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Diamond: the story on HearLore | HearLore
Diamond
Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. This arrangement creates a material that is tasteless, odorless, strong, and brittle, appearing colorless in its purest form. It is a poor conductor of electricity and insoluble in water, yet it possesses the highest hardness and thermal conductivity of any natural material. These properties have made it indispensable for major industrial applications such as cutting and polishing tools. While another solid form of carbon known as graphite is the chemically stable form at room temperature and pressure, diamond remains metastable and converts to it at a negligible rate under those conditions. The rigidity of the atomic arrangement means that few types of impurity can contaminate it, with boron and nitrogen being the primary exceptions. Small numbers of defects or impurities, about one per million of lattice atoms, can color a diamond blue, yellow, brown, green, purple, pink, orange, or red. The material also has a very high refractive index and a relatively high optical dispersion, giving it its characteristic sparkle.
The name diamond is derived from the Greek word adamas, meaning proper, unalterable, unbreakable, or untamed. Diamonds are thought to have been first recognized and mined in India, where significant alluvial deposits of the stone could be found many centuries ago along the rivers Penner, Krishna, and Godavari. Diamonds have been known in India for at least 3,000 years but most likely 6,000 years. They have been treasured as gemstones since their use as religious icons in ancient India, and their usage in engraving tools also dates to early human history. The 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. In 1772, the French scientist Antoine Lavoisier 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. Later, in 1797, the English chemist Smithson Tennant repeated and expanded that experiment. By demonstrating that burning diamond and graphite releases the same amount of gas, he established the chemical equivalence of these substances.
The Deep Earth Journey
Most natural diamonds have ages between 1 billion and 3.5 billion years. Most were formed at depths between 150 and 250 kilometers in the Earth's mantle, although a few have come from as deep as 800 kilometers. Under high pressure and temperature, carbon-containing fluids dissolved various minerals and replaced them with diamonds. Much more recently, hundreds to tens of millions of years ago, they were carried to the surface in volcanic eruptions and deposited in igneous rocks known as kimberlites and lamproites. A common misconception is that diamonds form from highly compressed coal. Coal is formed from buried prehistoric plants, and most diamonds that have been dated are far older than the first land plants. It is possible that diamonds can form from coal in subduction zones, but diamonds formed in this way are rare, and the carbon source is more likely carbonate rocks and organic carbon in sediments, rather than coal.
Geological evidence supports a model in which kimberlite magma rises at 4 to 20 meters per second, creating an upward path by hydraulic fracturing of the rock. As the pressure decreases, a vapor phase exsolves from the magma, and this helps to keep the magma fluid. At the surface, the initial eruption explodes out through fissures at high speeds. Then, at lower pressures, the rock is eroded, forming a pipe and producing fragmented rock. The host rocks in a mantle keel include harzburgite and lherzolite, two types of peridotite. Another common source that does keep diamonds intact is eclogite, a metamorphic rock that typically forms from basalt as an oceanic plate plunges into the mantle at a subduction zone. A smaller fraction of diamonds come from depths of 330 to 660 kilometers, a region that includes the transition zone. They formed in eclogite but are distinguished from diamonds of shallower origin by inclusions of majorite. A similar proportion of diamonds comes from the lower mantle at depths between 660 and 800 kilometers. In 2018, the first known natural samples of a phase of ice called Ice VII were found as inclusions in diamond samples. The inclusions formed at depths between 400 and 800 kilometers, straddling the upper and lower mantle, and provide evidence for water-rich fluid at these depths.
Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. It is composed entirely of carbon atoms and is insoluble in water. The material is a poor conductor of electricity and possesses the highest hardness and thermal conductivity of any natural material.
Where were diamonds first recognized and mined?
Diamonds are thought to have been first recognized and mined in India, where significant alluvial deposits could be found along the rivers Penner, Krishna, and Godavari. Diamonds have been known in India for at least 3,000 years but most likely 6,000 years. They were treasured as gemstones since their use as religious icons in ancient India.
How old are most natural diamonds?
Most natural diamonds have ages between 1 billion and 3.5 billion years. They were formed at depths between 150 and 250 kilometers in the Earth's mantle, although a few have come from as deep as 800 kilometers. They were carried to the surface in volcanic eruptions and deposited in igneous rocks known as kimberlites and lamproites.
What causes the color in diamonds?
Colors in diamond originate from lattice defects and impurities such as nitrogen, boron, and hydrogen. Nitrogen is responsible for the yellow and brown color in diamonds, while boron is responsible for the blue color. Irradiation and plastic deformation of the diamond crystal lattice also cause colors such as green, brown, pink, and red.
When was the Kimberley Process introduced?
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 diamonds not controlled by rebel groups. According to the International Diamond Manufacturers Association, conflict diamonds constitute 2 to 3% of all diamonds traded.
Which city handles the majority of rough diamonds?
Antwerp is the de facto world diamond capital 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. The city also hosts the Antwerpsche Diamantkring, created in 1929 to become the first and biggest diamond bourse dedicated to rough diamonds. New York City is another important center where almost 80% of the world's diamonds are sold.
The hardest natural diamonds mostly originate from the Copeton and Bingara fields located in the New England area in New South Wales, Australia. These diamonds are generally small, perfect to semiperfect octahedra, and are used to polish other diamonds. Their hardness is associated with the crystal growth form, which is single-stage crystal growth. 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. 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. The toughness of natural diamond has been measured as 50 to 65 MPa·m1/2. This value is good compared to other ceramic materials, but poor compared to most engineering materials such as engineering alloys, which typically exhibit toughness over 80 MPa·m1/2. 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 before faceting them.
Diamond has a wide band gap of 5.5 electron volts corresponding to the deep ultraviolet wavelength of 225 nanometers. This means that pure diamond should transmit visible light and appear as a clear colorless crystal. Colors in diamond originate from lattice defects and impurities. The diamond crystal lattice is exceptionally strong, and only atoms of nitrogen, boron, and hydrogen can be introduced into diamond during the growth at significant concentrations. Transition metals nickel and cobalt, which are commonly used for growth of synthetic diamond by high-pressure high-temperature techniques, have been detected in diamond as individual atoms. Virtually any element can be introduced to diamond by ion implantation. Nitrogen is by far the most common impurity found in gem diamonds and is responsible for the yellow and brown color in diamonds. Boron is responsible for the blue color. Color in diamond has two additional sources: irradiation, usually by alpha particles, that causes the color in green diamonds, and plastic deformation of the diamond crystal lattice. Plastic deformation is the cause of color in some brown and perhaps pink and red diamonds.
In order
The Color of Impurity
of increasing rarity, yellow diamond is followed by brown, colorless, then by blue, green, black, pink, orange, purple, and red. 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. In 2008, the Wittelsbach Diamond, a blue diamond once belonging to the King of Spain, fetched over US$24 million at a Christie's auction. In May 2009, a blue diamond fetched the highest price per carat ever paid for a diamond when it was sold at auction for 10.5 million Swiss francs. That record was, however, beaten the same year: a vivid pink diamond was sold for US$10.8 million in Hong Kong on the 1st of December 2009. Between 25% and 35% of natural diamonds exhibit some degree of fluorescence when examined under invisible long-wave ultraviolet light or higher energy radiation sources such as X-rays and lasers. Diamonds can fluoresce in a variety of colors including blue, orange, yellow, white, green, and very rarely red and purple.
The most familiar uses of diamonds today are as gemstones used for adornment, and as industrial abrasives for cutting hard materials. The markets for gem-grade and industrial-grade diamonds value diamonds differently. A large trade in gem-grade diamonds exists. Although most gem-grade diamonds are sold newly polished, there is a well-established market for resale of polished diamonds. 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. In 2003, 92% of the world's diamonds were cut and polished in Surat, India. Other important centers of diamond cutting and trading are the Antwerp diamond district in Belgium, where the International Gemological Institute is based, London, the Diamond District in New York City, the Diamond Exchange District in Tel Aviv and Amsterdam. The De Beers company, as the world's largest diamond mining company, holds a dominant position in the industry, and has done so since soon after its founding in 1888 by the British businessman Cecil Rhodes. De Beers is currently the world's largest operator of diamond production facilities and distribution
The Global Trade Web
channels for gem-quality diamonds.
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. This makes Antwerp a de facto world diamond capital. The city of Antwerp also hosts the Antwerpsche Diamantkring, created in 1929 to become the first and biggest diamond bourse dedicated to rough diamonds. Another important diamond center is New York City, where almost 80% of the world's diamonds are sold, including auction sales. As a part of reducing its influence, De Beers withdrew from purchasing diamonds on the open market in 1999 and ceased, at the end of 2008, purchasing Russian diamonds mined by the largest Russian diamond company Alrosa. As of January 2011, De Beers states that it only sells diamonds from the following four countries: Botswana, Namibia, South Africa and Canada. Apart from Alrosa, other important diamond mining companies include BHP, which is the world's largest mining company; Rio Tinto, the owner of the Argyle, Diavik, and Murowa diamond mines; and Petra Diamonds, the owner of several major diamond mines in Africa.
Mined rough diamonds are converted into gems through a multi-step process called cutting. Diamonds are extremely hard, but also brittle and can be split up by a single blow. Therefore, diamond cutting is traditionally considered as a delicate procedure requiring skills, scientific knowledge, tools and experience. Its final goal is to produce a faceted jewel where the specific angles between the facets would optimize the diamond luster, that is dispersion of white light, whereas the number and area of facets would determine the weight of the final product. The weight reduction upon cutting is significant and can be of the order of 50%. Several possible shapes are considered, but the final decision is often determined not only by scientific, but also practical considerations. For example, the diamond might be intended for display or for wear, in a ring or a necklace, singled or surrounded by other gems of certain color and shape. Some of them may be considered as classical, such as round, pear, marquise, oval, hearts and arrows diamonds. Some of them are special, produced by certain companies, for example, Phoenix,
The Cutting Edge
Cushion, Sole Mio diamonds.
The most time-consuming part of the cutting is the preliminary analysis of the rough stone. It needs to address a large number of issues, bears much responsibility, and therefore can last years in case of unique diamonds. The following issues are considered: the hardness of diamond and its ability to cleave strongly depend on the crystal orientation. Therefore, the crystallographic structure of the diamond to be cut is analyzed using X-ray diffraction to choose the optimal cutting directions. Most diamonds contain visible non-diamond inclusions and crystal flaws. The cutter has to decide which flaws are to be removed by the cutting and which could be kept. Splitting a diamond with a hammer is difficult, a well-calculated, angled blow can cut the diamond, piece-by-piece, but it can also ruin the diamond itself. Alternatively, it can be cut with a diamond saw, which is a more reliable method. After initial cutting, the diamond is shaped in numerous stages of polishing. Unlike cutting, which is a responsible but quick operation, polishing removes material by gradual erosion and is extremely time-consuming. The associated technique is well developed; it is considered as a routine and can be performed by technicians. After polishing, the diamond is reexamined for possible flaws, either remaining or induced by the process. Those flaws are concealed through various diamond enhancement techniques, such as repolishing, crack filling, or clever arrangement of the stone in the jewelry. Remaining non-diamond inclusions are removed through laser drilling and filling of the voids produced.
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. In response to public concerns that their diamond purchases were contributing to war and human rights abuses, 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. According to the International Diamond Manufacturers Association, conflict diamonds constitute 2 to 3% of all diamonds traded. Two major flaws still hinder the effectiveness of the Kimberley Process: the relative ease of smuggling
The Blood and The Black Market
diamonds across African borders, and the violent nature of diamond mining in nations that are not in a technical state of war and whose diamonds are therefore considered clean.
The Canadian Government has set up a body known as the Canadian Diamond Code of Conduct to help authenticate Canadian diamonds. This is a stringent tracking system of diamonds and helps protect the conflict free label of Canadian diamonds. Mineral resource exploitation in general causes irreversible environmental damage, which must be weighed against the socio-economic benefits to a country. Approximately 140 million carats of diamonds are mined annually, with a total value of nearly US$9 billion, and about 133 million carats are synthesized annually. 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. Historically, diamonds were found only in alluvial deposits in Guntur and Krishna district of the Krishna River delta in Southern India. India led the world in diamond production from the time of their discovery in approximately the 9th century BC 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. Currently, one of the most prominent Indian mines is located at Panna.
Synthetic diamonds are diamonds manufactured in a laboratory, as opposed to diamonds mined from the Earth. The gemological and industrial uses of diamond have created a large demand for rough stones. This demand has 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. It is possible to make colorless synthetic gemstones that, on a molecular level, are identical to natural stones and so visually similar that only a gemologist with special equipment can tell the difference. The majority of commercially available synthetic diamonds are yellow and are produced by so-called high-pressure high-temperature processes. 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.
Another popular method of growing synthetic diamond is chemical vapor deposition. The growth occurs under low pressure, below atmospheric pressure. It involves feeding a mixture of gases,
The Synthetic Revolution
typically methane to hydrogen, into a chamber and splitting them into chemically active radicals in a plasma ignited by microwaves, hot filament, arc discharge, welding torch, or laser. This method is mostly used for coatings, but can also produce single crystals several millimeters in size. As of 2010, nearly all 5,000 million carats of synthetic diamonds produced per year are for industrial use. Around 50% of the 133 million carats of natural diamonds mined per year end up in industrial use. Mining companies' expenses average 40 to 60 US dollars per carat for natural colorless diamonds, while synthetic manufacturers' expenses average 10 to 20 US dollars for synthetic, gem-quality colorless diamonds. However, a purchaser is more likely to encounter a synthetic when looking for a fancy-colored diamond because only 0.01% of natural diamonds are fancy-colored, while most synthetic diamonds are colored in some way. A diamond simulant is a non-diamond material that is used to simulate the appearance of a diamond, and may be referred to as diamante. Cubic zirconia is the most common. The gemstone moissanite, silicon carbide, can be treated as a diamond simulant, though more costly to produce than cubic zirconia. Both are produced synthetically.