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Diamond

January 26, 2023

This article is about the mineral. For the gemstone, see Diamond (gemstone). For other uses, including the shape ◊, see Diamond (disambiguation).

Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Another solid form of carbon known as graphite is the chemically stable form of carbon at room temperature and pressure, but diamond is metastable and converts to it at a negligible rate under those conditions. Diamond has the highest hardness and thermal conductivity of any natural material, properties that are used in major industrial applications such as cutting and polishing tools. They are also the reason that diamond anvil cells can subject materials to pressures found deep in the Earth.

Diamond
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.
General
CategoryNative minerals
Formula
(repeating unit)		C
IMA symbolDia[1]
Strunz classification1.CB.10a
Dana classification1.3.6.1
Crystal systemCubic
Crystal classHexoctahedral (m3m)
H-M symbol: (4/m 3 2/m)
Space groupFd3m (No. 227)
Structure
Jmol (3D)Interactive image
Identification
Formula mass12.01 g/mol
ColorTypically yellow, brown, or gray to colorless. Less often blue, green, black, translucent white, pink, violet, orange, purple, and red.
Crystal habitOctahedral
TwinningSpinel law common (yielding "macle")
Cleavage111 (perfect in four directions)
FractureIrregular/Uneven
Mohs scale hardness10 (defining mineral)
LusterAdamantine
StreakColorless
DiaphaneityTransparent to subtransparent to translucent
Specific gravity3.52±0.01
Density3.5–3.53 g/cm3 3500–3530 kg/m3
Polish lusterAdamantine
Optical propertiesIsotropic
Refractive index2.418 (at 500 nm)
BirefringenceNone
PleochroismNone
Dispersion0.044
Melting pointPressure dependent
References[2][3]
Main diamond producing countries

Because the arrangement of atoms in diamond is extremely rigid, few types of impurity can contaminate it (two exceptions are boron and nitrogen). Small numbers of defects or impurities (about one per million of lattice atoms) color diamond blue (boron), yellow (nitrogen), brown (defects), green (radiation exposure), purple, pink, orange, or red. Diamond also has a very high refractive index and a relatively high optical dispersion.

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). Imitation diamonds can also be made out of materials such as cubic zirconia and silicon carbide. Natural, synthetic and imitation diamonds are most commonly distinguished using optical techniques or thermal conductivity measurements.

Properties

Main article: Material properties of diamond

Diamond is a solid form of pure carbon with its atoms arranged in a crystal. Solid carbon comes in different forms known as allotropes depending on the type of chemical bond. The two most common allotropes of pure carbon are diamond and graphite. In graphite the bonds are sp2 orbital hybrids and the atoms form in planes, with each bound to three nearest neighbors 120 degrees apart. In diamond they are sp3 and the atoms form tetrahedra with each bound to four nearest neighbors.[4][5] Tetrahedra are rigid, the bonds are strong, and of all known substances diamond has the greatest number of atoms per unit volume, which is why it is both the hardest and the least compressible.[6][7] It also has a high density, ranging from 3150 to 3530 kilograms per cubic metre (over three times the density of water) in natural diamonds and 3520 kg/m3 in pure diamond.[2] In graphite, the bonds between nearest neighbors are even stronger, but the bonds between parallel adjacent planes are weak, so the planes easily slip past each other. Thus, graphite is much softer than diamond. However, the stronger bonds make graphite less flammable.[8]

Diamonds have been adopted for many uses because of the material's exceptional physical characteristics. It has the highest thermal conductivity and the highest sound velocity. It has low adhesion and friction, and its coefficient of thermal expansion is extremely low. Its optical transparency extends from the far infrared to the deep ultraviolet and it has high optical dispersion. It also has high electrical resistance. It is chemically inert, not reacting with most corrosive substances, and has excellent biological compatibility.[9]

Thermodynamics

 
Theoretically predicted phase diagram of carbon

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 GPa at 0 K and 12 GPa at 5000 K (the diamond/graphite/liquid triple point).[10][11] However, the phases have a wide region about this line where they can coexist. At normal temperature and pressure, 20 °C (293 K) and 1 standard atmosphere (0.10 MPa), the stable phase of carbon is graphite, but diamond is metastable and its rate of conversion to graphite is negligible.[7] However, at temperatures above about 4500 K, diamond rapidly converts to graphite. Rapid conversion of graphite to diamond requires pressures well above the equilibrium line: at 2000 K, a pressure of 35 GPa 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.[12] 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.[13]

Research results published in an article in the scientific journal Nature Physics in 2010 suggest that at ultrahigh 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 giants Neptune and Uranus. Both planets 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 as an explanation as to why the geographic and magnetic poles of the two planets are unaligned.[14][15]

Crystal structure

See also: Crystallographic defects in diamond
 
Diamond unit cell, showing the tetrahedral structure

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.[16] The length of each side of the unit cell is denoted by a and is 3.567 angstroms.[17]

The nearest neighbour 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 face-centered cubic lattices with one displaced by 1⁄4 of the diagonal along a cubic cell, or as one lattice with two atoms associated with each lattice point.[17] Viewed from a <1 1 1> crystallographic direction, it is formed of layers stacked in a repeating ABCABC ... pattern. Diamonds can also form an ABAB ... structure, which is known as hexagonal diamond or lonsdaleite, but this is far less common and is formed under different conditions from cubic carbon.[18]

Crystal habit

 
One face of an uncut octahedral diamond, showing trigons (of positive and negative relief) formed by natural chemical etching

Diamonds occur most often as euhedral or rounded octahedra and twinned octahedra known as macles. 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. Diamonds (especially those with rounded crystal faces) are commonly found coated in nyf, an opaque gum-like skin.[19]

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.[20]

Diamonds can also form polycrystalline aggregates. There have been attempts to classify them into groups with names such as boart, ballas, stewartite, and framesite, but there is no widely accepted set of criteria.[20] Carbonado, a type in which the diamond grains were sintered (fused without melting by the application of heat and pressure), is black in color and tougher than single crystal diamond.[21] It has never been observed in a volcanic rock. There are many theories for its origin, including formation in a star, but no consensus.[20][22][23]

Mechanical

Hardness

 
The extreme hardness of diamond in certain orientations makes it useful in materials science, as in this pyramidal diamond embedded in the working surface of a Vickers hardness tester.

Diamond is the hardest known natural material on both the Vickers scale and the Mohs scale. Diamond's great hardness relative to other materials has been known since antiquity, and is the source of its name. This does not mean that it is infinitely hard, indestructible, or unscratchable.[24] Indeed, diamonds can be scratched by other diamonds[25] and worn down over time even by softer materials, such as vinyl phonograph records.[26]

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).[27] 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 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.[28]

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.[29] 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;[30] 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".[31]

Toughness

Somewhat related to hardness is another mechanical property toughness, which is a material's ability to resist breakage from forceful impact. The toughness of natural diamond has been measured as 7.5–10 MPa·m1/2.[32][33] This value is good compared to other ceramic materials, but poor compared to most engineering materials such as engineering alloys, which typically exhibit toughnesses over 100 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, prior to faceting.[34] "Impact toughness" is one of the main indexes to measure the quality of synthetic industrial diamonds.

Yield strength

Diamond has compressive yield strength of 130–140 GPa.[35] This exceptionally high value, along with the hardness and transparency of diamond, are the reasons that diamond anvil cells are the main tool for high pressure experiments.[36] These anvils have reached pressures of 600 GPa.[37] Much higher pressures may be possible with nanocrystalline diamonds.[36][37]

Elasticity and tensile strength

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,[38] with a maximum local tensile stress of ~89 to 98 GPa,[39] very close to the theoretical limit for this material.[40]

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 diamonds, which are excellent electrical insulators. The conductivity and blue color originate from boron impurity. Boron substitutes for carbon atoms in the diamond lattice, donating a hole into the valence band.[41]

Substantial conductivity is commonly observed in nominally undoped diamond grown by chemical vapor deposition. This conductivity is associated with hydrogen-related species adsorbed at the surface, and it can be removed by annealing or other surface treatments.[42][43]

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.[44]

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.[45]

Surface property

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.[46]

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.[47]

Chemical stability

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 ignition point that ranges from 690 °C (1,274 °F) to 840 °C (1,540 °F); smaller crystals tend to burn more easily. It increases in temperature from red to white heat and burns with a pale blue flame, and continues to burn after the source of heat is removed. By contrast, in air the combustion will cease as soon as the heat is removed because the oxygen is diluted with nitrogen. A clear, flawless, transparent diamond is completely converted to carbon dioxide; any impurities will be left as ash.[48] Heat generated from cutting a diamond will not ignite the diamond,[49] and neither will a cigarette lighter,[50] but house fires and blow torches are hot enough. Jewelers must be careful when molding the metal in a diamond ring.[51]

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.[52] Diamond also reacts with fluorine gas above about 700 °C (1,292 °F).

Color

Main article: Diamond color
 
The most famous colored diamond, the Hope Diamond

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[53] and even less for cobalt. Virtually any element can be introduced to diamond by ion implantation.[54]

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.[55] 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[56] and perhaps pink and red diamonds.[57] In order of increasing rarity, yellow diamond is followed by brown, colorless, then by blue, green, black, pink, orange, purple, and red.[34] "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.[34] 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). Yellow diamonds of high color saturation or a different color, such as pink or blue, are called fancy colored diamonds and fall under a different grading scale.[34]

In 2008, the Wittelsbach Diamond, a 35.56-carat (7.112 g) blue diamond once belonging to the King of Spain, fetched over US$24 million at a Christie's auction.[58] In May 2009, a 7.03-carat (1.406 g) 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 (6.97 million euros, or US$9.5 million at the time).[59] That record was, however, beaten the same year: a 5-carat (1.0 g) vivid pink diamond was sold for $10.8 million in Hong Kong on December 1, 2009.[60]

Clarity

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.[61] 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.[62]

Fluorescence

 
Extremely rare purple fluorescent diamonds from the Ellendale L-Channel deposit in Australia

Between 25% to 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.[63] Incandescent lighting will not cause a diamond to fluoresce. Diamonds can fluoresce in a variety of colours 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.

Thermal Conductivity

Diamonds can be identified by their high thermal conductivity (900–2320 W·m−1·K−1).[64] Their high refractive index is also indicative, but other materials have similar refractivity.

Geology

Diamonds are extremely rare, with concentrations of at most parts per billion in source rock.[20] Before the 20th century, most diamonds were found in alluvial deposits. Loose diamonds are also found along existing and ancient shorelines, where they tend to accumulate because of their size and density.[65]: 149  Rarely, they have been found in glacial till (notably in Wisconsin and Indiana), but these deposits are not of commercial quality.[65]: 19  These types of deposit were derived from localized igneous intrusions through weathering and transport by wind or water.[66]

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.[66] Impact-type microdiamonds can be used as an indicator of ancient impact craters.[67] Popigai impact structure in Russia may have the world's largest diamond deposit, estimated at trillions of carats, and formed by an asteroid impact.[68]

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.[69][70]

Surface distribution

 
Geologic provinces of the world. The pink and orange areas are shields and platforms, which together constitute cratons.

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 kimberlites on the oldest part of cratons, the stable cores of continents with typical ages of 2.5 billion years or more.[66][71]: 314  However, there are exceptions. The Argyle diamond mine in Australia, the largest producer of diamonds by weight in the world, is located in a mobile belt, also known as an orogenic belt,[72] a weaker zone surrounding the central craton that has undergone compressional tectonics. Instead of kimberlite, the host rock is lamproite. Lamproites with diamonds that are not economically viable are also found in the United States, India, and Australia.[66] In addition, diamonds in the Wawa belt of the Superior province in Canada and microdiamonds in the island arc of Japan are found in a type of rock called lamprophyre.[66]

Kimberlites can be found in narrow (1 to 4 meters) dikes and sills, and in pipes with diameters that range from about 75 m to 1.5 km. Fresh rock is dark bluish green to greenish gray, but after exposure rapidly turns brown and crumbles.[73] It is hybrid rock with a chaotic mixture of small minerals and rock fragments (clasts) up to the size of watermelons. They are a mixture of xenocrysts and xenoliths (minerals and rocks carried up from the lower crust and mantle), pieces of surface rock, altered minerals such as serpentine, and new minerals that crystallized during the eruption. The texture varies with depth. The composition forms a continuum with carbonatites, but the latter have too much oxygen for carbon to exist in a pure form. Instead, it is locked up in the mineral calcite (CaCO
3).[66]

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.[66]

Exploration

 
Diavik Mine, on an island in Lac de Gras in northern Canada

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.[66]

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 diamonds in the future.[66]

Ages

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.[20][66] 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.[66]

Origin in mantle

 
Eclogite with centimeter-size garnet crystals
 
Red garnet inclusion in a diamond[74]

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.[66]

Host rocks in a mantle keel include harzburgite and lherzolite, two type of peridotite. The most dominant rock type in the upper mantle, peridotite is an igneous rock consisting mostly of the minerals olivine and pyroxene; it is low in silica and high in magnesium. However, diamonds in peridotite rarely survive the trip to the surface.[66] 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.[20]

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.[20]

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.[20][66]

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 km, straddling the upper and lower mantle, and provide evidence for water-rich fluid at these depths.[75][76]

Carbon sources

The mantle has roughly one billion gigatonnes of carbon (for comparison, the atmosphere-ocean system has about 44,000 gigatonnes).[77] Carbon has two stable isotopes, 12C and 13C, in a ratio of approximately 99:1 by mass.[66] 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.[20]

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.[66]

Formation and growth

 
Age zones in a diamond.[74]

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.[20]

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.[66]

Transport to the surface

 
Diagram of a volcanic pipe

Geological evidence supports a model in which kimberlite magma rises at 4–20 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 (over 200 m/s (450 mph)). Then, at lower pressures, the rock is eroded, forming a pipe and producing fragmented rock (breccia). As the eruption wanes, there is pyroclastic phase and then metamorphism and hydration produces serpentinites.[66]

Double diamonds

 
Double diamond discovered in the Ellendale Diamond Field, Western Australia

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.[78] Another one was found in the Ellendale Diamond Field in Western Australia in 2021.[79]

In space

Main article: Extraterrestrial diamonds

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.[80]

High pressure experiments predict that large quantities of diamonds condense from methane into a "diamond rain" on the ice giant planets Uranus and Neptune.[81][82][83] Some extrasolar planets may be almost entirely composed of diamond.[84]

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.[85][86] Diamonds formed in stars may have been the first minerals.[87]

Industry

See also: Diamonds as an investment, List of countries by diamond production, and Clean Diamond Trade Act
 
A round brilliant cut diamond set in a ring

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.

Gem-grade diamonds

Main article: Diamond (gemstone)

The dispersion of white light into spectral colors is the primary gemological characteristic of gem diamonds. In the 20th century, experts in gemology 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 its mass in carats (a carat being equal to 0.2 grams), cut (quality of the cut is graded according to proportions, symmetry and polish), color (how close to white or colorless; for fancy diamonds how intense is its hue), and clarity (how free is it from inclusions). A large, flawless diamond is known as a paragon.[88]

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 (e.g. pawnbroking, auctions, second-hand jewelry 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; in 2003, 92% of the world's diamonds were cut and polished in Surat, India.[89] 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. 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 mine that can produce between 12,500,000 and 15,000,000 carats (2,500 and 3,000 kg) of diamonds per year[90]). Secondary alluvial diamond deposits, on the other hand, tend to be fragmented amongst many different operators because they can be dispersed over many hundreds of square kilometers (e.g., alluvial deposits in Brazil).[citation needed]

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.[91] This makes Antwerp a de facto "world diamond capital".[92] The city of Antwerp also hosts the Antwerpsche Diamantkring, created in 1929 to become the first and biggest diamond bourse dedicated to rough diamonds.[93] Another important diamond center is New York City, where almost 80% of the world's diamonds are sold, including auction sales.[91]

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 (mines) and distribution channels for gem-quality diamonds. The Diamond Trading Company (DTC) is a subsidiary of De Beers and markets rough diamonds from De Beers-operated mines. De Beers and its subsidiaries own mines that produce some 40% of annual world diamond production. For most of the 20th century over 80% of the world's rough diamonds passed through De Beers,[94] but by 2001–2009 the figure had decreased to around 45%,[95] and by 2013 the company's market share had further decreased to around 38% in value terms and even less by volume.[96] De Beers sold off the vast majority of its diamond stockpile in the late 1990s – early 2000s[97] and the remainder largely represents working stock (diamonds that are being sorted before sale).[98] This was well documented in the press[99] but remains little known to the general public.

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.[100] As of January 2011, De Beers states that it only sells diamonds from the following four countries: Botswana, Namibia, South Africa and Canada.[101] Alrosa had to suspend their sales in October 2008 due to the global energy crisis,[102] but the company reported that it had resumed selling rough diamonds on the open market by October 2009.[103] Apart from Alrosa, other important diamond mining companies include BHP, which is the world's largest mining company;[104] Rio Tinto, the owner of the Argyle (100%), Diavik (60%), and Murowa (78%) diamond mines;[105] and Petra Diamonds, the owner of several major diamond mines in Africa.

 
Diamond polisher in Amsterdam

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 centers such as Tel Aviv, Antwerp, Johannesburg and other cities across the US, Europe and Asia.[34] 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 include sponsoring the World Diamond Congress every two years, as well as the establishment of the International Diamond Council (IDC) to oversee diamond grading.[106]

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).[107] The cutting and polishing of rough diamonds is a specialized skill that is concentrated in a limited number of locations worldwide.[107] 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.[107] 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.[91]

Diamonds prepared as gemstones are sold on diamond exchanges called bourses. There are 28 registered diamond bourses in the world.[108] 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.[109]

Cutting

Main articles: Diamond cutting and Diamond cut
 
The Daria-i-Noor Diamond—an example of unusual diamond cut and jewelry arrangement.

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%.[110] 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.[111] Some of them may be considered as classical, such as round, pear, marquise, oval, hearts and arrows diamonds, etc. Some of them are special, produced by certain companies, for example, Phoenix, Cushion, Sole Mio diamonds, etc.[112]

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.
  • The diamond can be split by a single, well calculated blow of a hammer to a pointed tool, which is quick, but risky. Alternatively, it can be cut with a diamond saw, which is a more reliable but tedious procedure.[111][113]

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.[114] 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.[29]

Marketing

 
Diamond Balance Scale 0.01 - 25 Carat Jewelers Measuring Tool

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

N. W. Ayer & Son, the advertising firm retained by De Beers in the mid-20th century, succeeded in reviving the American diamond market and the firm created new markets in countries where no diamond tradition had existed before. N. W. Ayer's marketing included product placement, advertising focused on the diamond product itself rather than the De Beers brand, and associations with celebrities and royalty. Without advertising the De Beers brand, De Beers was advertising its competitors' diamond products as well,[115] but this was not a concern as De Beers dominated the diamond market throughout the 20th century. De Beers' market share dipped temporarily to second place in the global market below Alrosa in the aftermath of the global economic crisis of 2008, down to less than 29% in terms of carats mined, rather than sold.[116] The campaign lasted for decades but was effectively discontinued by early 2011. De Beers still advertises diamonds, but the advertising now mostly promotes its own brands, or licensed product lines, rather than completely "generic" diamond products.[116] The campaign was perhaps best captured by the slogan "a diamond is forever".[117] This slogan is now being used by De Beers Diamond Jewelers,[118] a jewelry firm which is a 50/50% joint venture between the De Beers mining company and LVMH, the luxury goods conglomerate.

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.[119][120] 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;[121] 80% of Argyle diamonds are brown.[122]

Industrial-grade diamonds

 
A scalpel with synthetic diamond blade
 
Close-up photograph of an angle grinder blade with tiny diamonds shown embedded in the metal
 
A diamond knife blade used for cutting ultrathin sections (typically 70 to 350 nm) for transmission electron microscopy

Industrial diamonds are valued mostly for their hardness and thermal conductivity, making many of the gemological characteristics of diamonds, such as the 4 Cs, irrelevant for most applications. Eighty percent of mined diamonds (equal to about 135,000,000 carats (27,000 kg) annually) are unsuitable for use as gemstones and are used industrially.[123] In addition to mined diamonds, synthetic diamonds found industrial applications almost immediately after their invention in the 1950s; in 2014, 4,500,000,000 carats (900,000 kg) of synthetic diamonds were produced, 90% of which were produced in China. Approximately 90% of diamond grinding grit is currently of synthetic origin.[124]

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.[125]

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.[126] 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.[127]

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.[125] With the continuing advances being made in the production of synthetic diamonds, future applications are becoming feasible. The high thermal conductivity of diamond makes it suitable as a heat sink for integrated circuits in electronics.[128]

Mining

See also: List of diamond mines and Exploration diamond drilling

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.[129]

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.[124] 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.[130] 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,[110] the separation was done with grease belts; diamonds have a stronger tendency to stick to grease than the other minerals in the ore.[34]

 
Siberia's Udachnaya diamond mine

Historically, diamonds were found only in alluvial deposits in Guntur and Krishna district of the Krishna River delta in Southern India.[131] India led the world in diamond production from the time of their discovery in approximately the 9th century BC[132][133] 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.[132] Currently, one of the most prominent Indian mines is located at Panna.[134]

Diamond extraction from primary deposits (kimberlites and lamproites) started in the 1870s after the discovery of the Diamond Fields in South Africa.[135] Production has increased over time and now an accumulated total of 4,500,000,000 carats (900,000 kg) have been mined since that date.[136] Twenty percent of that amount has been mined in the last five years, and during the last 10 years, nine new mines have started production; four more are waiting to be opened soon. Most of these mines are located in Canada, Zimbabwe, Angola, and one in Russia.[136]

In the U.S., diamonds have been found in Arkansas, Colorado, New Mexico, Wyoming, and Montana.[137][138] In 2004, the discovery of a microscopic diamond in the U.S. led to the January 2008 bulk-sampling of kimberlite pipes in a remote part of Montana. The Crater of Diamonds State Park in Arkansas is open to the public, and is the only mine in the world where members of the public can dig for diamonds.[138]

Today, most commercially viable diamond deposits are in Russia (mostly in Sakha Republic, for example Mir pipe and Udachnaya pipe), Botswana, Australia (Northern and Western Australia) and the Democratic Republic of the Congo.[139] In 2005, Russia produced almost one-fifth of the global diamond output, according to the British Geological Survey. Australia boasts the richest diamantiferous pipe, with production from the Argyle diamond mine reaching peak levels of 42 metric tons per year in the 1990s.[137][140] There are also commercial deposits being actively mined in the Northwest Territories of Canada and Brazil.[124] Diamond prospectors continue to search the globe for diamond-bearing kimberlite and lamproite pipes.

Political issues

Main articles: Kimberley Process, Blood diamond, and Child labour in the diamond industry
Unsustainable diamond mining in Sierra Leone

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.[130]

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.[141] 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 2–3% of all diamonds traded.[142] 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".[141]

The Canadian Government has set up a body known as the Canadian Diamond Code of Conduct[143] to help authenticate Canadian diamonds. This is a stringent tracking system of diamonds and helps protect the "conflict free" label of Canadian diamonds.[144]

Mineral resource exploitation in general causes irreversible environmental damage, which must be weighed against the socio-economic benefits to a country.[145]

Synthetics, simulants, and enhancements

Synthetics

Main article: Synthetic diamond

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.[65] 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.[146]

The majority of commercially available synthetic diamonds are yellow and are produced by so-called high-pressure high-temperature (HPHT) processes.[147] 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.[148]

Another popular method of growing synthetic diamond is chemical vapor deposition (CVD). The growth occurs under low pressure (below atmospheric pressure). It involves feeding a mixture of gases (typically 1 to 99 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.[149] This method is mostly used for coatings, but can also produce single crystals several millimeters in size (see picture).[129]

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.[146][150] 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.[146]: 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.[151]

  •  

    Synthetic diamonds of various colors grown by the high-pressure high-temperature technique

  •  

    Colorless gem cut from diamond grown by chemical vapor deposition

Simulants

Main article: Diamond simulant
 
Gem-cut synthetic silicon carbide set in a ring

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.[152]

Enhancements

Main article: Diamond enhancement

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.[153]

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.[154]

Identification

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.[155]

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.[156] "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.[157]

Laboratories use techniques such as spectroscopy, microscopy, and luminescence under shortwave ultraviolet light to determine a diamond's origin.[156] 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.[158]

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[159] Diamond Spotter. Stones in the D-Z color range can be examined through the DiamondSure UV/visible spectrometer, a tool developed by De Beers.[157] 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).

Etymology, earliest use and composition discovery

The name diamond is derived from Ancient Greek: ἀδάμας (adámas), 'proper, unalterable, unbreakable, untamed', from ἀ- (a-), 'not' + Ancient Greek: δαμάω (damáō), 'to overpower, tame'.[160] 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.[132]

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.[161][162] 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.[117]

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.[163] Later in 1797, the English chemist Smithson Tennant repeated and expanded that experiment.[164] By demonstrating that burning diamond and graphite releases the same amount of gas, he established the chemical equivalence of these substances.[30]

See also

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General and cited references

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  • Zaitsev AM (2001). Optical Properties of Diamond: A Data Handbook. Springer. ISBN 978-3-540-66582-3.

Further reading

  • Epstein EJ (February 1982). . The Atlantic Monthly. Archived from the original on 15 March 2006. Retrieved 2 January 2023.
  • Tyson P (November 2000). "Diamonds in the Sky". The Diamond Deception. Nova. PBS. Retrieved 2 January 2023.

External links

  • Properties of diamond: Ioffe database
  • at the Wayback Machine (archived 2017-09-08) (2007) Gemological Institute of America (GIA)

January 26, 2023
diamond, this, article, about, mineral, gemstone, gemstone, other, uses, including, shape, disambiguation, solid, form, element, carbon, with, atoms, arranged, crystal, structure, called, diamond, cubic, another, solid, form, carbon, known, graphite, chemicall. This article is about the mineral For the gemstone see Diamond gemstone For other uses including the shape see Diamond disambiguation Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic Another solid form of carbon known as graphite is the chemically stable form of carbon at room temperature and pressure but diamond is metastable and converts to it at a negligible rate under those conditions Diamond has the highest hardness and thermal conductivity of any natural material properties that are used in major industrial applications such as cutting and polishing tools They are also the reason that diamond anvil cells can subject materials to pressures found deep in the Earth DiamondThe 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 GeneralCategoryNative mineralsFormula repeating unit CIMA symbolDia 1 Strunz classification1 CB 10aDana classification1 3 6 1Crystal systemCubicCrystal classHexoctahedral m3 m H M symbol 4 m 3 2 m Space groupFd3 m No 227 StructureJmol 3D Interactive imageIdentificationFormula mass12 01 g molColorTypically yellow brown or gray to colorless Less often blue green black translucent white pink violet orange purple and red Crystal habitOctahedralTwinningSpinel law common yielding macle Cleavage111 perfect in four directions FractureIrregular UnevenMohs scale hardness10 defining mineral LusterAdamantineStreakColorlessDiaphaneityTransparent to subtransparent to translucentSpecific gravity3 52 0 01Density3 5 3 53 g cm3 3500 3530 kg m3Polish lusterAdamantineOptical propertiesIsotropicRefractive index2 418 at 500 nm BirefringenceNonePleochroismNoneDispersion0 044Melting pointPressure dependentReferences 2 3 Main diamond producing countries Because the arrangement of atoms in diamond is extremely rigid few types of impurity can contaminate it two exceptions are boron and nitrogen Small numbers of defects or impurities about one per million of lattice atoms color diamond blue boron yellow nitrogen brown defects green radiation exposure purple pink orange or red Diamond also has a very high refractive index and a relatively high optical dispersion 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 Imitation diamonds can also be made out of materials such as cubic zirconia and silicon carbide Natural synthetic and imitation diamonds are most commonly distinguished using optical techniques or thermal conductivity measurements Contents 1 Properties 1 1 Thermodynamics 1 2 Crystal structure 1 3 Crystal habit 1 4 Mechanical 1 4 1 Hardness 1 4 2 Toughness 1 4 3 Yield strength 1 4 4 Elasticity and tensile strength 1 5 Electrical conductivity 1 6 Surface property 1 7 Chemical stability 1 8 Color 1 9 Clarity 1 10 Fluorescence 1 11 Thermal Conductivity 2 Geology 2 1 Surface distribution 2 2 Exploration 2 3 Ages 2 4 Origin in mantle 2 5 Carbon sources 2 6 Formation and growth 2 7 Transport to the surface 2 8 Double diamonds 2 9 In space 3 Industry 3 1 Gem grade diamonds 3 1 1 Cutting 3 1 2 Marketing 3 2 Industrial grade diamonds 3 3 Mining 3 3 1 Political issues 4 Synthetics simulants and enhancements 4 1 Synthetics 4 2 Simulants 4 3 Enhancements 4 4 Identification 5 Etymology earliest use and composition discovery 6 See also 7 Citations 8 General and cited references 9 Further reading 10 External linksPropertiesMain article Material properties of diamond Diamond is a solid form of pure carbon with its atoms arranged in a crystal Solid carbon comes in different forms known as allotropes depending on the type of chemical bond The two most common allotropes of pure carbon are diamond and graphite In graphite the bonds are sp2 orbital hybrids and the atoms form in planes with each bound to three nearest neighbors 120 degrees apart In diamond they are sp3 and the atoms form tetrahedra with each bound to four nearest neighbors 4 5 Tetrahedra are rigid the bonds are strong and of all known substances diamond has the greatest number of atoms per unit volume which is why it is both the hardest and the least compressible 6 7 It also has a high density ranging from 3150 to 3530 kilograms per cubic metre over three times the density of water in natural diamonds and 3520 kg m3 in pure diamond 2 In graphite the bonds between nearest neighbors are even stronger but the bonds between parallel adjacent planes are weak so the planes easily slip past each other Thus graphite is much softer than diamond However the stronger bonds make graphite less flammable 8 Diamonds have been adopted for many uses because of the material s exceptional physical characteristics It has the highest thermal conductivity and the highest sound velocity It has low adhesion and friction and its coefficient of thermal expansion is extremely low Its optical transparency extends from the far infrared to the deep ultraviolet and it has high optical dispersion It also has high electrical resistance It is chemically inert not reacting with most corrosive substances and has excellent biological compatibility 9 Thermodynamics Theoretically predicted phase diagram of carbon 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 GPa at 0 K and 12 GPa at 5000 K the diamond graphite liquid triple point 10 11 However the phases have a wide region about this line where they can coexist At normal temperature and pressure 20 C 293 K and 1 standard atmosphere 0 10 MPa the stable phase of carbon is graphite but diamond is metastable and its rate of conversion to graphite is negligible 7 However at temperatures above about 4500 K diamond rapidly converts to graphite Rapid conversion of graphite to diamond requires pressures well above the equilibrium line at 2000 K a pressure of 35 GPa 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 12 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 13 Research results published in an article in the scientific journal Nature Physics in 2010 suggest that at ultrahigh 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 giants Neptune and Uranus Both planets 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 as an explanation as to why the geographic and magnetic poles of the two planets are unaligned 14 15 Crystal structure See also Crystallographic defects in diamond Diamond unit cell showing the tetrahedral structure 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 16 The length of each side of the unit cell is denoted by a and is 3 567 angstroms 17 The nearest neighbour distance in the diamond lattice is 1 732a 4 where a is the lattice constant usually given in Angstroms as a 3 567 A which is 0 3567 nm A diamond cubic lattice can be thought of as two interpenetrating face centered cubic lattices with one displaced by 1 4 of the diagonal along a cubic cell or as one lattice with two atoms associated with each lattice point 17 Viewed from a lt 1 1 1 gt crystallographic direction it is formed of layers stacked in a repeating ABCABC pattern Diamonds can also form an ABAB structure which is known as hexagonal diamond or lonsdaleite but this is far less common and is formed under different conditions from cubic carbon 18 Crystal habit One face of an uncut octahedral diamond showing trigons of positive and negative relief formed by natural chemical etching Diamonds occur most often as euhedral or rounded octahedra and twinned octahedra known as macles 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 Diamonds especially those with rounded crystal faces are commonly found coated in nyf an opaque gum like skin 19 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 20 Diamonds can also form polycrystalline aggregates There have been attempts to classify them into groups with names such as boart ballas stewartite and framesite but there is no widely accepted set of criteria 20 Carbonado a type in which the diamond grains were sintered fused without melting by the application of heat and pressure is black in color and tougher than single crystal diamond 21 It has never been observed in a volcanic rock There are many theories for its origin including formation in a star but no consensus 20 22 23 Mechanical Hardness The extreme hardness of diamond in certain orientations makes it useful in materials science as in this pyramidal diamond embedded in the working surface of a Vickers hardness tester Diamond is the hardest known natural material on both the Vickers scale and the Mohs scale Diamond s great hardness relative to other materials has been known since antiquity and is the source of its name This does not mean that it is infinitely hard indestructible or unscratchable 24 Indeed diamonds can be scratched by other diamonds 25 and worn down over time even by softer materials such as vinyl phonograph records 26 Diamond hardness depends on its purity crystalline perfection and orientation hardness is higher for flawless pure crystals oriented to the lt 111 gt direction along the longest diagonal of the cubic diamond lattice 27 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 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 28 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 29 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 30 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 31 Toughness Somewhat related to hardness is another mechanical property toughness which is a material s ability to resist breakage from forceful impact The toughness of natural diamond has been measured as 7 5 10 MPa m1 2 32 33 This value is good compared to other ceramic materials but poor compared to most engineering materials such as engineering alloys which typically exhibit toughnesses over 100 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 prior to faceting 34 Impact toughness is one of the main indexes to measure the quality of synthetic industrial diamonds Yield strength Diamond has compressive yield strength of 130 140 GPa 35 This exceptionally high value along with the hardness and transparency of diamond are the reasons that diamond anvil cells are the main tool for high pressure experiments 36 These anvils have reached pressures of 600 GPa 37 Much higher pressures may be possible with nanocrystalline diamonds 36 37 Elasticity and tensile strength 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 38 with a maximum local tensile stress of 89 to 98 GPa 39 very close to the theoretical limit for this material 40 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 diamonds which are excellent electrical insulators The conductivity and blue color originate from boron impurity Boron substitutes for carbon atoms in the diamond lattice donating a hole into the valence band 41 Substantial conductivity is commonly observed in nominally undoped diamond grown by chemical vapor deposition This conductivity is associated with hydrogen related species adsorbed at the surface and it can be removed by annealing or other surface treatments 42 43 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 44 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 45 Surface property 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 46 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 47 Chemical stability 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 ignition point that ranges from 690 C 1 274 F to 840 C 1 540 F smaller crystals tend to burn more easily It increases in temperature from red to white heat and burns with a pale blue flame and continues to burn after the source of heat is removed By contrast in air the combustion will cease as soon as the heat is removed because the oxygen is diluted with nitrogen A clear flawless transparent diamond is completely converted to carbon dioxide any impurities will be left as ash 48 Heat generated from cutting a diamond will not ignite the diamond 49 and neither will a cigarette lighter 50 but house fires and blow torches are hot enough Jewelers must be careful when molding the metal in a diamond ring 51 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 52 Diamond also reacts with fluorine gas above about 700 C 1 292 F Color Main article Diamond color Brown diamonds at the National Museum of Natural History in Washington D C The most famous colored diamond the Hope Diamond 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 53 and even less for cobalt Virtually any element can be introduced to diamond by ion implantation 54 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 55 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 56 and perhaps pink and red diamonds 57 In order of increasing rarity yellow diamond is followed by brown colorless then by blue green black pink orange purple and red 34 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 34 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 Yellow diamonds of high color saturation or a different color such as pink or blue are called fancy colored diamonds and fall under a different grading scale 34 In 2008 the Wittelsbach Diamond a 35 56 carat 7 112 g blue diamond once belonging to the King of Spain fetched over US 24 million at a Christie s auction 58 In May 2009 a 7 03 carat 1 406 g 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 6 97 million euros or US 9 5 million at the time 59 That record was however beaten the same year a 5 carat 1 0 g vivid pink diamond was sold for 10 8 million in Hong Kong on December 1 2009 60 Clarity 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 61 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 62 Fluorescence Extremely rare purple fluorescent diamonds from the Ellendale L Channel deposit in Australia Between 25 to 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 63 Incandescent lighting will not cause a diamond to fluoresce Diamonds can fluoresce in a variety of colours 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 Thermal Conductivity Diamonds can be identified by their high thermal conductivity 900 2320 W m 1 K 1 64 Their high refractive index is also indicative but other materials have similar refractivity GeologyDiamonds are extremely rare with concentrations of at most parts per billion in source rock 20 Before the 20th century most diamonds were found in alluvial deposits Loose diamonds are also found along existing and ancient shorelines where they tend to accumulate because of their size and density 65 149 Rarely they have been found in glacial till notably in Wisconsin and Indiana but these deposits are not of commercial quality 65 19 These types of deposit were derived from localized igneous intrusions through weathering and transport by wind or water 66 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 66 Impact type microdiamonds can be used as an indicator of ancient impact craters 67 Popigai impact structure in Russia may have the world s largest diamond deposit estimated at trillions of carats and formed by an asteroid impact 68 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 69 70 Surface distribution Geologic provinces of the world The pink and orange areas are shields and platforms which together constitute cratons 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 kimberlites on the oldest part of cratons the stable cores of continents with typical ages of 2 5 billion years or more 66 71 314 However there are exceptions The Argyle diamond mine in Australia the largest producer of diamonds by weight in the world is located in a mobile belt also known as an orogenic belt 72 a weaker zone surrounding the central craton that has undergone compressional tectonics Instead of kimberlite the host rock is lamproite Lamproites with diamonds that are not economically viable are also found in the United States India and Australia 66 In addition diamonds in the Wawa belt of the Superior province in Canada and microdiamonds in the island arc of Japan are found in a type of rock called lamprophyre 66 Kimberlites can be found in narrow 1 to 4 meters dikes and sills and in pipes with diameters that range from about 75 m to 1 5 km Fresh rock is dark bluish green to greenish gray but after exposure rapidly turns brown and crumbles 73 It is hybrid rock with a chaotic mixture of small minerals and rock fragments clasts up to the size of watermelons They are a mixture of xenocrysts and xenoliths minerals and rocks carried up from the lower crust and mantle pieces of surface rock altered minerals such as serpentine and new minerals that crystallized during the eruption The texture varies with depth The composition forms a continuum with carbonatites but the latter have too much oxygen for carbon to exist in a pure form Instead it is locked up in the mineral calcite CaCO3 66 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 66 Exploration Diavik Mine on an island in Lac de Gras in northern Canada 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 66 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 diamonds in the future 66 Ages 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 20 66 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 66 Origin in mantle Eclogite with centimeter size garnet crystals Red garnet inclusion in a diamond 74 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 66 Host rocks in a mantle keel include harzburgite and lherzolite two type of peridotite The most dominant rock type in the upper mantle peridotite is an igneous rock consisting mostly of the minerals olivine and pyroxene it is low in silica and high in magnesium However diamonds in peridotite rarely survive the trip to the surface 66 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 20 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 20 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 20 66 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 km straddling the upper and lower mantle and provide evidence for water rich fluid at these depths 75 76 Carbon sources The mantle has roughly one billion gigatonnes of carbon for comparison the atmosphere ocean system has about 44 000 gigatonnes 77 Carbon has two stable isotopes 12C and 13C in a ratio of approximately 99 1 by mass 66 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 d13C 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 20 Populations of diamonds from different sources have distributions of d13C 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 66 Formation and growth Age zones in a diamond 74 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 20 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 66 Transport to the surface Diagram of a volcanic pipe Geological evidence supports a model in which kimberlite magma rises at 4 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 over 200 m s 450 mph Then at lower pressures the rock is eroded forming a pipe and producing fragmented rock breccia As the eruption wanes there is pyroclastic phase and then metamorphism and hydration produces serpentinites 66 Double diamonds Double diamond discovered in the Ellendale Diamond Field Western Australia 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 78 Another one was found in the Ellendale Diamond Field in Western Australia in 2021 79 In space Main article Extraterrestrial diamonds 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 80 High pressure experiments predict that large quantities of diamonds condense from methane into a diamond rain on the ice giant planets Uranus and Neptune 81 82 83 Some extrasolar planets may be almost entirely composed of diamond 84 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 85 86 Diamonds formed in stars may have been the first minerals 87 IndustrySee also Diamonds as an investment List of countries by diamond production and Clean Diamond Trade Act A round brilliant cut diamond set in a ring 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 Gem grade diamonds Main article Diamond gemstone The dispersion of white light into spectral colors is the primary gemological characteristic of gem diamonds In the 20th century experts in gemology 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 its mass in carats a carat being equal to 0 2 grams cut quality of the cut is graded according to proportions symmetry and polish color how close to white or colorless for fancy diamonds how intense is its hue and clarity how free is it from inclusions A large flawless diamond is known as a paragon 88 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 e g pawnbroking auctions second hand jewelry 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 in 2003 92 of the world s diamonds were cut and polished in Surat India 89 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 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 mine that can produce between 12 500 000 and 15 000 000 carats 2 500 and 3 000 kg of diamonds per year 90 Secondary alluvial diamond deposits on the other hand tend to be fragmented amongst many different operators because they can be dispersed over many hundreds of square kilometers e g alluvial deposits in Brazil citation needed 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 91 This makes Antwerp a de facto world diamond capital 92 The city of Antwerp also hosts the Antwerpsche Diamantkring created in 1929 to become the first and biggest diamond bourse dedicated to rough diamonds 93 Another important diamond center is New York City where almost 80 of the world s diamonds are sold including auction sales 91 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 mines and distribution channels for gem quality diamonds The Diamond Trading Company DTC is a subsidiary of De Beers and markets rough diamonds from De Beers operated mines De Beers and its subsidiaries own mines that produce some 40 of annual world diamond production For most of the 20th century over 80 of the world s rough diamonds passed through De Beers 94 but by 2001 2009 the figure had decreased to around 45 95 and by 2013 the company s market share had further decreased to around 38 in value terms and even less by volume 96 De Beers sold off the vast majority of its diamond stockpile in the late 1990s early 2000s 97 and the remainder largely represents working stock diamonds that are being sorted before sale 98 This was well documented in the press 99 but remains little known to the general public 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 100 As of January 2011 De Beers states that it only sells diamonds from the following four countries Botswana Namibia South Africa and Canada 101 Alrosa had to suspend their sales in October 2008 due to the global energy crisis 102 but the company reported that it had resumed selling rough diamonds on the open market by October 2009 103 Apart from Alrosa other important diamond mining companies include BHP which is the world s largest mining company 104 Rio Tinto the owner of the Argyle 100 Diavik 60 and Murowa 78 diamond mines 105 and Petra Diamonds the owner of several major diamond mines in Africa Diamond polisher in Amsterdam 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 centers such as Tel Aviv Antwerp Johannesburg and other cities across the US Europe and Asia 34 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 include sponsoring the World Diamond Congress every two years as well as the establishment of the International Diamond Council IDC to oversee diamond grading 106 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 107 The cutting and polishing of rough diamonds is a specialized skill that is concentrated in a limited number of locations worldwide 107 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 107 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 91 Diamonds prepared as gemstones are sold on diamond exchanges called bourses There are 28 registered diamond bourses in the world 108 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 109 Cutting Main articles Diamond cutting and Diamond cut The Daria i Noor Diamond an example of unusual diamond cut and jewelry arrangement 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 50 110 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 111 Some of them may be considered as classical such as round pear marquise oval hearts and arrows diamonds etc Some of them are special produced by certain companies for example Phoenix Cushion Sole Mio diamonds etc 112 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 The diamond can be split by a single well calculated blow of a hammer to a pointed tool which is quick but risky Alternatively it can be cut with a diamond saw which is a more reliable but tedious procedure 111 113 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 114 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 29 Marketing Diamond Balance Scale 0 01 25 Carat Jewelers Measuring Tool Marketing has significantly affected the image of diamond as a valuable commodity N W Ayer amp Son the advertising firm retained by De Beers in the mid 20th century succeeded in reviving the American diamond market and the firm created new markets in countries where no diamond tradition had existed before N W Ayer s marketing included product placement advertising focused on the diamond product itself rather than the De Beers brand and associations with celebrities and royalty Without advertising the De Beers brand De Beers was advertising its competitors diamond products as well 115 but this was not a concern as De Beers dominated the diamond market throughout the 20th century De Beers market share dipped temporarily to second place in the global market below Alrosa in the aftermath of the global economic crisis of 2008 down to less than 29 in terms of carats mined rather than sold 116 The campaign lasted for decades but was effectively discontinued by early 2011 De Beers still advertises diamonds but the advertising now mostly promotes its own brands or licensed product lines rather than completely generic diamond products 116 The campaign was perhaps best captured by the slogan a diamond is forever 117 This slogan is now being used by De Beers Diamond Jewelers 118 a jewelry firm which is a 50 50 joint venture between the De Beers mining company and LVMH the luxury goods conglomerate 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 119 120 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 121 80 of Argyle diamonds are brown 122 Industrial grade diamonds A scalpel with synthetic diamond blade Close up photograph of an angle grinder blade with tiny diamonds shown embedded in the metal A diamond knife blade used for cutting ultrathin sections typically 70 to 350 nm for transmission electron microscopy Industrial diamonds are valued mostly for their hardness and thermal conductivity making many of the gemological characteristics of diamonds such as the 4 Cs irrelevant for most applications Eighty percent of mined diamonds equal to about 135 000 000 carats 27 000 kg annually are unsuitable for use as gemstones and are used industrially 123 In addition to mined diamonds synthetic diamonds found industrial applications almost immediately after their invention in the 1950s in 2014 4 500 000 000 carats 900 000 kg of synthetic diamonds were produced 90 of which were produced in China Approximately 90 of diamond grinding grit is currently of synthetic origin 124 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 125 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 126 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 127 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 125 With the continuing advances being made in the production of synthetic diamonds future applications are becoming feasible The high thermal conductivity of diamond makes it suitable as a heat sink for integrated circuits in electronics 128 Mining See also List of diamond mines and Exploration diamond drilling 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 129 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 124 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 130 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 110 the separation was done with grease belts diamonds have a stronger tendency to stick to grease than the other minerals in the ore 34 Siberia s Udachnaya diamond mine Historically diamonds were found only in alluvial deposits in Guntur and Krishna district of the Krishna River delta in Southern India 131 India led the world in diamond production from the time of their discovery in approximately the 9th century BC 132 133 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 132 Currently one of the most prominent Indian mines is located at Panna 134 Diamond extraction from primary deposits kimberlites and lamproites started in the 1870s after the discovery of the Diamond Fields in South Africa 135 Production has increased over time and now an accumulated total of 4 500 000 000 carats 900 000 kg have been mined since that date 136 Twenty percent of that amount has been mined in the last five years and during the last 10 years nine new mines have started production four more are waiting to be opened soon Most of these mines are located in Canada Zimbabwe Angola and one in Russia 136 In the U S diamonds have been found in Arkansas Colorado New Mexico Wyoming and Montana 137 138 In 2004 the discovery of a microscopic diamond in the U S led to the January 2008 bulk sampling of kimberlite pipes in a remote part of Montana The Crater of Diamonds State Park in Arkansas is open to the public and is the only mine in the world where members of the public can dig for diamonds 138 Today most commercially viable diamond deposits are in Russia mostly in Sakha Republic for example Mir pipe and Udachnaya pipe Botswana Australia Northern and Western Australia and the Democratic Republic of the Congo 139 In 2005 Russia produced almost one fifth of the global diamond output according to the British Geological Survey Australia boasts the richest diamantiferous pipe with production from the Argyle diamond mine reaching peak levels of 42 metric tons per year in the 1990s 137 140 There are also commercial deposits being actively mined in the Northwest Territories of Canada and Brazil 124 Diamond prospectors continue to search the globe for diamond bearing kimberlite and lamproite pipes Political issues Main articles Kimberley Process Blood diamond and Child labour in the diamond industry source source source Unsustainable diamond mining in Sierra Leone 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 130 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 141 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 3 of all diamonds traded 142 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 141 The Canadian Government has set up a body known as the Canadian Diamond Code of Conduct 143 to help authenticate Canadian diamonds This is a stringent tracking system of diamonds and helps protect the conflict free label of Canadian diamonds 144 Mineral resource exploitation in general causes irreversible environmental damage which must be weighed against the socio economic benefits to a country 145 Synthetics simulants and enhancementsSynthetics Main article Synthetic diamond 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 65 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 146 The majority of commercially available synthetic diamonds are yellow and are produced by so called high pressure high temperature HPHT processes 147 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 148 Another popular method of growing synthetic diamond is chemical vapor deposition CVD The growth occurs under low pressure below atmospheric pressure It involves feeding a mixture of gases typically 1 to 99 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 149 This method is mostly used for coatings but can also produce single crystals several millimeters in size see picture 129 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 146 150 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 146 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 151 Synthetic diamonds of various colors grown by the high pressure high temperature technique Colorless gem cut from diamond grown by chemical vapor depositionSimulants Main article Diamond simulant Gem cut synthetic silicon carbide set in a ring 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 152 Enhancements Main article Diamond enhancement 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 153 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 154 Identification 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 155 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 156 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 157 Laboratories use techniques such as spectroscopy microscopy and luminescence under shortwave ultraviolet light to determine a diamond s origin 156 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 158 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 159 Diamond Spotter Stones in the D Z color range can be examined through the DiamondSure UV visible spectrometer a tool developed by De Beers 157 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 Etymology earliest use and composition discoveryThe name diamond is derived from Ancient Greek ἀdamas adamas proper unalterable unbreakable untamed from ἀ a not Ancient Greek damaw damaō to overpower tame 160 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 132 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 161 162 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 117 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 163 Later in 1797 the English chemist Smithson Tennant repeated and expanded that experiment 164 By demonstrating that burning diamond and graphite releases the same amount of gas he established the chemical equivalence of 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cette Academie History of the Royal Academy of Sciences with the Memoirs of Mathematics amp Physics drawn from the records of this academy in French Gallica Academie des sciences pp 564 591 ISSN 1967 4783 ark 12148 bpt6k35711 retrieved 2022 07 01Lavoisier A 2007 10 15 1772 part 2 Second memoire sur la destruction du diamant par le feu Second memoir on the destruction of diamond by fire Histoire de l Academie royale des sciences avec les Memoires de Mathematique amp de Physique tires des registres de cette Academie in French Gallica Academie des sciences pp 591 616 ISSN 1967 4783 ark 12148 bpt6k35711 retrieved 2022 07 01 Smithson T 1797 December 15 1797 On the nature of the diamond Philosophical Transactions of the Royal Society of London Giving Some Account of the Present Undertakings Studies and Labours of the Ingenious in Many Considerable Parts of the World 87 123 127 doi 10 1098 rstl 1797 0005 S2CID 186213726 Retrieved 2022 07 01 General and cited referencesEven Zohar C 2007 From Mine to Mistress Corporate Strategies and Government Policies in the International Diamond Industry 2nd ed Mining Journal Press Davies G 1994 Properties and growth of diamond INSPEC ISBN 978 0 85296 875 8 O Donoghue M 2006 Gems Elsevier ISBN 978 0 7506 5856 0 O Donoghue M Joyner L 2003 Identification of gemstones Great Britain Butterworth Heinemann ISBN 978 0 7506 5512 5 Feldman A Robins LH 1991 Applications of Diamond Films and Related Materials Elsevier ISBN 978 1 48329124 6 Field JE 1979 The Properties of Diamond London Academic Press ISBN 978 0 12 255350 9 Field JE 1992 The Properties of Natural and Synthetic Diamond London Academic Press ISBN 978 0 12 255352 3 Hershey W 1940 The Book of Diamonds Hearthside Press New York ISBN 978 1 4179 7715 4 Koizumi S Nebel CE Nesladek M 2008 Physics and Applications of CVD Diamond Wiley VCH ISBN 978 3 527 40801 6 Pan LS Kani DR 1995 Diamond Electronic Properties and Applications Kluwer Academic Publishers ISBN 978 0 7923 9524 9 Pagel Theisen V 2001 Diamond Grading ABC the Manual Antwerp Rubin amp Son ISBN 978 3 9800434 6 5 Radovic RL Walker RM Thrower PA 1965 Chemistry and physics of carbon a series of advances New York Marcel Dekker ISBN 978 0 8247 0987 7 Tolkowsky M 1919 Diamond Design A Study of the Reflection and Refraction of Light in a Diamond London E amp F N Spon Wise RW 2016 Secrets of the Gem Trade The Connoisseur s Guide to Precious Gemstones Second ed Brunswick House Press ISBN 978 0 9728223 2 9 Zaitsev AM 2001 Optical Properties of Diamond A Data Handbook Springer ISBN 978 3 540 66582 3 Further readingEpstein EJ February 1982 Have You Ever Tried to Sell a Diamond The Atlantic Monthly Archived from the original on 15 March 2006 Retrieved 2 January 2023 Tyson P November 2000 Diamonds in the Sky The Diamond Deception Nova PBS Retrieved 2 January 2023 External linksDiamond at Wikipedia s sister projects Definitions from Wiktionary Media from Commons Quotations from Wikiquote Properties of diamond Ioffe database A Contribution to the Understanding of Blue Fluorescence on the Appearance of Diamonds at the Wayback Machine archived 2017 09 08 2007 Gemological Institute of America GIA Retrieved from https en wikipedia org w index php title Diamond amp oldid 1135657767, wikipedia, wiki, book, books, library,

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