).[20] These conditions are known to be met in two places on Earth; in the lithospheric mantle below relatively stable continental plates, and at the site of a meteorite strike.
Formation in cratons
The conditions for diamond formation to happen in the lithospheric mantle occur at considerable depth corresponding to the aforementioned requirements of temperature and pressure. These depths are estimated to be in between 140–190 kilometers (90–120 miles)[20][11] though occasionally diamonds have crystallized at depths of 300-400
km (180-250 miles) as well.[21] The rate at which temperature changes with increasing depth into the Earth varies greatly in different parts of the Earth. In particular, under oceanic plates the temperature rises more quickly with depth, beyond the range required for diamond formation at the depth required.[20] The correct combination of temperature and pressure is only found in the thick, ancient, and stable parts of continental plates where regions of lithosphere known as cratons exist.[20] Long residence in the cratonic lithosphere allows diamond crystals to grow larger.The slightly misshapen octahedral shape of this rough diamond crystal in matrix is typical of the mineral. Its lustrous faces also indicate that this crystal is from a primary deposit.
Through studies of carbon isotope ratios (similar to the methodology used in carbon dating, except with the stable isotopes C-12 and C-13), it has been shown that the carbon found in diamonds comes from both inorganic and organic sources. Some diamonds, known as harzburgitic, are formed from inorganic carbon originally found deep in the Earth's mantle. In contrast, eclogitic diamonds contain organic carbon from organic detritus that has been pushed down from the surface of the Earth's crust through subduction (see plate tectonics) before transforming into diamond.[11] These two different source carbons have measurably different 13C:12C ratios. Diamonds that have come to the Earth's surface are generally quite old, ranging from under 1 billion to 3.3 billion years old. This is 22% to 73% of the age of the Earth.
Diamonds occur most often as euhedral or rounded octahedra and twinned octahedra known as macles or maccles. As diamond's crystal structure has a cubic arrangement of the atoms, they have many facets that belong to a cube, octahedron, rhombicosidodecahedron, tetrakis hexahedron or disdyakis dodecahedron. The crystals can have rounded off and unexpressive edges and can be elongated. Sometimes they are found grown together or form double "twinned" crystals at the surfaces of the octahedron. These different shapes and habits of the diamonds result from differing external circumstances. Diamonds (especially those with rounded crystal faces) are commonly found coated in nyf, an opaque gum-like skin.[22]
Formation in meteorite impact craters
Diamonds can also form in other natural high-pressure events. Very small diamonds, known as microdiamonds or nanodiamonds, have been found in meteorite impact craters. Such impact events create shock zones of high pressure and temperature suitable for diamond formation. Impact-type microdiamonds can be used as one indicator of ancient impact craters.[11]
Extraterrestrial formation
Not all diamonds found on earth originated here. A type of diamond called carbonado diamond that is found in South America and Africa may have been deposited there via an asteroid impact (not formed from the impact) about 3 billion years ago.[23][24] These diamonds may have formed in the intrastellar environment, but as of 2008, there was no scientific consensus on how carbonado diamonds originated.
Presolar grains in many meteorites found on earth contain nanodiamonds of extraterrestrial origin, probably formed in supernovas.
Scientific evidence indicates that white dwarf stars have a core of crystallized carbon and oxygen nuclei. The largest of these found in the universe so far, BPM 37093, is located 50 light years away in the constellation Centaurus. A news release from the Harvard-Smithsonian Center for Astrophysics described the 2,500 mile-wide stellar core as a diamond.[25] It is estimated to be ten billion trillion trillion carats, more or less. It was referred to as Lucy, after the Beatles song "Lucy in the Sky With Diamonds".[26][2]
Surfacing
Schematic diagram of a volcanic pipe
Diamond-bearing rock is brought close to the surface through deep-origin volcanic eruptions. The magma for such a volcano must originate at a depth where diamonds can be formed[11] — 150 km (90 miles) or more (three times or more the depth of source magma for most volcanoes). This is a relatively rare occurrence. These typically small surface volcanic craters extend downward in formations known as volcanic pipes.[11] The pipes contain material that was transported toward the surface by volcanic action, but was not ejected before the volcanic activity ceased. During eruption these pipes are open to the surface, resulting in open circulation; many xenoliths of surface rock and even wood and/or fossils are found in volcanic pipes. Diamond-bearing volcanic pipes are closely related to the oldest, coolest regions of continental crust (cratons). This is because cratons are very thick, and their lithospheric mantle extends to great enough depth that diamonds are stable. Not all pipes contain diamonds, and even fewer contain enough diamonds to make mining economically viable.
The magma in volcanic pipes is usually one of two characteristic types, which cool into igneous rock known as either kimberlite or lamproite.[11] The magma itself does not contain diamond; instead, it acts as an elevator that carries deep-formed rocks (xenoliths), minerals (xenocrysts), and fluids upward. These rocks are characteristically rich in magnesium-bearing olivine, pyroxene, and amphibole minerals[11] which are often altered to serpentine by heat and fluids during and after eruption. Certain indicator minerals typically occur within diamondiferous kimberlites and are used as mineralogic tracers by prospectors, who follow the indicator trail back to the volcanic pipe which may contain diamonds. These minerals are rich in chromium (Cr) or titanium (Ti), elements which impart bright colors to the minerals. The most common indicator minerals are chromian garnets (usually bright red Cr-pyrope, and occasionally green ugrandite-series garnets), eclogitic garnets, orange Ti-pyrope, red high-Cr spinels, dark chromite, bright green Cr-diopside, glassy green olivine, black picroilmenite, and magnetite.[11] Kimberlite deposits are known as blue ground for the deeper serpentinized part of the deposits, or as yellow ground for the near surface smectite clay and carbonate weathered and oxidized portion.
Once diamonds have been transported to the surface by magma in a volcanic pipe, they may erode out and be distributed over a large area. A volcanic pipe containing diamonds is known as a primary source of diamonds. Secondary sources of diamonds include all areas where a significant number of diamonds, eroded out of their kimberlite or lamproite matrix, and accumulated because of water or wind action. These include alluvial deposits and deposits along existing and ancient shorelines, where loose diamonds tend to accumulate because of their approximate size and density. Diamonds have also rarely been found in deposits left behind by glaciers (notably in Wisconsin and Indiana); however, in contrast to alluvial deposits, glacial deposits are not known to be of significant concentration and are therefore not viable commercial sources of diamond.
Commercial markets
A round brilliant cut diamond set in a ring
The diamond indust
ry can be broadly separated into two basically distinct categories: one dealing with gem-grade diamonds and another for industrial-grade diamonds. While a large trade in both types of diamonds exists, the two markets act in dramatically different ways.Gemstones
Main article: Diamond (gemstone)
A large trade in gem-grade diamonds exists. Unlike precious metals such as gold or platinum, gem diamonds do not trade as a commodity: there is a substantial mark-up in the retail sale of diamonds. Contrary to popular belief, there is a well-established market for resale of polished diamonds (e.g. pawnbroking, auctions, second-hand jewellery stores, diamantaires, bourses, etc.). One hallmark of the trade in gem-quality diamonds is its remarkable concentration: wholesale trade and diamond cutting is limited to just a few locations. 92% of diamond pieces cut in 2003 were in Surat, Gujarat, India.[27] Other important centers of diamond cutting and trading are Antwerp, where the International Gemological Institute is based, London, New York, Tel Aviv, and Amsterdam. A single company—De Beers—controls a significant proportion of the trade in diamonds. They are based in Johannesburg, South Africa and London, England. One contributory factor is the geological nature of diamond deposits: several large primary kimberlite-pipe mines each account for significant portions of market share (such as the Jwaneng mine in Botswana, which is a single large pit operated by De Beers that can produce between 12.5 to 15 million carats of diamonds per year[28]), whereas secondary alluvial diamond deposits tend to be fragmented amongst many different operators because they can be dispersed over many hundreds of square kilometres (e.g. alluvial deposits in Brazil).
The production and distribution of diamonds is largely consolidated in the hands of a few key players, and concentrated in traditional diamond trading centers. The most important being Antwerp, where 80% of all rough diamonds, 50% of all cut diamonds and more than 50% of all rough, cut and industrial diamonds combined are handled.[citation needed] This makes Antwerp the de facto 'world diamond capital'. New York, however, along with the rest of the United States, is where almost 80% of the world's diamonds are sold, including auction sales. Also, the largest and most unusually shaped rough diamonds end up in New York.[citation needed] The De Beers company, as the world's largest diamond miner holds a clearly dominant position in the industry, and has done so since soon after its founding in 1888 by the British imperialist Cecil Rhodes. De Beers owns or controls a significant portion of the world's rough diamond production facilities (mines) and distribution channels for gem-quality diamonds. The company and its subsidiaries own mines that produce some 40 percent of annual world diamond production. At one time it was thought over 80 percent of the world's rough diamonds passed through the Diamond Trading Company (DTC, a subsidiary of De Beers) in London[1], but presently the figure is estimated at around 40 percent[2]. De Beers sold off the vast majority its diamond stockpile in the late 1990s - early 2000s[3] and the remainder largely represents working stock (diamonds that are being sorted before sale)[4]. This was well-documented in the press[5] but remains little-known to the general public.
The De Beers diamond advertising campaign is acknowledged as one of the most successful and innovative campaigns in history. N. W. Ayer & Son, the advertising firm retained by De Beers in the mid-20th century, succeeded in reviving the American diamond market and opened up new markets, even in countries where no diamond tradition had existed before. N.W. Ayer's multifaceted marketing campaign included product placement, advertising the diamond itself rather than the De Beers brand, and building associations with celebrities and royalty. This coordinated campaign has lasted decades and continues today; it is perhaps best captured by the slogan "a diamond is forever".
Further down the supply chain, members of The World Federation of Diamond Bourses (WFDB) act as a medium for wholesale diamond exchange, trading both polished and rough diamonds. The WFDB consists of independent diamond bourses in major cutting centres such as Tel Aviv, Antwerp, Johannesburg and other cities across the USA, Europe and Asia.
In 2000, the WFDB and The International Diamond Manufacturers Association established the World Diamond Council to prevent the trading of diamonds used to fund war and inhumane acts.
WFDB's additional activities also include sponsoring the World Diamond Congress every two years, as well as the establishment of the International Diamond Council (IDC) to oversee diamond grading.
Industrial grade
Diamonds in an angle grinder blade
The market for industrial-grade diamonds operates much differently from its gem-grade counterpart. Industrial diamonds are valued mostly for their hardness and heat conductivity, making many of the gemological characteristics of diamonds, such as clarity and color, irrelevant for most applications. This helps explain why 80% of mined diamonds (equal to about 100 million carats or 20,000 kg annually), unsuitable for use as gemstones, are destined for industrial use. In addition to mined diamonds, synthetic diamonds found industrial applications almost immediately after their invention in the 1950s; another 3 billion carats (600 metric tons)[citation needed] of synthetic diamond is produced annually for industrial use. Approximately 90% of diamond grinding grit is currently of synthetic origin.
The dominant industrial use of diamond is in cutting, drilling, grinding, and polishing. Most uses of diamonds in these technologies do not require large diamonds; in fact, most diamonds that are gem-quality except for their small size, can find an industrial use. Diamonds are embedded in drill tips or saw blades, or ground into a powder for use in grinding and polishing applications. Specialized applications include use in laboratories as containment for high pressure experiments (see diamond anvil cell), high-performance bearings, and limited use in specialized windows.
With the continuing advances being made in the production of synthetic diamonds, future applications are beginning to become feasible. Garnering much excitement is the possible use of diamond as a semiconductor suitable to build microchips from, or the use of diamond as a heat sink in electronics.
The boundary between gem-quality diamonds and industrial diamonds is poorly-defined and partly depends on market conditions (for example, if demand for polished diamonds is high, some suitable stones will be polished into low-quality or small gemstones rather than being sold for industrial use). Within the category of industrial diamonds, there is a sub-category comprising the lowest-quality, mostly opaque stones, which are known as bort or 'boart'.
Supply chain
Diamond output in 2005
See also: List of diamond mines
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 can bring diamond crystals, originating from deep within the Earth where high pressures and temperatures enable them to form, to the surface. The mining and distribution of natural diamonds are subjects of frequent controversy such as with concerns over the sale of conflict diamonds (aka blood diamonds) by African paramilitary groups.
The diamond supply chain is controlled by a limited number of powerful businesses, and is also highly concentrated in a small number of locations around the world.
Mining, sources and production
Only a very small fraction of the diamond ore consists of actual diamonds. The ore is crushed, during which care has to be taken in order to prevent larger diamonds from being destroyed, and then sorted by density. Today, diamonds are located in the diamond-rich density fraction with the help of X-ray fluorescence, after which the final sorting steps are done by hand. Before the use of X-rays became commonplace, the separation was done with grease belts; diamonds have a stronger tendency to stick to grease than the other minerals in the ore.
Historically diamonds were known to be found only in alluvial deposits in southern India.[29] India led the world in diamond production from the time of their discovery in approximately the 9th century BCE[30][6] to the mid-18th century AD, but the commercial potential of these sources had been exhausted by the late 18th century and at that time India was eclipsed by Brazil where the first non-Indian diamonds were found in 1725.[6]
Diamond production of primary deposits (kimberlites and lamproites) only started in the 1870s after the discovery of the Diamond fields in South Africa. Production has increased over time and now an accumulated total of 4.5 billion carats have been mined since that date.[31] Interestingly 20% of that amount has been mined in the last 5 years alone and during the last ten years 9 new mines have started production while 4 more are waiting to be opened soon. Most of these mines are located in Canada, Zimbabwe, Angola, and one in Russia.[31]
In the U.S., diamonds have been found in Arkansas, Colorado, and Montana.[32][33] In 2004, a startling discovery of a microscopic diamond in the U.S.[34] led to the January 2008 bulk-sampling of kimberlite pipes in a remote part of Montana.[35]
Today, most commercially viable diamond deposits are in Russia (mostly in Yakutia, for example Mir pipe and Udachnaya pipe), Botswana, Australia (Northern and Western Australia) and the Democratic Republic of Congo.[36]
In 2005, Russia produced almost one-fifth of the global diamond output, reports the British Geological Survey. Australia boasts the richest diamondiferous pipe with production reaching peak levels of 42 metric tons (41 LT; 46 ST) per year in the 1990s.[32]
There are also commercial deposits being actively mined in the Northwest Territories of Canada and Brazil. Diamond prospectors continue to search the globe for diamond-bearing kimberlite and lamproite pipes.
Controversial sources
Main article: Blood diamond
In some of the more politically unstable central African and west African countries, revolutionary groups have taken control of diamond mines, using proceeds from diamond sales to finance their operations. Diamonds sold through this process are known as conflict diamonds or blood diamonds. Major diamond trading corporations continue to fund and fuel these conflicts by doing business with armed groups. In response to public concerns that their diamond purchases were contributing to war and human rights abuses in central and western Africa, the United Nations, the diamond industry and diamond-trading nations introduced the Kimberley Process in 2002. The Kimberley Process aims to ensure that conflict diamonds do not become intermixed with the diamonds not controlled by such rebel groups. This is done by requiring diamond-producing countries to provide proof that the money they make from selling the diamonds is not used to fund criminal or revolutionary activities. Although the Kimberley Process has been moderately successful in limiting the number of conflict diamonds entering the market, some still find their way in. 2–3% of all diamonds traded today are potentially conflict diamonds[37]. Two major flaws still hinder the effectiveness of the Kimberley Process: (1) the relative ease of smuggling diamonds across African borders, and (2) the violent nature of diamond mining in nations that are not in a technical state of war and whose diamonds are therefore considered "clean."[38]
The Canadian Government has set up a body known as Canadian Diamond Code of Conduct[39] to help authenticate Canadian diamonds. This is a very stringent tracking system of diamonds and helps protect the 'conflict free' label of Canadian diamonds.
Distribution
The Diamond Trading Company (DTC) is a subsidiary of De Beers and markets rough diamonds from De Beers-operated mines (it withdrew from purchasing diamonds on the open market in 1999 and ceased purchasing Russian diamonds mined by Russian company Alrosa, at the end of 2008 and, although Alrosa has successfully appealed against a European court ruling[6], according to a statement by an Alrosa spokesperson, sales do not appear to have resumed[7]).
Once purchased by Sightholders (which is a trademark term referring to the companies that have a three-year supply contract with DTC), diamonds are cut and polished in preparation for sale as gemstones. The cutting and polishing of rough diamonds is a specialized skill that is concentrated in a limited number of locations worldwide. Traditional diamond cutting centers are Antwerp, Amsterdam, Johannesburg, New York, and Tel Aviv. Recently, diamond cutting centers have been established in China, India, Thailand, Namibia and Botswana. Cutting centers with lower cost of labor, notably Surat in Gujarat, India, handle a larger number of smaller carat diamonds, while smaller quantities of larger or more valuable diamonds are more likely to be handled in Europe or North America. The recent expansion of this industry in India, employing low cost labor, has allowed smaller diamonds to be prepared as gems in greater quantities than was previously economically feasible.
Diamonds which have been prepared as gemstones are sold on diamond exchanges called bourses. There are 26 registered diamond bourses in the world.[40] Bourses are the final tightly controlled step in the diamond supply chain; wholesalers and even retailers are able to buy relatively small lots of diamonds at the bourses, after which they are prepared for final sale to the consumer. Diamonds can be sold already set in jewelry, or sold unset ("loose"). According to the Rio Tinto Group, in 2002 the diamonds produced and released to the market were valued at US$9 billion as rough diamonds, US$14 billion after being cut and polished, US$28 billion in wholesale diamond jewelry, and US$57 billion in retail sales.
Synthetics, simulants, and enhancements
Main articles: Synthetic diamond, Diamond simulant, and Diamond enhancement
Synthetics
Synthetic diamonds are diamond crystals that are manufactured in a laboratory, as opposed to natural diamonds which form naturally within the earth.
The gemological and industrial uses of diamond have created a large demand for rough stones. This demand has long been satisfied in large part by synthetic diamonds, which have been manufactured by various processes for more than half a century. However, in recent years it has become possible to produce gem-quality synthetic diamonds of significant size.[41]
The majority of commercially available synthetic diamonds are yellow in color and produced by so called High Pressure High Temperature (HPHT) processes.[42] The yellow color is caused by nitrogen impurities. Other colors may also be reproduced such as blue, green or pink which are a result of the addition of boron or from irradiation after synthesis.[43]
At present, the annual production of gem quality synthetic diamonds is only a few thousand carats, whereas the total production of natural diamonds is around 120 million carats. Despite this fact, a purchaser is more likely to encounter a synthetic when looking for a fancy-colored diamond because nearly all synthetic diamonds are fancy-colored, while only 0.01% of natural diamonds are fancy-colored.[44]
Producing large synthetic diamonds threatens the business model of the diamond industry. The ultimate effect of the ready availability of gem-quality diamonds at low cost in the future is hard to predict.
Simulants
A diamond simulant is defined as a non-diamond material that is used to simulate the appearance of a diamond. Diamond-simulant gems are often referred to as diamante.
The most familiar diamond simulant to most consumers is cubic zirconia (commonly abbreviated as CZ). The popular gemstone moissanite is often mischaracterized as a diamond simulant, although it is marketed as a gemstone in its own right rather than explicitly as a diamond simulant. While moissanite does look similar to diamond, its main disadvantage as a diamond simulant is that CZ is far cheaper and arguably equally convincing. Both CZ and moissanite are synthetically produced.
Enhancements
Diamond enhancements are specific treatments performed on natural or synthetic diamonds (usually those already cut and polished into a gem), which are designed to better the gemological characteristics of the stone in one or more ways. These include laser drilling to remove inclusions, application of sealants to fill cracks, treatments to improve a white diamond's color grade, and treatments to give fancy color to a white diamond.
Coatings are increasingly used to give a diamond simulant such as cubic zirconia a more "diamond-like" appearance. One such substance, which is heavily advertised, is what scientists refer to as "diamond-like carbon". This is an amorphous carbonaceous material that has some physical properties which are similar to that of the diamond. Advertising suggests that such a coating would transfer some of these diamond-like properties to the coated stone, hence enhancing the diamond simulant. However, modern techniques such as Raman Spectroscopy should easily identify such as treatment.[45]
Identification
In the 22 November 2008 issue of New Scientist, it was stated that Russell Hemley of the Geophysical Laboratory at the Carnegie Institution for Science had discovered a technique to make diamonds via microwaves which were indistiguishable from natural diamonds. Yufei Meng, a scientist from the same laboratory, claimed that after having sent these diamonds for diamond jewellery identification, they were not identified as different from natural diamonds.[citation needed] Such claims are often made for new synthetics, simulants, and treated stones, so it is important to validate how the stones were submitted for identification. For example, the "test" could simply refer to showing the stones to an unqualified jewellery shop assistant.
Properly-trained and equipped gemologists can distinguish between natural diamonds and synthetic diamonds. They can also identify the vast majority of treated natural diamonds, two exceptions being a small minority of HPHT-treated Type II diamonds and some artificially-irradiated green diamonds. "Perfect" crystals (at the atomic lattice level) have never been found to exist anywhere, so both natural and synthetic diamonds always possess characteristic imperfections, arising from the circumstances of their crystal growth, that allow them to be distinguished from each other.
Laboratories use techniques such as spectroscopy, microscopy and luminescence under shortwave ultraviolet light to determine a diamond's origin. They also use specially-made machines to aid them in the identification process. Two screening machines are the DiamondSure and the DiamondView, both produced by the DTC and marketed by the GIA.[46]
Several methods for identifying synthetic diamonds can be performed, depending on the method of production and the color of the diamond. CVD diamonds can usually be identified by an orange fluorescence. D-J colored diamonds can be screened through the Swiss Gemological Organization's[47] Diamond Spotter. Stones in the D-Z color range can be examined through the DiamondSure UV/visible spectrometer which is a tool developed by De Beers.[48] Similarly, natural diamonds usually have minor imperfections and flaws, such as inclusions of foreign material, that are not seen in synthetic diamonds
No comments:
Post a Comment