Diamond

Diamond is a

Most natural diamonds have ages between 1 billion and 3.5 billion years. Most were formed at depths between 150 and 250 kilometres (93 and 155 mi) in the Earth's mantle, although a few have come from as deep as 800 kilometres (500 mi). Under high pressure and temperature, carbon-containing fluids dissolved various minerals and replaced them with diamonds. Much more recently (hundreds to tens of million years ago), they were carried to the surface in volcanic eruptions and deposited in igneous rocks known as kimberlites and lamproites.

Synthetic diamonds can be grown from high-purity carbon under high pressures and temperatures or from hydrocarbon gases by chemical vapor deposition (CVD). Natural and synthetic diamonds are most commonly distinguished using optical techniques or thermal conductivity measurements. ^{[citation needed]}

Diamond is a solid form of pure carbon with its atoms arranged in a crystal. Solid carbon comes in different forms known as

The equilibrium pressure and temperature conditions for a transition between graphite and diamond are well established theoretically and experimentally. The equilibrium pressure varies linearly with temperature, between 1.7 

Rapid conversion of graphite to diamond requires pressures well above the equilibrium line: at 2000 K, a pressure of 35 GPa (about 350,000 standard atmospheres) is needed.[10]

Above the graphite–diamond–liquid carbon triple point, the melting point of diamond increases slowly with increasing pressure; but at pressures of hundreds of GPa, it decreases.^[14] At high pressures, silicon and germanium have a BC8 body-centered cubic crystal structure, and a similar structure is predicted for carbon at high pressures. At 0 K, the transition is predicted to occur at 1100 GPa.^[15]

Results published in Nature Physics in 2010 suggest that, at ultra-high pressures and temperatures (about 10 million atmospheres or 1 TPa and 50,000 °C), diamond melts into a metallic fluid. The extreme conditions required for this to occur are present in the ice giant planets Neptune and Uranus, both of which are made up of approximately 10 percent carbon and could hypothetically contain oceans of liquid carbon. Since large quantities of metallic fluid can affect the magnetic field, this could serve to explain why the geographic and magnetic poles of the two planets are not aligned.^[16][17]

The most common crystal structure of diamond is called diamond cubic. It is formed of unit cells (see the figure) stacked together. Although there are 18 atoms in the figure, each corner atom is shared by eight unit cells and each atom in the center of a face is shared by two, so there are a total of eight atoms per unit cell.^[18] The length of each side of the unit cell is denoted by a and is 3.567 angstroms.^[19]

The nearest neighbor distance in the diamond lattice is 1.732a/4 where a is the lattice constant, usually given in Angstrøms as a = 3.567 Å, which is 0.3567 nm.

A diamond cubic lattice can be thought of as two interpenetrating

Diamonds occur most often as

Some diamonds contain opaque fibers. They are referred to as opaque if the fibers grow from a clear substrate or fibrous if they occupy the entire crystal. Their colors range from yellow to green or gray, sometimes with cloud-like white to gray impurities. Their most common shape is cuboidal, but they can also form octahedra, dodecahedra, macles, or combined shapes. The structure is the result of numerous impurities with sizes between 1 and 5 microns. These diamonds probably formed in kimberlite magma and sampled the volatiles.[22]

Diamonds can also form polycrystalline aggregates. There have been attempts to classify them into groups with names such as

Diamond is the hardest material on the

Diamond hardness depends on its purity, crystalline perfection, and orientation: hardness is higher for flawless, pure crystals oriented to the <111> direction (along the longest diagonal of the cubic diamond lattice).^[29] Therefore, whereas it might be possible to scratch some diamonds with other materials, such as boron nitride, the hardest diamonds can only be scratched by other diamonds and nanocrystalline diamond aggregates.

The hardness of diamond 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.

The hardest natural diamonds mostly originate from the

Diamonds cut glass, but this does not positively identify a diamond because other materials, such as quartz, also lie above glass on the Mohs scale and can also cut it. Diamonds can scratch other diamonds, but this can result in damage to one or both stones. Hardness tests are infrequently used in practical gemology because of their potentially destructive nature.^[31] The extreme hardness and high value of diamond means that gems are typically polished slowly, using painstaking traditional techniques and greater attention to detail than is the case with most other gemstones;^[32] these tend to result in extremely flat, highly polished facets with exceptionally sharp facet edges. Diamonds also possess an extremely high refractive index and fairly high dispersion. Taken together, these factors affect the overall appearance of a polished diamond and most diamantaires still rely upon skilled use of a loupe (magnifying glass) to identify diamonds "by eye".^[33]

Somewhat related to hardness is another mechanical property toughness, which is a material's ability to resist breakage from forceful impact. The

Usually, attempting to deform bulk diamond crystal by tension or bending results in brittle fracture. However, when single crystalline diamond is in the form of micro/nanoscale wires or needles (~100–300 nanometers in diameter, micrometers long), they can be elastically stretched by as much as 9–10 percent tensile strain without failure,[40] with a maximum local tensile stress of about 89–98 GPa,^[41] very close to the theoretical limit for this material.^[42]

Other specialized applications also exist or are being developed, including use as

Thin needles of diamond can be made to vary their electronic band gap from the normal 5.6 eV to near zero by selective mechanical deformation.^[46]

High-purity diamond wafers 5 cm in diameter exhibit perfect resistance in one direction and perfect conductance in the other, creating the possibility of using them for quantum data storage. The material contains only 3 parts per million of nitrogen. The diamond was grown on a stepped substrate, which eliminated cracking.^[47]

Diamonds are naturally lipophilic and hydrophobic, which means the diamonds' surface cannot be wet by water, but can be easily wet and stuck by oil. This property can be utilized to extract diamonds using oil when making synthetic diamonds. However, when diamond surfaces are chemically modified with certain ions, they are expected to become so hydrophilic that they can stabilize multiple layers of water ice at human body temperature.^[48]

The surface of diamonds is partially oxidized. The oxidized surface can be reduced by heat treatment under hydrogen flow. That is to say, this heat treatment partially removes oxygen-containing functional groups. But diamonds (sp³C) are unstable against high temperature (above about 400 °C (752 °F)) under atmospheric pressure. The structure gradually changes into sp²C above this temperature. Thus, diamonds should be reduced below this temperature.^[49]

At room temperature, diamonds do not react with any chemical reagents including strong acids and bases.

In an atmosphere of pure oxygen, diamond has an

Diamond powder of an appropriate grain size (around 50 microns) burns with a shower of sparks after ignition from a flame. Consequently, pyrotechnic compositions based on synthetic diamond powder can be prepared. The resulting sparks are of the usual red-orange color, comparable to charcoal, but show a very linear trajectory which is explained by their high density.^[54] Diamond also reacts with fluorine gas above about 700 °C (1,292 °F).

Diamond has a wide band gap of 5.5 eV 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 (up to atomic percents). 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; the maximum concentration is 0.01% for nickel^[55] and even less for cobalt. Virtually any element can be introduced to diamond by ion implantation.^[56]

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.

Clarity is one of the 4C's (color, clarity, cut and carat weight) that helps in identifying the quality of diamonds. The Gemological Institute of America (GIA) developed 11 clarity scales to decide the quality of a diamond for its sale value. The GIA clarity scale spans from Flawless (FL) to included (I) having internally flawless (IF), very, very slightly included (VVS), very slightly included (VS) and slightly included (SI) in between. Impurities in natural diamonds are due to the presence of natural minerals and oxides. The clarity scale grades the diamond based on the color, size, location of impurity and quantity of clarity visible under 10x magnification.^[63] Inclusions in diamond can be extracted by optical methods. The process is to take pre-enhancement images, identifying the inclusion removal part and finally removing the diamond facets and noises.^[64]

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.^[65] Incandescent lighting will not cause a diamond to fluoresce. Diamonds can fluoresce in a variety of colors including blue (most common), orange, yellow, white, green and very rarely red and purple. Although the causes are not well understood, variations in the atomic structure, such as the number of nitrogen atoms present are thought to contribute to the phenomenon.

Diamonds can be identified by their high thermal conductivity (900–2320 W·m⁻¹·K⁻¹).^[66] Their high refractive index is also indicative, but other materials have similar refractivity.

Diamonds are extremely rare, with concentrations of at most parts per billion in source rock.

Most diamonds come from the Earth's mantle, and most of this section discusses those diamonds. However, there are other sources. Some blocks of the crust, or terranes, have been buried deep enough as the crust thickened so they experienced ultra-high-pressure metamorphism. These have evenly distributed microdiamonds that show no sign of transport by magma. In addition, when meteorites strike the ground, the shock wave can produce high enough temperatures and pressures for microdiamonds and nanodiamonds to form.^[68] Impact-type microdiamonds can be used as an indicator of ancient impact craters.^[69] Popigai impact structure in Russia may have the world's largest diamond deposit, estimated at trillions of carats, and formed by an asteroid impact.^[70]

A common misconception is that diamonds form from highly compressed

Diamonds are far from evenly distributed over the Earth. A rule of thumb known as Clifford's rule states that they are almost always found in

All three of the diamond-bearing rocks (kimberlite, lamproite and lamprophyre) lack certain minerals (melilite and kalsilite) that are incompatible with diamond formation. In kimberlite, olivine is large and conspicuous, while lamproite has Ti-phlogopite and lamprophyre has biotite and amphibole. They are all derived from magma types that erupt rapidly from small amounts of melt, are rich in volatiles and magnesium oxide, and are less oxidizing than more common mantle melts such as basalt. These characteristics allow the melts to carry diamonds to the surface before they dissolve.^[68]

Kimberlite pipes can be difficult to find. They weather quickly (within a few years after exposure) and tend to have lower topographic relief than surrounding rock. If they are visible in outcrops, the diamonds are never visible because they are so rare. In any case, kimberlites are often covered with vegetation, sediments, soils, or lakes. In modern searches, geophysical methods such as aeromagnetic surveys, electrical resistivity, and gravimetry, help identify promising regions to explore. This is aided by isotopic dating and modeling of the geological history. Then surveyors must go to the area and collect samples, looking for kimberlite fragments or indicator minerals. The latter have compositions that reflect the conditions where diamonds form, such as extreme melt depletion or high pressures in eclogites. However, indicator minerals can be misleading; a better approach is geothermobarometry, where the compositions of minerals are analyzed as if they were in equilibrium with mantle minerals.^[68]

Finding kimberlites requires persistence, and only a small fraction contain diamonds that are commercially viable. The only major discoveries since about 1980 have been in Canada. Since existing mines have lifetimes of as little as 25 years, there could be a shortage of new natural diamonds in the future.^[68]

Diamonds are dated by analyzing inclusions using the decay of radioactive isotopes. Depending on the elemental abundances, one can look at the decay of rubidium to strontium, samarium to neodymium, uranium to lead, argon-40 to argon-39, or rhenium to osmium. Those found in kimberlites have ages ranging from 1 to 3.5 billion years, and there can be multiple ages in the same kimberlite, indicating multiple episodes of diamond formation. The kimberlites themselves are much younger. Most of them have ages between tens of millions and 300 million years old, although there are some older exceptions (Argyle, Premier and Wawa). Thus, the kimberlites formed independently of the diamonds and served only to transport them to the surface.^[22][68] Kimberlites are also much younger than the cratons they have erupted through. The reason for the lack of older kimberlites is unknown, but it suggests there was some change in mantle chemistry or tectonics. No kimberlite has erupted in human history.^[68]

Most gem-quality diamonds come from depths of 150–250 km in the lithosphere. Such depths occur below cratons in mantle keels, the thickest part of the lithosphere. These regions have high enough pressure and temperature to allow diamonds to form and they are not convecting, so diamonds can be stored for billions of years until a kimberlite eruption samples them.^[68]

Host rocks in a mantle keel include

A smaller fraction of diamonds (about 150 have been studied) come from depths of 330–660 km, a region that includes the transition zone. They formed in eclogite but are distinguished from diamonds of shallower origin by inclusions of majorite (a form of garnet with excess silicon). A similar proportion of diamonds comes from the lower mantle at depths between 660 and 800 km.^[22]

Diamond is thermodynamically stable at high pressures and temperatures, with the phase transition from graphite occurring at greater temperatures as the pressure increases. Thus, underneath continents it becomes stable at temperatures of 950 degrees Celsius and pressures of 4.5 gigapascals, corresponding to depths of 150 kilometers or greater. In subduction zones, which are colder, it becomes stable at temperatures of 800 °C and pressures of 3.5 gigapascals. At depths greater than 240 km, iron–nickel metal phases are present and carbon is likely to be either dissolved in them or in the form of carbides. Thus, the deeper origin of some diamonds may reflect unusual growth environments.^[22][68]

In 2018 the first known natural samples of a phase of ice called

The mantle has roughly one billion gigatonnes of carbon (for comparison, the atmosphere-ocean system has about 44,000 gigatonnes).^[79] Carbon has two stable isotopes, ¹²C and ¹³C, in a ratio of approximately 99:1 by mass.^[68] This ratio has a wide range in meteorites, which implies that it also varied a lot in the early Earth. It can also be altered by surface processes like photosynthesis. The fraction is generally compared to a standard sample using a ratio δ¹³C expressed in parts per thousand. Common rocks from the mantle such as basalts, carbonatites, and kimberlites have ratios between −8 and −2. On the surface, organic sediments have an average of −25 while carbonates have an average of 0.^[22]

Populations of diamonds from different sources have distributions of δ¹³C that vary markedly. Peridotitic diamonds are mostly within the typical mantle range; eclogitic diamonds have values from −40 to +3, although the peak of the distribution is in the mantle range. This variability implies that they are not formed from carbon that is primordial (having resided in the mantle since the Earth formed). Instead, they are the result of tectonic processes, although (given the ages of diamonds) not necessarily the same tectonic processes that act in the present.^[68] Diamond-forming carbon originates in the top 700 kilometers (430 mi) or so of the upper mantle closest to the surface, known as the asthenosphere.^[22]

Diamonds in the mantle form through a metasomatic process where a C–O–H–N–S fluid or melt dissolves minerals in a rock and replaces them with new minerals. (The vague term C–O–H–N–S is commonly used because the exact composition is not known.) Diamonds form from this fluid either by reduction of oxidized carbon (e.g., CO₂ or CO₃) or oxidation of a reduced phase such as methane.^[22]

Using probes such as polarized light, photoluminescence, and cathodoluminescence, a series of growth zones can be identified in diamonds. The characteristic pattern in diamonds from the lithosphere involves a nearly concentric series of zones with very thin oscillations in luminescence and alternating episodes where the carbon is resorbed by the fluid and then grown again. Diamonds from below the lithosphere have a more irregular, almost polycrystalline texture, reflecting the higher temperatures and pressures as well as the transport of the diamonds by convection.^[68]

Geological evidence supports a model in which kimberlite magma rises at 4–20 meters per second, creating an upward path by

In rare cases, diamonds have been found that contain a cavity within which is a second diamond. The first double diamond, the Matryoshka, was found by Alrosa in Yakutia, Russia, in 2019.^[80] Another one was found in the Ellendale Diamond Field in Western Australia in 2021.^[81]

Although diamonds on Earth are rare, they are very common in space. In meteorites, about three percent of the carbon is in the form of nanodiamonds, having diameters of a few nanometers. Sufficiently small diamonds can form in the cold of space because their lower surface energy makes them more stable than graphite. The isotopic signatures of some nanodiamonds indicate they were formed outside the Solar System in stars.^[82]

High pressure experiments predict that large quantities of diamonds condense from methane into a "diamond rain" on the ice giant planets Uranus and Neptune.^[83][84][85] Some extrasolar planets may be almost entirely composed of diamond.^[86]

Diamonds may exist in carbon-rich stars, particularly white dwarfs. One theory for the origin of carbonado, the toughest form of diamond, is that it originated in a white dwarf or supernova.^[87][88] Diamonds formed in stars may have been the first minerals.^[89]

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.

The

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.^[93] This makes Antwerp a de facto "world diamond capital".^[94] The city of Antwerp also hosts the Antwerpsche Diamantkring, created in 1929 to become the first and biggest diamond bourse dedicated to rough diamonds.^[95] Another important diamond center is New York City, where almost 80% of the world's diamonds are sold, including auction sales.^[93]

The

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.^[102] As of January 2011, De Beers states that it only sells diamonds from the following four countries: Botswana, Namibia, South Africa and Canada.^[103] Alrosa had to suspend their sales in October 2008 due to the global energy crisis,^{[citation needed]} but the company reported that it had resumed selling rough diamonds on the open market by October 2009.^[104] Apart from Alrosa, other important diamond mining companies include BHP, which is the world's largest mining company;^[105] Rio Tinto, the owner of the Argyle (100%), Diavik (60%), and Murowa (78%) diamond mines;^[106] and Petra Diamonds, the owner of several major diamond mines in Africa.

Further down the supply chain, members of The

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 ('industrial' stones are regarded as a by-product of the gemstone market; they are used for abrasives).[108] The cutting and polishing of rough diamonds is a specialized skill that is concentrated in a limited number of locations worldwide.^[108] Traditional diamond cutting centers are Antwerp, Amsterdam, Johannesburg, New York City, and Tel Aviv. Recently, diamond cutting centers have been established in China, India, Thailand, Namibia and Botswana.^[108] 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.^[93]

Diamonds prepared as gemstones are sold on diamond exchanges called bourses. There are 28 registered diamond bourses in the world.^[109] 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, 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.^[110]

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%.

• 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.^[112][114]

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.[115] 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.^[31]

Marketing has significantly affected the image of diamond as a valuable commodity.

Brown-colored diamonds constituted a significant part of the diamond production, and were predominantly used for industrial purposes. They were seen as worthless for jewelry (not even being assessed on the diamond color scale). After the development of Argyle diamond mine in Australia in 1986, and marketing, brown diamonds have become acceptable gems.^[120][121] The change was mostly due to the numbers: the Argyle mine, with its 35,000,000 carats (7,000 kg) of diamonds per year, makes about one-third of global production of natural diamonds;^[122] 80% of Argyle diamonds are brown.^[123]

Industrial diamonds are valued mostly for their hardness and thermal conductivity, making many of the gemological characteristics of diamonds, such as the

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 lower-grade 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.^[126]

Industrial use of diamonds has historically been associated with their hardness, which 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 applications of this property include diamond-tipped drill bits and saws, and the use of diamond powder as an abrasive. Less expensive industrial-grade diamonds (bort) with more flaws and poorer color than gems, are used for such purposes.^[127] 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 compared to alternatives.^[128]

Specialized applications include use in laboratories as containment for

Approximately 130,000,000 carats (26,000 kg) of diamonds are mined annually, with a total value of nearly US$9 billion, and about 100,000 kg (220,000 lb) are synthesized annually.^[130]

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.^[125] 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 concerns over the sale of blood diamonds or conflict diamonds by African paramilitary groups.^[131] 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.

Only a very small fraction of the diamond ore consists of actual diamonds. The ore is crushed, during which care is required not to destroy larger diamonds, 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,^[111] the separation was done with grease belts; diamonds have a stronger tendency to stick to grease than the other minerals in the ore.^[36]

Historically, diamonds were found only in

The Wikibook Development Cooperation Handbook has a page on the topic of: Unsustainable Growth

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.^[131]

In response to public concerns that their diamond purchases were contributing to war and

The Canadian Government has set up a body known as the Canadian Diamond Code of Conduct[144] to help authenticate Canadian diamonds. This is a stringent tracking system of diamonds and helps protect the "conflict free" label of Canadian diamonds.^[145]

Mineral resource exploitation in general causes irreversible environmental damage, which must be weighed against the socio-economic benefits to a country.^[146]

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.^[67] 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.^[147]

The majority of commercially available synthetic diamonds are yellow and are produced by so-called high-pressure high-temperature (

As of 2010, nearly all 5,000 million carats (1,000 tonnes) 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.[147]^[151] Mining companies' expenses average 40 to 60 US dollars per carat for natural colorless diamonds, while synthetic manufacturers' expenses average $2,500 per carat for synthetic, gem-quality colorless diamonds.^[147]: 79 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.^[152]

• 
  Synthetic diamonds of various colors grown by the high-pressure high-temperature technique
• 
  Colorless gem cut from diamond grown by chemical vapor deposition

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.^[153]

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.^[154]

Coatings are increasingly used to give a diamond simulant such as cubic zirconia a more "diamond-like" appearance. One such substance is diamond-like carbon—an amorphous carbonaceous material that has some physical properties similar to those 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. Techniques such as Raman spectroscopy should easily identify such a treatment.^[155]

Early diamond identification tests included a scratch test relying on the superior hardness of diamond. This test is destructive, as a diamond can scratch another diamond, and is rarely used nowadays. Instead, diamond identification relies on its superior thermal conductivity. Electronic thermal probes are widely used in the gemological centers to separate diamonds from their imitations. These probes consist of a pair of battery-powered thermistors mounted in a fine copper tip. One thermistor functions as a heating device while the other measures the temperature of the copper tip: if the stone being tested is a diamond, it will conduct the tip's thermal energy rapidly enough to produce a measurable temperature drop. This test takes about two to three seconds.^[156]

Whereas the thermal probe can separate diamonds from most of their simulants, distinguishing between various types of diamond, for example synthetic or natural, irradiated or non-irradiated, etc., requires more advanced, optical techniques. Those techniques are also used for some diamonds simulants, such as silicon carbide, which pass the thermal conductivity test. Optical techniques can distinguish between natural diamonds and synthetic diamonds. They can also identify the vast majority of treated natural diamonds.^[157] "Perfect" crystals (at the atomic lattice level) have never been found, 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.^[158]

Laboratories use techniques such as spectroscopy, microscopy, and luminescence under shortwave ultraviolet light to determine a diamond's origin.^[157] They also use specially made instruments to aid them in the identification process. Two screening instruments are the DiamondSure and the DiamondView, both produced by the DTC and marketed by the GIA.^[159]

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 Gemmological Institute's^[160] Diamond Spotter. Stones in the D–Z color range can be examined through the DiamondSure UV/visible spectrometer, a tool developed by De Beers.^[158] Similarly, natural diamonds usually have minor imperfections and flaws, such as inclusions of foreign material, that are not seen in synthetic diamonds.

Screening devices based on diamond type detection can be used to make a distinction between diamonds that are certainly natural and diamonds that are potentially synthetic. Those potentially synthetic diamonds require more investigation in a specialized lab. Examples of commercial screening devices are D-Screen (WTOCD / HRD Antwerp), Alpha Diamond Analyzer (Bruker / HRD Antwerp), and D-Secure (DRC Techno).

The name diamond is derived from

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.^[164] Later, in 1797, the English chemist Smithson Tennant repeated and expanded that experiment.^[165] By demonstrating that burning diamond and graphite releases the same amount of gas, he established the chemical equivalence of these substances.^[32]

• Deep carbon cycle
• Diamondoid
• List of diamonds
  • List of largest rough diamonds
• List of minerals
• Superhard material