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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.
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.
There are many theories for its origin, including formation in a star, but no consensus. 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. 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.
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.
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. 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.
Usually, attempting to deform bulk diamond crystal by tension or bending results in brittle fracture. 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.
Boron substitutes for carbon atoms in the diamond lattice, donating a hole into the valence band. Substantial conductivity is commonly observed in nominally undoped diamond grown by chemical vapor deposition.
This conductivity is associated with hydrogen-related species adsorbed at the surface, and it can be removed by annealing or other surface treatments.
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.
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. The structure gradually changes into sp 2 C above this temperature.
Thus, diamonds should be reduced under this temperature. At room temperature, diamonds do not react with any chemical reagents including strong acids and bases.
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. Jewelers must be careful when molding the metal in a diamond ring.
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.
Diamond has a wide bandgap of 5. 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.
Virtually any element can be introduced to diamond by ion implantation. Nitrogen is by far the most common impurity found in gem diamonds and is responsible for the yellow and brown color in diamonds.
Boron is responsible for the blue color. Plastic deformation is the cause of color in some brown  and perhaps pink and red diamonds.
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.
Diamonds of a different color, such as blue, are called fancy colored diamonds and fall under a different grading scale. In , the Wittelsbach Diamond , a 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.
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".
Diamonds are extremely rare, with concentrations of at most parts per billion in source rock. Loose diamonds are also found along existing and ancient shorelines , where they tend to accumulate because of their size and density.
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.
A common misconception is that diamonds are formed 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.
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.
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 ,  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.
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. Fresh rock is dark bluish green to greenish gray, but after exposure rapidly turns brown and crumbles.
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 Ca C O 3. 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. 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.
Finding kimberlites requires persistence, and only a small fraction contain diamonds that are commercially viable.
The only major discoveries since about 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.
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 to argon , or rhenium to osmium.
Those found in kimberlites have ages ranging from 1 to 3. The kimberlites themselves are much younger. Most of them have ages between tens of millions and 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. 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. 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.
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. They formed in eclogite but are distinguished from diamonds of shallower origin by inclusions of majorite a form of garnet with excess silicon.
Diamond is thermodynamically stable at high pressures and temperatures, with the phase transition from graphite occurring at greater temperatures as the pressure increases.
Thus, the deeper origin of some diamonds may reflect unusual growth environments. In the first known natural samples of a phase of ice called Ice VII were found as inclusions in diamond samples.
The mantle has roughly one billion gigatonnes of carbon for comparison, the atmosphere-ocean system has about 44, gigatonnes.
It can also be altered by surface processes like photosynthesis. 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.
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.
Diamonds form from this fluid either by reduction of oxidized carbon e. 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.
Geological evidence supports a model in which kimberlite magma rose 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. 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.
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.
High pressure experiments predict that large quantities of diamonds condense from methane into a "diamond rain" on the ice giant planets Uranus and Neptune.
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.
The most familiar uses of diamonds today are as gemstones used for adornment , and as industrial abrasives for cutting hard materials.
The markets for gem-grade and industrial-grade diamonds value diamonds differently. The 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.
A large, flawless diamond is known as a paragon. 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.
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.
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 by the British imperialist Cecil Rhodes.
De Beers is currently the world's largest operator of diamond production facilities mines and distribution channels for gem-quality diamonds.
As a part of reducing its influence, De Beers withdrew from purchasing diamonds on the open market in and ceased, at the end of , purchasing Russian diamonds mined by the largest Russian diamond company Alrosa.
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.
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.
Recently, diamond cutting centers have been established in China, India, Thailand , Namibia and Botswana. The recent expansion of this industry in India, employing low cost labor, has allowed smaller diamonds to be prepared as gems in greater quantities than was previously economically feasible.
Diamonds prepared as gemstones are sold on diamond exchanges called bourses. There are 28 registered diamond bourses in the world. Diamonds can be sold already set in jewelry, or sold unset "loose".
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.
For example, the diamond might be intended for display or for wear, in a ring or a necklace, singled or surrounded by other gems of certain color and shape.
Some of them are special, produced by certain companies, for example, Phoenix , Cushion , Sole Mio diamonds, etc. 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:.
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.
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. And the firm created new markets in countries where no diamond tradition had existed before.
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,  but this was not a concern as De Beers dominated the diamond market throughout the 20th century.
De Beers still advertises diamonds, but the advertising now mostly promotes its own brands, or licensed product lines, rather than completely "generic" diamond products.
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 , and marketing, brown diamonds have become acceptable gems.
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.
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.
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, known as bort, with more flaws and poorer color than gems, are used for such purposes.
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.
The high thermal conductivity of diamond makes it suitable as a heat sink for integrated circuits in electronics. Product selection may have changed due to availability Because of each country's product availability, the selection on this site may not be the same as the one you were previously on.
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