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Diamond is a
solid form of the element carbon
solid form of the element carbon
with its atoms arranged in a
crystal structure In crystallography Crystallography is the experimental science of determining the arrangement of atoms in crystalline solids (see crystal structure). The word "crystallography" is derived from the Greek language, Greek words ''crystallon'' "col ...

crystal structure
called
diamond cubic The diamond cubic crystal structure is a repeating pattern of 8 atoms that certain materials may adopt as they solidify. While the first known example was diamond, other elements in group 14 also adopt this structure, including α-tin, the se ...
. At
room temperature and pressure Colloquially, room temperature is the range of air temperatures that most people prefer for indoor settings, which feel comfortable when wearing typical indoor clothing. Human comfort can extend beyond this range depending on humidity, air circula ...
, another solid form of carbon known as
graphite Graphite (), archaically referred to as plumbago, is a crystalline form of the element carbon Carbon (from la, carbo "coal") is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table ...

graphite
is the chemically stable form of carbon, but diamond converts to it extremely slowly. Diamond has the highest
hardness Hardness (antonym: softness) is a measure of the resistance to localized induced by either mechanical or . In general, different materials differ in their hardness; for example hard metals such as and are harder than soft metals such as and ...
and
thermal conductivity The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k, \lambda, or \kappa. Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal ...

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 cell upright=1.2, Schematics of the core of a diamond anvil cell. The culets (tip) of the two diamond anvils are typically 100–250 microns across. A diamond anvil cell (DAC) is a high-pressure In science Science (from the Latin word ''scientia' ...

diamond anvil cell
s can subject materials to pressures found deep in the Earth. Because the arrangement of atoms in diamond is extremely rigid, few types of impurity can contaminate it (two exceptions are
boron Boron is a chemical element with the Symbol (chemistry), symbol B and atomic number 5. Produced entirely by cosmic ray spallation and supernovae and not by stellar nucleosynthesis, it is a low-abundance element in the Solar System a ...

boron
and
nitrogen Nitrogen is the chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science ...

nitrogen
). Small numbers of
defects A defect is a physical, functional, or aesthetic attribute of a product or service that exhibits that the product or service failed to meet one of the desired specifications. Defect, defects or defected may also refer to: Examples * Angular defect ...
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 In optics, the refractive index (also known as refraction index or index of refraction) of a optical medium, material is a dimensionless number that describes how fast EM radiation, light travels through the material. It is defined as :n = \frac ...

refractive index
and a relatively high
optical dispersion A compact fluorescent lamp seen through an Amici prism ">Amici_prism.html" ;"title="compact fluorescent lamp seen through an Amici prism">compact fluorescent lamp seen through an Amici prism In optics, dispersion is the phenomenon in which the ...

optical dispersion
. Most natural diamonds have ages between 1 billion and 3.5 billion years. Most were formed at depths between in the Earth's mantle, although a few have come from as deep as . 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 eruption Several types of volcanic eruptions—during which lava Lava is magma once it has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or t ...

volcanic eruption
s and deposited in
igneous rock Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main The three types of rocks, rock types, the others being Sedimentary rock, sedimentary and metamorphic rock, metamorphic. Igneous rock is ...
s known as
kimberlite Cross-section of kimberlite from South Africa. The kimberlite matrix is made up of clay minerals and carbonates, presented in blue, purple and buff colours. Kimberlite is an igneous rock, which sometimes contains diamonds. It is named after the ...

kimberlite
s and
lamproite Lamproite is an ultrapotassic mantle-derived volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. Abou ...
s.
Synthetic diamondSynthetic things are composed of multiple parts, often with the implication that they are artificial. In particular, 'synthetic' may refer to: Science * Synthetic chemical or compound, produced by the process of chemical synthesis * Organic compo ...

Synthetic diamond
s can be grown from high-purity carbon under high pressures and temperatures or from
hydrocarbon In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, prop ...
gases by
chemical vapor deposition Chemical vapor deposition (CVD) is a vacuum deposition Vacuum deposition is a family of processes used to deposit layers of material atom-by-atom or molecule-by-molecule on a solid surface. These processes operate at pressures well below atmo ...
(CVD). Imitation diamonds can also be made out of materials such as
cubic zirconia Cubic zirconia (CZ) is the cubic crystalline form of zirconium dioxide Zirconium dioxide (), sometimes known as zirconia (not to be confused with zircon Zircon ( or ) is a mineral In geology Geology (from the Ancient Greek γῆ ...
and
silicon carbide Silicon carbide (SiC), also known as carborundum (), is a semiconductor containing silicon and carbon. It occurs in nature as the extremely rare mineral moissanite. Synthetic SiC powder has been mass-produced since 1893 for use as an abrasive. Gra ...

silicon carbide
. Natural, synthetic and imitation diamonds are most commonly distinguished using optical techniques or thermal conductivity measurements.


Material properties

Diamond is a solid form of pure carbon with its atoms arranged in a crystal. Solid carbon comes in different forms known as
allotrope Allotropy or allotropism () is the property of some chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting o ...
s depending on the type of chemical bond. The two most common
allotropes of pure carbon
allotropes of pure carbon
are diamond and
graphite Graphite (), archaically referred to as plumbago, is a crystalline form of the element carbon Carbon (from la, carbo "coal") is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table ...

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. 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 In thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, radiation, and physical properties of matter. The behavior of these quantities is governed ...
. 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/m in pure diamond. 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. Diamonds have been adopted for many uses because of the material's exceptional physical characteristics. Of all known substances, it is the hardest and least compressible. It has the highest
thermal conductivity The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k, \lambda, or \kappa. Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal ...

thermal conductivity
and the highest sound velocity. It has low adhesion and friction, and its coefficient of
thermal expansion Thermal expansion is the tendency of matter to change its shape A shape or figure is the form of an object or its external boundary, outline, or external surface File:Water droplet lying on a damask.jpg, Water droplet lying on a damask ...
is extremely low. Its optical transparency extends from the
far infrared 300px, Diagram of part of the electromagnetic spectrum Far infrared (FIR) is a region in the infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. I ...
to the deep
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, ...

ultraviolet
and it has high
optical dispersion A compact fluorescent lamp seen through an Amici prism ">Amici_prism.html" ;"title="compact fluorescent lamp seen through an Amici prism">compact fluorescent lamp seen through an Amici prism In optics, dispersion is the phenomenon in which the ...

optical dispersion
. It also has high electrical resistance. It is chemically inert, not reacting with most corrosive substances, and has excellent biological compatibility.


Thermodynamics

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 pressure, between at and at (the diamond/graphite/liquid
triple point In , the triple point of a substance is the and at which the three (, , and ) of that substance coexist in .. It is that temperature and pressure at which the curve, curve and the curve meet. For example, the triple point of occurs at a tem ...
). However, the phases have a wide region about this line where they can coexist. At
normal temperature and pressureNormal(s) or The Normal(s) may refer to: Film and television * ''Normal'' (2003 film), starring Jessica Lange and Tom Wilkinson * ''Normal'' (2007 film), starring Carrie-Anne Moss, Kevin Zegers, Callum Keith Rennie, and Andrew Airlie * ''Normal ...
, and , the stable phase of carbon is graphite, but diamond is
metastable In chemistry and physics, metastability denotes an intermediate energetic state within a dynamical system other than the system's ground state, state of least energy. A ball resting in a hollow on a slope is a simple example of metastability. I ...

metastable
and its rate of conversion to graphite is negligible. However, at temperatures above about , diamond rapidly converts to graphite. Rapid conversion of graphite to diamond requires pressures well above the equilibrium line: at , a pressure of is needed. 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. At high pressures,
silicon Silicon is a chemical element with the Symbol (chemistry), symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a Tetravalence, tetravalent metalloid and semiconductor. It is a member ...

silicon
and
germanium Germanium is a chemical element with the Symbol (chemistry), symbol Ge and atomic number 32. It is a lustrous, hard-brittle, grayish-white metalloid in the carbon group, chemically similar to its group neighbors silicon and tin. Pure germanium i ...

germanium
have a BC8
body-centered cubic 200px, A network model of a primitive cubic system In crystallography, the cubic (or isometric) crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in cryst ...
crystal structure, and a similar structure is predicted for carbon at high pressures. At , the transition is predicted to occur at . Research results published in an article in the scientific journal ''
Nature Physics ''Nature Physics'', is a monthly, peer review, peer-reviewed, scientific journal published by the Nature Research. It was first published in October 2005 (volume 1, issue 1). The chief editor is Andrea Taroni, who is a full-time professional editor ...
'' 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 giant An ice giant is a giant planet composed mainly of elements heavier than hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. With a standard atomic weight of , hydrogen is the lightest el ...
s
Neptune Neptune is the eighth and farthest-known Solar planet from the Sun. In the Solar System, it is the fourth-largest planet by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times the mass of Earth, slightly mo ...

Neptune
and
Uranus Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus, who, according to Greek mythology Greek mythology is the body of myths originally told by the Ancient Greece, ancient Greeks, 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.


Crystal structure

The most common crystal structure of diamond is called
diamond cubic The diamond cubic crystal structure is a repeating pattern of 8 atoms that certain materials may adopt as they solidify. While the first known example was diamond, other elements in group 14 also adopt this structure, including α-tin, the se ...
. It is formed of
unit cell In geometry Geometry (from the grc, γεωμετρία; ''wikt:γῆ, geo-'' "earth", ''wikt:μέτρον, -metron'' "measurement") is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space t ...

unit cell
s (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. The length of each side of the unit cell is denoted by ''a'' and is 3.567 
angstrom The angstromEntry "angstrom" in the Oxford online dictionary. Retrieved on 2019-03-02 from https://en.oxforddictionaries.com/definition/angstrom.Entry "angstrom" in the Merriam-Webster online dictionary. Retrieved on 2019-03-02 from https://www.m ...

angstrom
s. The nearest neighbour distance in the diamond lattice is 1.732''a''/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 200px, A network model of a primitive cubic system In crystallography Crystallography is the experimental science of determining the arrangement of atoms in crystalline solids (see crystal structure). The word "crystallography" is derived fro ...

face-centered cubic
lattices with one displaced by of the diagonal along a cubic cell, or as one lattice with two atoms associated with each lattice point. Viewed from a 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 Lonsdaleite (named in honour of Kathleen Lonsdale), also called hexagonal diamond in reference to the crystal structure In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecule File:Penta ...

lonsdaleite
, but this is far less common and is formed under different conditions from cubic carbon.


Crystal habit

Diamonds occur most often as
euhedral Euhedral pyrite crystals Euhedral crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that ext ...
or rounded and twinned octahedra known as ''
macle {{inline, date=April 2009 Macle is a term used in crystallography. It is a crystalline form, crystal twinning, twin-crystal or double crystal (such as chiastolite). It is crystallographic twin according to the spinel twin law and is seen in octahe ...
s''. As diamond's crystal structure has a cubic arrangement of the atoms, they have many
facet Facets () are flat faces on geometric shapes. The organization of naturally occurring facets was key to early developments in crystallography Crystallography is the experimental science of determining the arrangement of atoms in crystalline so ...
s that belong to a
cube In geometry Geometry (from the grc, γεωμετρία; ' "earth", ' "measurement") is, with , one of the oldest branches of . It is concerned with properties of space that are related with distance, shape, size, and relative position ...
, octahedron,
rhombicosidodecahedron In geometry Geometry (from the grc, γεωμετρία; ''wikt:γῆ, geo-'' "earth", ''wikt:μέτρον, -metron'' "measurement") is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space tha ...

rhombicosidodecahedron
,
tetrakis hexahedron In geometry Geometry (from the grc, γεωμετρία; ''wikt:γῆ, geo-'' "earth", ''wikt:μέτρον, -metron'' "measurement") is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space t ...
, or . 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. 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. Diamonds can also form polycrystalline aggregates. There have been attempts to classify them into groups with names such as
boart Bort, boart, or boort is an umbrella term used in the diamond industry to refer to shards of non-gemstone, gem-grade/quality diamonds. In the manufacturing and heavy industries, "bort" is used to describe dark, imperfectly formed or crystallize ...
,
ballas Ballas or shot bort Bort, boart, or boort is an umbrella term In linguistics Linguistics is the science, scientific study of language. It encompasses the analysis of every aspect of language, as well as the methods for studying and m ...
, stewartite, and framesite, but there is no widely accepted set of criteria. Carbonado, a type in which the diamond grains were
sintered image:LDClinkerScaled.jpg, Clinker (cement), Clinker nodules produced by sintering Sintering or frittage is the process of compacting and forming a solid mass of material by heat or pressure without melting it to the point of liquefaction. Sinte ...
(fused without melting by the application of heat and pressure), is black in color and tougher than single crystal diamond. It has never been observed in a volcanic rock. There are many theories for its origin, including formation in a star, but no consensus.


Mechanical properties


Hardness

Diamond is the hardest known natural material on both the Vickers scale and the
Mohs scale The Mohs scale of mineral hardness () is a qualitative ordinal scale Ordinal data is a categorical, statistical data type where the variables have natural, ordered categories and the distances between the categories are not known. These data e ...
. 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. Indeed, diamonds can be scratched by other diamonds and worn down over time even by softer materials, such as vinyl
phonograph record A phonograph disc record (also known as a gramophone disc record, especially in ), or simply a phonograph record, gramophone record, disc record, long-playing record, or record, is an in the form of a flat disc with an inscribed, modulated ...
s. 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). Therefore, whereas it might be possible to scratch some diamonds with other materials, such as
boron nitride Boron nitride is a thermally and chemically resistant refractory A refractory material or refractory is a material that is resistant to decomposition by heat, pressure, or chemical attack, and retains strength and form at high temperatures. Ref ...

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 An engagement or betrothal is the period of time between a marriage proposal and the marriage itself (which is typically but not always commenced with a wedding). During this period, a couple is said to be ''fiancés'' (from wikt:fiancé#French ...

engagement
or
wedding ring A wedding ring or wedding band is a finger ring A ring is a round band, usually of metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or ...

wedding ring
s, which are often worn every day. The hardest natural diamonds mostly originate from the Copeton and
Bingara Bingara (Aboriginal for 'creek') is a small town on the Gwydir River in Murchison County in the New England (New South Wales), New England region of New South Wales, Australia. Bingara is currently the administrative centre for the Gwydir Shire t ...
fields located in the
New England New England is a region comprising six states in the Northeastern United States The Northeastern United States (also referred to as the American Northeast, the Northeast, and the East Coast) is a geographical region In geography ...
area in
New South Wales New South Wales (abbreviated as NSW) is a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ''The State'' (newspape ...
, 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 A crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addit ...
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.


Toughness

Somewhat related to hardness is another mechanical property ''toughness'', which is a material's ability to resist breakage from forceful impact. The
toughness In materials science The Interdisciplinarity, interdisciplinary field of materials science, also commonly termed materials science and engineering, covers the design and discovery of new materials, particularly solids. The intellectual origin ...
of natural diamond has been measured as 7.5–10 
MPa MPA or mPa may refer to: Academia Academic degrees * Master of Performing Arts * Master of Professional Accountancy * Master of Public Administration * Master of Public Affairs Schools * Mesa Preparatory Academy * Morgan Park Academy * Mounds ...
·m1/2. This value is good compared to other ceramic materials, but poor compared to most engineering materials such as engineering alloys, which typically exhibit toughnesses over 100MPa·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. "Impact toughness" is one of the main indexes to measure the quality of synthetic industrial diamonds.


Yield strength

Diamond has compressive yield strength of 130–140GPa. This exceptionally high value, along with the hardness and transparency of diamond, are the reasons that
diamond anvil upright=1.2, Schematics of the core of a diamond anvil cell. The culets (tip) of the two diamond anvils are typically 100–250 microns across. A diamond anvil cell (DAC) is a high-pressure device used in geology Geology (from the Ancient Gre ...
cells are the main tool for high pressure experiments. These anvils have reached pressures of . Much higher pressures may be possible with
nanocrystalline A nanocrystalline (NC) material is a polycrystalline material with a crystallite size of only a few nanometers. These materials fill the gap between amorphous materials without any long range order and conventional coarse-grained materials. Definit ...
diamonds.


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 (~100–300nanometers in diameter, micrometers long), they can be elastically stretched by as much as 9-10 percent tensile strain without failure, with a maximum local tensile stress of , very close to the theoretical limit for this material.


Electrical conductivity

Other specialized applications also exist or are being developed, including use as
semiconductor A semiconductor material has an electrical conductivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric curre ...
s: some
blue diamond Blue diamond is a type of diamond Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic The diamond cubic crystal structure is a repeating pattern of 8 atoms that certain mater ...

blue diamond
s 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 In solid-state physics, the valence band and conduction band are the electronic band structure, bands closest to the Fermi level, and thus determine the electrical conductivity of the solid. In nonmetals, the valence electron, valence band is th ...
. Substantial conductivity is commonly observed in nominally undoped diamond grown by
chemical vapor deposition Chemical vapor deposition (CVD) is a vacuum deposition Vacuum deposition is a family of processes used to deposit layers of material atom-by-atom or molecule-by-molecule on a solid surface. These processes operate at pressures well below atmo ...
. This conductivity is associated with
hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and pressure, standard conditions hydrogen is a gas of diatomic molecules having the che ...

hydrogen
-related species adsorbed at the surface, and it can be removed by annealing or other surface treatments. A 2020 paper reported that extremely thin needles of diamond can be made to vary their electronic
band gap In solid-state physics Solid-state physics is the study of rigid matter, or solids, through methods such as quantum mechanics, crystallography, electromagnetism, and metallurgy. It is the largest branch of condensed matter physics. Solid-state ...

band gap
from the normal 5.6 eV to near zero by selective mechanical deformation.


Surface property

Diamonds are naturally
lipophilicLipophilicity (from Greek language, Greek λίπος "fat" and :wikt:φίλος, φίλος "friendly"), refers to the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene. Such non-polar ...
and
hydrophobic In chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence ...
, 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 A hydrophile is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral group of two or more atoms ...

hydrophilic
that they can stabilize multiple layers of
water iceWater ice could refer to: *Ice Ice is water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constit ...

water ice
at
human body temperature Normal human body-temperature (normothermia, euthermia) is the typical temperature Temperature is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy, present in all matter, which is the source of th ...
. 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 ) under atmospheric pressure. The structure gradually changes into sp2C above this temperature. Thus, diamonds should be reduced under this temperature.


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 to ; 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. Heat generated from cutting a diamond will not ignite the diamond, and neither will a cigarette lighter, but house fires and blow torches are hot enough. Jewelers must be careful when molding the metal in a diamond ring. Diamond powder of an appropriate grain size (around 50microns) burns with a shower of sparks after ignition from a flame. Consequently,
pyrotechnic composition A pyrotechnic composition is a substance or mixture of substances designed to produce an effect by heat, light, sound, gas/smoke or a combination of these, as a result of non-detonative self-sustaining exothermic In thermodynamics Thermodyna ...
s based on
synthetic diamondSynthetic things are composed of multiple parts, often with the implication that they are artificial. In particular, 'synthetic' may refer to: Science * Synthetic chemical or compound, produced by the process of chemical synthesis * Organic compo ...

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 also reacts with fluorine gas above about .


Color

Diamond has a wide
band gap In solid-state physics Solid-state physics is the study of rigid matter, or solids, through methods such as quantum mechanics, crystallography, electromagnetism, and metallurgy. It is the largest branch of condensed matter physics. Solid-state ...

band gap
of corresponding to the deep
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, ...

ultraviolet
wavelength of 225nanometers. 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 Nitrogen is the chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science ...

nitrogen
,
boron Boron is a chemical element with the Symbol (chemistry), symbol B and atomic number 5. Produced entirely by cosmic ray spallation and supernovae and not by stellar nucleosynthesis, it is a low-abundance element in the Solar System a ...

boron
, and
hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and pressure, standard conditions hydrogen is a gas of diatomic molecules having the che ...

hydrogen
can be introduced into diamond during the growth at significant concentrations (up to atomic percents). Transition metals
nickel Nickel is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

nickel
and
cobalt Cobalt is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical element ...

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 and even less for cobalt. Virtually any element can be introduced to diamond by ion implantation. Nitrogen is by far the most common impurity found in gem diamonds and is responsible for the yellow and brown color in diamonds. Boron is responsible for the blue color. Color in diamond has two additional sources: irradiation (usually by alpha particles), that causes the color in green diamonds, and
plastic deformation In engineering, deformation refers to the change in size or shape of an object. ''Displacements'' are the ''absolute'' change in position of a point on the object. Deflection (engineering) , Deflection is the relative change in external displace ...
of the diamond crystal lattice. Plastic deformation is the cause of color in some brown and perhaps pink and red diamonds. In order of increasing rarity, yellow diamond is followed by brown, colorless, then by blue, green, black, pink, orange, purple, and red. "Black", or
carbonado Carbonado, commonly known as black diamond, is one of the toughness, toughest forms of natural diamond. It is an impure, high-density, micro-porous form of polycrystalline diamond consisting of diamond, graphite, and amorphous carbon, with mino ...

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 In geometry and crystallography, a Bravais lattice, named after , is an infinite array of discrete points generated by a set of Translation operator (quantum mechanics)#Discrete Translational Symmetry, discrete translation operations described in th ...
, 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. 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. In 2008, the Wittelsbach Diamond, a
blue diamond Blue diamond is a type of diamond Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic The diamond cubic crystal structure is a repeating pattern of 8 atoms that certain mater ...

blue diamond
once belonging to the King of Spain, fetched over US$24 million at a Christie's auction. In May 2009, a
blue diamond Blue diamond is a type of diamond Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic The diamond cubic crystal structure is a repeating pattern of 8 atoms that certain mater ...

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). That record was, however, beaten the same year: a vivid pink diamond was sold for $10.8 million in Hong Kong on December 1, 2009.


Clarity

Clarity is one of the of 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. 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.


Identification

Diamonds can be identified by their high thermal conductivity (900–). Their high
refractive index In optics, the refractive index (also known as refraction index or index of refraction) of a optical medium, material is a dimensionless number that describes how fast EM radiation, light travels through the material. It is defined as :n = \frac ...

refractive index
is also indicative, but other materials have similar refractivity. 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. 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; 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".


Geology

Diamonds are extremely rare, with concentrations of at most parts per billion in source rock. 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. Rarely, they have been found in glacial till (notably in Wisconsin and Indiana), but these deposits are not of commercial quality. These types of deposit were derived from localized igneous intrusive rock, intrusions through weathering and sediment transport, transport by wind or water. Most diamonds come from the Mantle (geology), 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 ''Detonation nanodiamond, nanodiamonds'' to form. Impact-type microdiamonds can be used as an indicator of ancient impact craters. Popigai crater in Russia may have the world's largest diamond deposit, estimated at trillions of carats, and formed by an asteroid impact. 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 embryophyte, 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.


Surface distribution

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 2.5billion years or more. 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 ''orogeny, orogenic belt'', a weaker zone surrounding the central craton that has undergone compressional tectonics. Instead of
kimberlite Cross-section of kimberlite from South Africa. The kimberlite matrix is made up of clay minerals and carbonates, presented in blue, purple and buff colours. Kimberlite is an igneous rock, which sometimes contains diamonds. It is named after the ...

kimberlite
, the host rock is
lamproite Lamproite is an ultrapotassic mantle-derived volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. Abou ...
. Lamproites with diamonds that are not economically viable are also found in the United States, India, and Australia. In addition, diamonds in the Algoman orogeny, Wawa belt of the Superior province in Canada and microdiamonds in the Northeastern Japan arc, island arc of Japan are found in a type of rock called lamprophyre. 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. It is hybrid rock with a chaotic mixture of small minerals and rock fragments (clastic rock, 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 subgroup, 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 (). 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 Volatility (chemistry), volatiles and magnesium oxide, and are less redox, oxidizing than more common mantle melts such as basalt. These characteristics allow the melts to carry diamonds to the surface before they dissolve.


Exploration

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 survey, geophysical methods such as aeromagnetic surveys, electrical resistivity tomography, 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 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.


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–strontium dating, rubidium to strontium, Samarium–neodymium dating, samarium to neodymium, Uranium–lead dating, uranium to lead, Argon–argon dating, argon-40 to argon-39, or Rhenium–osmium dating, rhenium to osmium. Those found in kimberlites have ages ranging from , 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 Mine, Premier and Wawa). Thus, the kimberlites formed independently of the diamonds and served only to transport them to the surface. 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.


Origin in mantle

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. Host rocks in a mantle keel include harzburgite and lherzolite, two type of peridotite. The most dominant rock type in the upper mantle (Earth), upper mantle, peridotite is an
igneous rock Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main The three types of rocks, rock types, the others being Sedimentary rock, sedimentary and metamorphic rock, metamorphic. Igneous rock is ...
consisting mostly of the minerals olivine and pyroxene; it is low in Silicon dioxide, silica and high in magnesium. However, diamonds in peridotite rarely survive the trip to the surface. 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, subduction zone. A smaller fraction of diamonds (about 150 have been studied) come from depths of 330–660 km, a region that includes the Transition zone (Earth), 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. Diamond is thermodynamically stable at high pressures and temperatures, with the phase transition from
graphite Graphite (), archaically referred to as plumbago, is a crystalline form of the element carbon Carbon (from la, carbo "coal") is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table ...

graphite
occurring at greater temperatures as the pressure increases. Thus, underneath continents it becomes stable at temperatures of 950degrees Celsius and pressures of 4.5 gigapascals, corresponding to depths of 150kilometers or greater. In subduction zones, which are colder, it becomes stable at temperatures of 800 °C and pressures of 3.5gigapascals. 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. 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.


Carbon sources

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


Formation and growth

Diamonds in the mantle form through a ''metasomatism, 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. 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.


Transport to the surface

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 exsolution, 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 ). 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.


Double diamonds

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


In space

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 Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus, who, according to Greek mythology Greek mythology is the body of myths originally told by the Ancient Greece, ancient Greeks, and ...

Uranus
and
Neptune Neptune is the eighth and farthest-known Solar planet from the Sun. In the Solar System, it is the fourth-largest planet by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times the mass of Earth, slightly mo ...

Neptune
. Some extrasolar planets may be almost entirely composed of diamond. Diamonds may exist in carbon-rich stars, particularly white dwarfs. One theory for the origin of
carbonado Carbonado, commonly known as black diamond, is one of the toughness, toughest forms of natural diamond. It is an impure, high-density, micro-porous form of polycrystalline diamond consisting of diamond, graphite, and amorphous carbon, with mino ...

carbonado
, the toughest form of diamond, is that it originated in a white dwarf or supernova. Diamonds formed in stars may have been the first minerals.


Industry

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

The Dispersion (optics), 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 ''Carat (unit), carats'' (a carat being equal to 0.2grams), ''Diamond cut, cut'' (quality of the cut is graded according to aspect ratio, proportions, symmetry and polishing, polish), ''Diamond color, color'' (how close to white or colorless; for fancy diamonds how intense is its hue), and ''Diamond clarity, clarity'' (how free is it from inclusion (mineral), inclusions). A large, flawless diamond is known as a Paragon (diamond), 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.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. 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 diamond mine, Jwaneng mine in Botswana, which is a single large-pit mine that can produce between of diamonds per year). 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). The production and distribution of diamonds is largely consolidated in the hands of a few key players, and concentrated in traditional diamond trading centers, the most important being Antwerp, where 80% of all rough diamonds, 50% of all cut diamonds and more than 50% of all rough, cut and industrial diamonds combined are handled. This makes Antwerp a de facto "world diamond capital". The city of Antwerp also hosts the Antwerpsche Diamantkring, created in 1929 to become the first and biggest diamond bourse dedicated to rough diamonds. Another important diamond center is New York City, where almost 80% of the world's diamonds are sold, including auction sales. 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 (business), 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, but by 2001–2009 the figure had decreased to around 45%, and by 2013 the company's market share had further decreased to around 38% in value terms and even less by volume. De Beers sold off the vast majority of its diamond stockpile in the late 1990s – early 2000s and the remainder largely represents working stock (diamonds that are being sorted before sale). This was well documented in the press 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. As of January 2011, De Beers states that it only sells diamonds from the following four countries: Botswana, Namibia, South Africa and Canada. Alrosa had to suspend their sales in October 2008 due to the 2000s energy crisis, global energy crisis, but the company reported that it had resumed selling rough diamonds on the open market by October 2009. Apart from Alrosa, other important diamond mining companies include BHP, which is the world's largest mining company; Rio Tinto (corporation), Rio Tinto, the owner of the Argyle diamond mine, Argyle (100%), Diavik Diamond Mine, Diavik (60%), and Murowa diamond mine, Murowa (78%) diamond mines; and Petra Diamonds, the owner of several major diamond mines in Africa. 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. 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. 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). The cutting and polishing of rough diamonds is a specialized skill that is concentrated in a limited number of locations worldwide. Traditional diamond cutting centers are Antwerp, Amsterdam, Johannesburg, New York City, and Tel Aviv. Recently, diamond cutting centers have been established in China, India, Thailand, Namibia and Botswana. Cutting centers with lower cost of labor, notably Surat in Gujarat, Gujarat, India, handle a larger number of smaller carat diamonds, while smaller quantities of larger or more valuable diamonds are more likely to be handled in Europe or North America. The recent expansion of this industry in India, employing low cost labor, has allowed smaller diamonds to be prepared as gems in greater quantities than was previously economically feasible. Diamonds prepared as gemstones are sold on diamond exchanges called ''Exchange (organized market), bourses''. There are 28 registered diamond bourses in the world. 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.


Cutting

Mined rough diamonds are converted into gems through a multi-step process called "cutting". Diamonds are extremely hard, but also brittle and can be split up by a single blow. Therefore, diamond cutting is traditionally considered as a delicate procedure requiring skills, scientific knowledge, tools and experience. Its final goal is to produce a faceted jewel where the specific angles between the facets would optimize the diamond luster, that is dispersion of white light, whereas the number and area of facets would determine the weight of the final product. The weight reduction upon cutting is significant and can be of the order of 50%. Several possible shapes are considered, but the final decision is often determined not only by scientific, but also practical considerations. For example, the diamond might be intended for display or for wear, in a ring or a necklace, singled or surrounded by other gems of certain color and shape. Some of them may be considered as classical, such as Diamond cut, round, Pear Cut Diamond, pear, Marquise Diamond, marquise, Oval Cut Diamond, oval, hearts and arrows diamonds, etc. Some of them are special, produced by certain companies, for example, Phoenix Cut Diamond, Phoenix, Cushion Cut Diamond, Cushion, Sole Mio Cut Diamond, 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: * 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. After initial cutting, the diamond is shaped in numerous stages of polishing. Unlike cutting, which is a responsible but quick operation, polishing removes material by gradual erosion and is extremely time-consuming. The associated technique is well developed; it is considered as a routine and can be performed by technicians. After polishing, the diamond is reexamined for possible flaws, either remaining or induced by the process. Those flaws are concealed through various diamond enhancement techniques, such as repolishing, crack filling, or clever arrangement of the stone in the jewelry. Remaining non-diamond inclusions are removed through laser drilling and filling of the voids produced.


Marketing

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, but this was not a concern as De Beers dominated the diamond market throughout the 20th century. De Beers' market share dipped temporarily to 2nd 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. 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. The campaign was perhaps best captured by the slogan "a diamond is forever". This slogan is now being used by De Beers Diamond Jewelers, 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. The change was mostly due to the numbers: the Argyle mine, with its of diamonds per year, makes about one-third of global production of natural diamonds; 80% of Argyle diamonds are brown.


Industrial-grade diamonds

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. 80% of mined diamonds (equal to about annually) are unsuitable for use as gemstones and are used industrially. In addition to mined diamonds, synthetic diamonds found industrial applications almost immediately after their invention in the 1950s; another of synthetic diamond is produced annually for industrial use (in 2004; in 2014 it is , 90% of which is produced in China). Approximately 90% of diamond Grinding (abrasive cutting), grinding grit is currently of synthetic origin. 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. 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. Specialized applications include use in laboratories as containment for Pressure experiment, high-pressure experiments (see
diamond anvil cell upright=1.2, Schematics of the core of a diamond anvil cell. The culets (tip) of the two diamond anvils are typically 100–250 microns across. A diamond anvil cell (DAC) is a high-pressure In science Science (from the Latin word ''scientia' ...

diamond anvil cell
), high-performance bearing (mechanical), bearings, and limited use in specialized windows. With the continuing advances being made in the production of synthetic diamonds, future applications are becoming feasible. The high
thermal conductivity The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k, \lambda, or \kappa. Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal ...

thermal conductivity
of diamond makes it suitable as a heat sink for integrated circuits in electronics.


Mining

Approximately of diamonds are mined annually, with a total value of nearly US$9 billion, and about are synthesized annually. Roughly 49% of diamonds originate from Central Africa, Central and Southern Africa, although significant sources of the mineral have been discovered in Canada, India, Russia, Brazil, and Australia. They are mined from kimberlite and lamproite volcanic pipes, which can bring diamond crystals, originating from deep within the Earth where high pressures and temperatures enable them to form, to the surface. The mining and distribution of natural diamonds are subjects of frequent controversy such as concerns over the sale of ''blood diamonds'' or ''conflict diamonds'' by African paramilitary groups. The diamond supply chain is controlled by a limited number of powerful businesses, and is also highly concentrated in a small number of locations around the world. 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, the separation was done with grease belts; diamonds have a stronger tendency to stick to grease than the other minerals in the ore. Historically, diamonds were found only in alluvial deposits in Guntur district, Guntur and Krishna district of the Krishna River delta in Southern India. India led the world in diamond production from the time of their discovery in approximately the 9th century BC to the mid-18th century AD, but the commercial potential of these sources had been exhausted by the late 18th century and at that time India was eclipsed by Brazil where the first non-Indian diamonds were found in 1725. Currently, one of the most prominent Indian mines is located at Panna District, Panna. Diamond extraction from primary deposits (kimberlites and lamproites) started in the 1870s after the discovery of the Diamond Fields in South Africa. Production has increased over time and now an accumulated total of have been mined since that date. 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. In the U.S., diamonds have been found in Arkansas, Colorado, New Mexico, Wyoming, and Montana. 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. Today, most commercially viable diamond deposits are in Russia (mostly in Sakha Republic, for example Mir Mine, Mir pipe and Udachnaya pipe), Botswana, Australia (Northern Australia, Northern and Western Australia) and the Democratic Republic of the Congo. 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 42metric tons per year in the 1990s. There are also commercial deposits being actively mined in the Northwest Territories of Canada and Brazil. Diamond prospectors continue to search the globe for diamond-bearing kimberlite and lamproite pipes.


Political issues

] In some of the more politically unstable central African and west African countries, revolutionary groups have taken control of List of diamond mines, diamond mines, using proceeds from diamond sales to finance their operations. Diamonds sold through this process are known as ''conflict diamonds'' or ''blood diamonds''. In response to public concerns that their diamond purchases were contributing to war and human rights abuses in central Africa, central and West Africa, western Africa, the United Nations, the diamond industry and diamond-trading nations introduced the Kimberley Process in 2002. The Kimberley Process aims to ensure that conflict diamonds do not become intermixed with the diamonds not controlled by such rebel groups. This is done by requiring diamond-producing countries to provide proof that the money they make from selling the diamonds is not used to fund criminal or revolutionary activities. Although the Kimberley Process has been moderately successful in limiting the number of conflict diamonds entering the market, some still find their way in. According to the International Diamond Manufacturers Association, conflict diamonds constitute 2–3% of all diamonds traded. 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". The Canadian Government has set up a body known as the Canadian Diamond Code of Conduct to help authenticate Canadian diamonds. This is a stringent tracking system of diamonds and helps protect the "conflict free" label of Canadian diamonds.


Synthetics, simulants, and enhancements


Synthetics

Synthetic diamonds are diamonds manufactured in a laboratory, as opposed to diamonds mined from the Earth. The gemological and industrial uses of diamond have created a large demand for rough stones. This demand has been satisfied in large part by synthetic diamonds, which have been manufactured by various processes for more than half a century. However, in recent years it has become possible to produce gem-quality synthetic diamonds of significant size. It is possible to make colorless synthetic gemstones that, on a molecular level, are identical to natural stones and so visually similar that only a gemologist with special equipment can tell the difference. The majority of commercially available synthetic diamonds are yellow and are produced by so-called ''high-pressure high-temperature'' (HPHT) processes. The yellow color is caused by
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impurities. Other colors may also be reproduced such as blue, green or pink, which are a result of the addition of
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or from irradiation after synthesis. Another popular method of growing synthetic diamond is
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(CVD). The growth occurs under low pressure (below atmospheric pressure). It involves feeding a mixture of gases (typically to
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hydrogen
) into a chamber and splitting them into chemically active radical (chemistry), radicals in a plasma (physics), plasma ignited by microwaves, hot filament, electric arc, arc discharge, welding torch, or laser. This method is mostly used for coatings, but can also produce single crystals several millimeters in size (see picture). As of 2010, nearly all 5,000 million carats (1,000tonnes) of synthetic diamonds produced per year are for industrial use. Around 50% of the 133 million carats of natural diamonds mined per year end up in industrial use. Mining companies' expenses average 40 to 60 US dollars per carat for natural colorless diamonds, while synthetic manufacturers' expenses average for synthetic, gem-quality colorless diamonds. However, a purchaser is more likely to encounter a synthetic when looking for a fancy-colored diamond because nearly all synthetic diamonds are fancy-colored, while only 0.01% of natural diamonds are.


Simulants

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.


Enhancements

Diamond enhancements are specific treatments performed on natural or synthetic diamonds (usually those already cut and polished into a gem), which are designed to better the gemological characteristics of the stone in one or more ways. These include laser drilling to remove inclusions, application of sealants to fill cracks, treatments to improve a white diamond's color grade, and treatments to give fancy color to a white diamond. Coatings are increasingly used to give a diamond simulant such as cubic zirconia a more "diamond-like" appearance. One such substance 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.


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. 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. "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. Laboratories use techniques such as spectroscopy, microscopy, and luminescence under shortwave ultraviolet light to determine a diamond's origin. 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 Diamond Trading Company, DTC and marketed by the GIA. 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 Diamond Spotter. Stones in the D-Z color range can be examined through the DiamondSure UV/visible spectrometer, a tool developed by De Beers. 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 grc, ἀδάμας (''adámas''), 'proper, unalterable, unbreakable, untamed', from :wiktionary:ἀ-, ἀ- (''a-''), 'not' + grc, δαμάω (''damáō''), 'to overpower, tame'. 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 River, Penner, Krishna River, Krishna, and Godavari River, Godavari. Diamonds have been known in India for at least 3,000years but most likely 6,000years. Diamonds have been treasured as gemstones since their use as icon, religious icons in Kingdoms of Ancient India, ancient India. Their usage in engraving tools also dates to early History of the world, human history. The popularity of diamonds has risen since the 19th century because of increased supply, improved cutting and polishing techniques, growth in the world economy, and innovative and successful advertising campaigns. In 1772, the French scientist Antoine Lavoisier used a lens to concentrate the rays of the sun on a diamond in an atmosphere of oxygen, and showed that the only product of the combustion was carbon dioxide, proving that diamond is composed of carbon. Later in 1797, the English chemist Smithson Tennant repeated and expanded that experiment.Smithson Tennant (1797
"On the nature of the diamond"
''Philosophical Transactions of the Royal Society of London'', 87: 123–127.
By demonstrating that burning diamond and graphite releases the same amount of gas, he established the chemical equivalence of these substances.


See also

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


References


Books

* * * * * * * * * * * * * * *


External links


Properties of diamond: Ioffe database
* (2007) Gemological Institute of America (GIA) * Tyson, Peter (November 2000)

Retrieved March 10, 2005.
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