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{{Short description|Form of carbon}}
{{About|diamond as a mineral|the use of diamond as a gemstone|Diamond (gemstone)|other uses}}
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{{Infobox mineral
|name = Diamond
|category = [[Native element minerals|Native minerals]]
|boxwidth =
|boxbgcolor = #7da7d9
|image = Rough Diamond.jpg
|imagesize = 260px
|alt = An irregular shaped brownish diamond
|caption = A [[rough diamond]]{{efn|The brownish hue is due to superficial ferrous impurities that constitute evidence of the geological sedimentary context in which it was found. This diamond is potentially colorless.<ref>{{cite web|website=Royal Treasure Museum|title=Gold and Diamonds from Brazil|url=https://www.tesouroreal.pt/en/pages/b9ed8b00-ouro-e-diamantes-do-brasil|access-date=April 18, 2025}}</ref>}}
|formula = [[Carbon|C]]
| IMAsymbol = Dia<ref>{{Cite journal| vauthors = Warr LN |date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free| issn=0026-461X}}</ref> 
|molweight = {{val|12.01|ul=g/mol}}
|strunz = 1.CB.10a
|dana = 1.3.6.1
|color = Typically yellow, brown, or gray to colorless. Less often blue, green, black, translucent white, pink, violet, orange, purple, and red.
|habit = [[Octahedral]]
|system = [[Cubic crystal system|Cubic]]
|class = Hexoctahedral (m{{Overline|3}}m) <br/>[[H-M symbol]]: (4/m {{Overline|3}} 2/m)
|symmetry = ''F''d{{overline|3}}m (No. 227)
|twinning = Spinel law common (yielding "macle")
|cleavage = 111 (perfect in four directions)
|fracture = Irregular/Uneven
|mohs = 10 (defining mineral)
|luster = [[Adamantine lustre|Adamantine]]
|polish = Adamantine
|refractive = 2.418 (at 500&nbsp;nm)
|opticalprop = Isotropic
|birefringence = None
|dispersion = 0.044
|pleochroism = None
|streak = Colorless
|melt = [[Carbon#Characteristics|Pressure dependent]]
|gravity = {{val|3.52|0.01}}
|density = {{val|3.5|-|3.53|ul=g/cm3}}
{{val|3500|-|3530|ul=kg/m3}}
|diaphaneity = [[Transparency (optics)|Transparent]] to subtransparent to translucent
|references =<ref name=mindat/><ref>{{cite web|publisher=WebMineral|title=Diamond|url=http://webmineral.com/data/Diamond.shtml|access-date=July 7, 2009|archive-date=January 7, 2019|archive-url=https://web.archive.org/web/20190107071332/http://webmineral.com/data/Diamond.shtml|url-status=live}}</ref>
|SMILES = C1(C2(C7))C3(C89)C(C4(C0))C5CC1C(C1)C(C5(C5))C36C3(C21)C(C78)C(C1)C(C90)C6(C54)CC1C3
|Jmol = C1(C2(C7))C3(C89)C(C4(C0))C5CC1C(C1)C(C5(C5))C36C3(C21)C(C78)C(C1)C(C90)C6(C54)CC1C3
}}
[[File:Diamant gisements.jpg|thumb|upright=1.25|Main diamond producing countries]]

'''Diamond''' is a [[Allotropes of carbon|solid form of the element carbon]] with its atoms arranged in a [[crystal structure]] called [[diamond cubic]]. Diamond is tasteless, odorless, strong, brittle solid, colorless in pure form, a poor conductor of electricity, and insoluble in water. Another solid form of carbon known as [[graphite]] is the [[Chemical stability|chemically stable]] form of carbon at [[Standard temperature and pressure|room temperature and pressure]], but diamond is [[metastable]] and converts to it at a negligible rate under those conditions. Diamond has the highest [[Scratch hardness|hardness]] and [[thermal conductivity]] of any natural material, properties that are used in major industrial applications such as cutting and polishing tools.

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

Most natural diamonds have ages between 1&nbsp;billion and 3.5&nbsp;billion years. Most were formed at depths between {{convert|150|and|250|km}} in the Earth's [[mantle (geology)|mantle]], although a few have come from as deep as {{convert|800|km}}. 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]]s and deposited in [[igneous rock]]s known as [[kimberlite]]s and [[lamproite]]s.

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

== Etymology, earliest use and composition discovery ==
The name ''diamond'' is derived from {{langx|grc|ἀδάμας}} (''adámas''), 'proper, unalterable, unbreakable, untamed', from [[:wiktionary:ἀ-|ἀ-]] (''a-''), 'not' + {{langx|grc|δαμάω}} (''damáō''), 'to overpower, tame'.<ref>{{cite web |vauthors=Liddell HG, Scott R |title=Adamas |work=A Greek-English Lexicon |url=https://www.perseus.tufts.edu/cgi-bin/ptext?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3D%231145 |publisher=[[Perseus Project]] |access-date=February 20, 2021 |archive-date=November 9, 2023 |archive-url=https://web.archive.org/web/20231109174330/http://www.perseus.tufts.edu/hopper/invalidquery.jsp?doc=Perseus:text:1999.04.0057:entry=entry=#1145 |url-status=live }}</ref> Diamonds are thought to have been first recognized and mined in [[India]], where significant [[alluvial deposit]]s 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 3,000{{nbsp}}years but most likely 6,000{{nbsp}}years.<ref name=hershey>{{cite book |url=https://books.google.com/books?id=35eij1e1al8C&pg=PA23 |vauthors=Hershey W |title=The Book of Diamonds |publisher=Hearthside Press |location=New York |year=2004|edition=Reprint|orig-date=1940 |pages=22–28 |isbn=978-1-4179-7715-4 |access-date=November 9, 2020 |archive-date=November 9, 2023 |archive-url=https://web.archive.org/web/20231109174422/https://books.google.com/books?id=35eij1e1al8C&pg=PA23 |url-status=live }}</ref>

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 [[human history]].<ref>{{cite book|author=Pliny the Elder|author-link=Pliny the Elder|title=Natural History: A Selection|publisher=[[Penguin Books]]|page=371|year=2004|isbn=978-0-14-044413-1}}</ref><ref name=ancient_China>{{cite news|title=Chinese made first use of diamond|url=https://news.bbc.co.uk/2/hi/science/nature/4555235.stm|work=BBC News|date=May 17, 2005|access-date=March 21, 2007|archive-date=March 20, 2007|archive-url=https://web.archive.org/web/20070320064349/http://news.bbc.co.uk/2/hi/science/nature/4555235.stm|url-status=live}}</ref> 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.<ref name=sell>{{cite web|vauthors=Epstein EJ|title=Have You Ever Tried To Sell a Diamond?|url=https://www.theatlantic.com/issues/82feb/8202diamond1.htm|work=[[The Atlantic]]|year=1982|access-date=May 5, 2009|archive-date=May 17, 2008|archive-url=https://web.archive.org/web/20080517125715/http://www.theatlantic.com/issues/82feb/8202diamond1.htm|url-status=live}}</ref>

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.<ref>See: {{unbulleted list citebundle
|1 = {{Citation |vauthors=Lavoisier A |orig-date=1772 (part 2) |date=October 15, 2007 |title=Premier mémoire sur la destruction du diamant par le feu |trans-title=First memoir on the destruction of diamond by fire |work=Histoire de l'Académie royale des sciences, avec les Mémoires de Mathématique & de Physique, tirés des registres de cette Académie |trans-journal=History of the Royal Academy of Sciences, with the Memoirs of Mathematics & Physics, drawn from the records of this academy] |via=Gallica |publisher=Académie des sciences |pages=564–591 |language=fr |issn=1967-4783 |id=ark:/12148/bpt6k35711 |url=http://gallica.bnf.fr/ark:/12148/bpt6k35711/f739.image |access-date=July 1, 2022 |archive-date=May 9, 2022 |archive-url=https://web.archive.org/web/20220509130518/https://gallica.bnf.fr/ark:/12148/bpt6k35711/f739.image |url-status=live }}
|2 = {{Citation |vauthors=Lavoisier A |orig-date=1772 (part 2) |date=October 15, 2007 |title=Second mémoire sur la destruction du diamant par le feu |trans-title=Second memoir on the destruction of diamond by fire |work=Histoire de l'Académie royale des sciences, avec les Mémoires de Mathématique & de Physique, tirés des registres de cette Académie |via=Gallica |publisher=Académie des sciences |pages=591–616 |language=fr |issn=1967-4783 |id=ark:/12148/bpt6k35711 |url=http://gallica.bnf.fr/ark:/12148/bpt6k35711/f766.image |access-date=July 1, 2022 |archive-date=July 10, 2022 |archive-url=https://web.archive.org/web/20220710231047/https://gallica.bnf.fr/ark:/12148/bpt6k35711/f766.image |url-status=live }} <!-- catalog-url=http://catalogue.bnf.fr/ark:/12148/cb32786820s --> 
}}</ref> Later, in 1797, the English chemist [[Smithson Tennant]] repeated and expanded that experiment.<ref>{{Cite journal |vauthors=Smithson T |orig-date=December 15, 1797 |title=On the nature of the diamond |journal=Philosophical Transactions of the Royal Society of London |year=1797 |volume=87 |pages=123–127 |doi=10.1098/rstl.1797.0005 |s2cid=186213726 |url=https://books.google.com/books?id=vlBFAAAAcAAJ&pg=PA123 |access-date=July 1, 2022 |doi-access=free |archive-date=February 19, 2023 |archive-url=https://web.archive.org/web/20230219072828/https://books.google.com/books?id=vlBFAAAAcAAJ&pg=PA123 |url-status=live }}</ref> By demonstrating that burning diamond and graphite releases the same amount of gas, he established the chemical equivalence of these substances.<ref name=hazen/>

== Properties ==
{{Main|Material properties of diamond}}
Diamond is a solid form of pure carbon with its atoms arranged in a crystal. Solid carbon comes in different forms known as [[allotrope]]s depending on the type of chemical bond. The two most common [[allotropes of carbon|allotropes of pure carbon]] are diamond and [[graphite]]. In graphite, the bonds are sp<sup>2</sup> [[orbital hybridisation|orbital hybrids]] and the atoms form in planes, with each bound to three nearest neighbors, 120 degrees apart. In diamond, they are sp<sup>3</sup> and the atoms form tetrahedra, with each bound to four nearest neighbors.<ref>{{cite book | vauthors = Delhaes P |chapter=Polymorphism of carbon | veditors = Delhaes P |title=Graphite and precursors |date=2000 |publisher=Gordon & Breach |isbn=978-90-5699-228-6 |pages=1–24}}</ref><ref>{{cite book | vauthors = Pierson HO |title=Handbook of carbon, graphite, diamond, and fullerenes: properties, processing, and applications |date=2012 |publisher=Noyes Publications |isbn=978-0-8155-1739-9 |pages=40–41}}</ref> 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 [[compressibility|compressible]].<ref>{{cite book | vauthors = Angus JC |chapter=Structure and thermochemistry of diamond |pages=9–30 | veditors = Paoletti A, Tucciarone A |title=The physics of diamond |date=1997 |publisher=IOS Press |isbn=978-1-61499-220-2}}</ref><ref name=ChemThermo>{{cite book | vauthors = Rock PA |title=Chemical Thermodynamics |date=1983 |publisher=University Science Books |isbn=978-1-891389-32-0 |pages=257–260}}</ref> 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&nbsp;kg/m{{sup|3}} in pure diamond.<ref name=mindat>{{cite web |publisher=Mindat |title=Diamond |url=https://www.mindat.org/min-1282.html |access-date=July 7, 2009 |archive-date=May 6, 2009 |archive-url=https://web.archive.org/web/20090506083109/http://www.mindat.org/min-1282.html |url-status=live }}</ref> 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.<ref>{{cite journal |vauthors=Gray T |title=Gone in a Flash |url=https://www.popsci.com/diy/article/2009-08/burn-diamonds-torch-and-liquid-oxygen/ |journal=Popular Science |date=October 8, 2009 |access-date=October 31, 2018 |archive-date=March 7, 2020 |archive-url=https://web.archive.org/web/20200307065622/https://www.popsci.com/diy/article/2009-08/burn-diamonds-torch-and-liquid-oxygen/ |url-status=live }}</ref>

Diamonds have been adopted for many uses because of the material's exceptional physical characteristics. It has the highest [[thermal conductivity]] and the highest sound velocity. It has low adhesion and friction, and its coefficient of [[thermal expansion]] is extremely low. Its optical transparency extends from the [[far infrared]] to the deep [[ultraviolet]], and it has high [[optical dispersion]]. It also has high electrical resistance. It is chemically inert, not reacting with most corrosive substances, and has excellent biological compatibility.<ref>{{cite book | vauthors = Chen Y, Zhang L |title=Polishing of diamond materials: mechanisms, modeling and implementation |url=https://archive.org/details/polishingdiamond00chen |url-access=limited |date=2013 |publisher=Springer Science & Business Media |isbn=978-1-84996-408-1 |pages=[https://archive.org/details/polishingdiamond00chen/page/n9 1]–2}}</ref>

=== Thermodynamics ===
[[File:Carbon-phase-diagramp.svg|thumb|Theoretically predicted [[phase diagram]] of carbon]]
The equilibrium pressure and temperature conditions for a transition between graphite and diamond are well established theoretically and experimentally. The equilibrium pressure varies linearly with temperature, between {{val|1.7|ul=GPa}} at {{val|0|u=K}} and {{val|12|u=GPa}} at {{val|5000|u=K}} (the diamond/graphite/liquid [[triple point]]).<ref name=Bundy>{{cite journal | vauthors =  Bundy P, Bassett WA, Weathers MS, Hemley RJ, Mao HK, Goncharov AF |title=The pressure-temperature phase and transformation diagram for carbon; updated through 1994 |journal=Carbon |date=1996 |volume=34 |issue=2 |pages=141–153 |doi=10.1016/0008-6223(96)00170-4|bibcode=1996Carbo..34..141B }}</ref><ref>{{cite book| vauthors = Wang CX, Yang GW |chapter=Thermodynamic and kinetic approaches of diamond and related nanomaterials formed by laser ablation in liquid| veditors = Yang G |title=Laser ablation in liquids: principles and applications in the preparation of nanomaterials |date=2012 |publisher=Pan Stanford |isbn=978-981-4241-52-6 |pages=164–165}}</ref> However, the phases have a wide region about this line where they can coexist. At [[standard temperature and pressure]], {{convert|20|C|K}} and {{convert|1|atm|MPa}}, the stable phase of carbon is graphite, but diamond is [[metastable]], with a significant kinetic energy barrier that the atoms must overcome to reach the lower energy state,<ref name=baird>{{cite web | title=Why do diamonds last forever? | website=Science Questions with Surprising Answers|first=Christopher S.|last=Baird|publisher=West Texas A&M University| date=December 17, 2013 | url=https://www.wtamu.edu/~cbaird/sq/2013/12/17/why-do-diamonds-last-forever/}}</ref> and its rate of conversion to graphite is negligible, with a timescale of millions to billions of years.<ref name=ChemThermo/><ref name=baird/> However, at temperatures above about {{val|4500|u=K}}, diamond rapidly converts to graphite. Experiments have found that diamond, in the presence of {{chem2|H2O}} passes through an intermediate linear carbon phase.<ref>{{cite journal | last1=O'Bannon | first1=E. | last2=Xia | first2=G. | last3=Shi | first3=F. | last4=Wirth | first4=R. | last5=King | first5=A. | last6=Dobrzhinetskaya | first6=L. | title=The transformation of diamond to graphite: Experiments reveal the presence of an intermediate linear carbon phase | journal=Diamond and Related Materials | volume=108 | date=2020 | doi=10.1016/j.diamond.2020.107876 | doi-access=free | article-number=107876 | bibcode=2020DRM...10807876O | osti=1631913 | url=https://www.osti.gov/servlets/purl/1631913}}</ref>

Rapid conversion of graphite to diamond requires pressures well above the equilibrium line: at {{val|2000|u=K}}, a pressure of {{val|35|u=GPa}} (about 350,000 standard atmospheres) is needed.<ref name=Bundy/>

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.<ref>{{cite journal | vauthors = Wang X, Scandolo S, Car R | title = Carbon phase diagram from ab initio molecular dynamics | journal = Physical Review Letters | volume = 95 | issue = 18 | article-number = 185701 | date = October 2005 | pmid = 16383918 | doi = 10.1103/PhysRevLett.95.185701 | bibcode = 2005PhRvL..95r5701W }}</ref> At high pressures, [[silicon]] and [[germanium]] have a BC8 [[Cubic crystal system|body-centered cubic]] crystal structure, and a similar structure is predicted for carbon at high pressures. At {{val|0|u=K}}, the transition is predicted to occur at {{val|1100|u=GPa}}.<ref>{{cite journal | vauthors = Correa AA, Bonev SA, Galli G | title = Carbon under extreme conditions: phase boundaries and electronic properties from first-principles theory | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 103 | issue = 5 | pages = 1204–1208 | date = January 2006 | pmid = 16432191 | pmc = 1345714 | doi = 10.1073/pnas.0510489103 | doi-access = free | bibcode = 2006PNAS..103.1204C }}</ref>

Results published in ''[[Nature Physics]]'' in 2010 suggest that, at ultra-high pressures and temperatures (about 10&nbsp;million atmospheres or 1&nbsp;TPa and 50,000&nbsp;°C), diamond melts into a metallic fluid. The extreme conditions required for this to occur are present in the [[ice giant]] [[planet]]s [[Neptune]] and [[Uranus]], both of which are made up of approximately 10 percent carbon and could hypothetically contain oceans of liquid carbon. Since large quantities of metallic fluid can affect the magnetic field, this could serve to explain why the geographic and magnetic poles of the two planets are not aligned.<ref>{{cite news |title=Diamond oceans possible on Uranus, Neptune | vauthors = Bland E |newspaper=Discovery News |date=January 15, 2010| archive-url=https://web.archive.org/web/20120311163132/http://news.discovery.com/space/diamond-oceans-jupiter-uranus.html | archive-date=March 11, 2012|url=http://news.discovery.com/space/diamond-oceans-jupiter-uranus.html |access-date=January 16, 2010}}</ref><ref>{{cite journal |title=Diamond: Molten under pressure |vauthors=Silvera I |journal=Nature Physics |volume=6 |pages=9–10 |year=2010 |issue=1 |bibcode=2010NatPh...6....9S |url=http://nrs.harvard.edu/urn-3:HUL.InstRepos:9121282 |doi=10.1038/nphys1491 |s2cid=120836330 |access-date=November 9, 2020 |archive-date=July 30, 2022 |archive-url=https://web.archive.org/web/20220730040414/https://dash.harvard.edu/handle/1/9121282 |url-status=live }}</ref>

=== Crystal structure ===
{{See also|Crystallographic defects in diamond}}
[[File:Diamond structure.gif|thumb|Diamond unit cell, showing the tetrahedral structure]]
The most common crystal structure of diamond is called [[diamond cubic]]. It is formed of [[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.<ref>{{cite book | vauthors = Rajendran V |title=Materials science |date=2004 |publisher=Tata McGraw-Hill Pub |isbn=978-0-07-058369-6 |page=2.16}}</ref> The length of each side of the unit cell is denoted by ''a'' and is 3.567&nbsp;[[angstrom]]s.<ref name=Ashcroft>{{cite book | vauthors = Ashcroft NW, Mermin ND |title=Solid state physics |date=1976 |publisher=Holt, Rinehart and Winston |isbn=978-0-03-083993-1 |page=[https://archive.org/details/solidstatephysic00ashc/page/76 76] |url-access=registration |url=https://archive.org/details/solidstatephysic00ashc/page/76 }}</ref>

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

A diamond cubic lattice can be thought of as two interpenetrating [[face-centered cubic]] lattices with one displaced by {{frac|1|4}} of the diagonal along a cubic cell, or as one lattice with two atoms associated with each lattice point.<ref name=Ashcroft/> Viewed from a {{math|&lt;1 1 1&gt;}} [[Miller index|crystallographic direction]], it is formed of layers stacked in a repeating ABCABC ... pattern. Diamonds can also form an ABAB ... structure, which is known as hexagonal diamond or [[lonsdaleite]], but this is far less common and is formed under different conditions from cubic carbon.<ref>{{cite book |chapter=Molecular models of porous carbons| vauthors = Bandosz TJ, Biggs MJ, Gubbins KE, Hattori Y, Iiyama T, Kaneko T, Pikunic J, Thomson K | veditors = Radovic LR |title=Chemistry and physics of carbon |volume=28 |date=2003 |publisher=Marcel Dekker |isbn=978-0-8247-0987-7 |pages=46–47}}</ref>

=== Crystal habit ===
[[File:Diamond face trigons scale.jpg|thumb|alt=A triangular facet of a crystal having triangular etch pits with the largest having a base length of about {{Convert|0.2|mm}}|One face of an uncut octahedral diamond, showing trigons (of positive and negative relief) formed by natural chemical etching]]
Diamonds occur most often as [[euhedral]] or rounded [[octahedron|octahedra]] and [[crystal twinning|twinned]] octahedra known as ''[[macle]]s''. As diamond's crystal structure has a cubic arrangement of the atoms, they have many [[facet]]s that belong to a [[cube (geometry)|cube]], octahedron, [[rhombicosidodecahedron]], [[tetrakis hexahedron]], or [[disdyakis dodecahedron]]. The crystals can have rounded-off and unexpressive edges and can be elongated. Diamonds (especially those with rounded crystal faces) are commonly found coated in ''nyf'', an opaque gum-like skin.<ref>{{cite book | vauthors = Webster R, Read PG |title=Gems: Their sources, descriptions and identification |edition=5th |page=17 |publisher=[[Butterworth-Heinemann]] |location=Great Britain |year=2000 |isbn=978-0-7506-1674-4}}</ref>

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.<ref name=Cartigny>{{cite journal | vauthors = Cartigny P, Palot M, Thomassot E, Harris JW |title=Diamond Formation: A Stable Isotope Perspective |journal=Annual Review of Earth and Planetary Sciences |date=May 30, 2014 |volume=42 |issue=1 |pages=699–732 |doi=10.1146/annurev-earth-042711-105259 |bibcode=2014AREPS..42..699C|doi-access=free }}</ref>

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.<ref name=Cartigny/> [[Carbonado]], a type in which the diamond grains were [[sintering|sintered]] (fused without melting by the application of heat and pressure), is black in color and tougher than single crystal diamond.<ref>{{cite journal | vauthors = Fukura S, Nakagawa T, Kagi H |title=High spatial resolution photoluminescence and Raman spectroscopic measurements of a natural polycrystalline diamond, carbonado |journal=Diamond and Related Materials |date=November 2005 |volume=14 |issue=11–12 |pages=1950–1954 |doi=10.1016/j.diamond.2005.08.046 |bibcode=2005DRM....14.1950F}}</ref> It has never been observed in a volcanic rock. There are many theories for its origin, including formation in a star, but no consensus.<ref name=Cartigny/><ref>{{cite journal | vauthors = Mohammad G, Siddiquei MM, Abu El-Asrar AM | title = Poly (ADP-ribose) polymerase mediates diabetes-induced retinal neuropathy | journal = Mediators of Inflammation | volume = 2013 | issue = 2 | article-number = 510451 | year = 2006 | pmid = 24347828 | doi = 10.1086/510451 | pmc = 3857786 | arxiv = physics/0608014 | s2cid = 59405368 | bibcode = 2006ApJ...653L.153G }}</ref><ref>{{cite web |title=Diamonds from Outer Space: Geologists Discover Origin of Earth's Mysterious Black Diamonds |url=https://www.nsf.gov/news/news_summ.jsp?cntn_id=108270&org=NSF |publisher=[[National Science Foundation]] |date=January 8, 2007 |access-date=October 28, 2007 |archive-date=December 9, 2007 |archive-url=https://web.archive.org/web/20071209203456/http://www.nsf.gov/news/news_summ.jsp?cntn_id=108270&org=NSF |url-status=live }}</ref>

=== Mechanical ===
==== Hardness ====
[[File:Vickers anvil diamons.jpg|thumb|The extreme hardness of diamond in certain orientations makes it useful in materials science, as in this pyramidal diamond embedded in the working surface of a [[Vickers hardness test]]er.]]
Diamond is the hardest material on the [[qualitative property|qualitative]] [[Mohs scale of mineral hardness|Mohs scale]]. To conduct the [[unit of measurement|quantitative]] [[Vickers hardness test]], samples of materials are struck with a pyramid of standardized dimensions using a known force – a diamond crystal is used for the pyramid to permit a wide range of materials to be tested. From the size of the resulting indentation, a Vickers hardness value for the material can be determined. 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.<ref>{{Cite web|date=December 16, 2015|title=Diamonds Are Indestructible, Right?|url=https://dominionjewelers.com/diamonds-are-indestructible-right/|access-date=October 31, 2020|website=Dominion Jewelers|language=en-US|archive-date=September 26, 2020|archive-url=https://web.archive.org/web/20200926001227/https://dominionjewelers.com/diamonds-are-indestructible-right/|url-status=live}}</ref> Indeed, diamonds can be scratched by other diamonds<ref>{{cite journal|vauthors=Seal M |title=The abrasion of diamond |journal=Proceedings of the Royal Society A |volume=248 |issue=1254 |date=November 25, 1958 |pages=379–393 |doi=10.1098/rspa.1958.0250|bibcode=1958RSPSA.248..379S }}</ref> and worn down over time even by softer materials, such as vinyl [[phonograph record]]s.<ref>{{cite web |vauthors=Weiler HD |title=The wear and care of records and styli |orig-date=1954 |date=April 13, 2021 |via=Shure Applications Engineering |url=https://service.shure.com/s/article/stylus-wear-and-record-wear?language=en_US |access-date=August 25, 2024 |archive-date=March 26, 2023 |archive-url=https://web.archive.org/web/20230326031532/https://service.shure.com/s/article/stylus-wear-and-record-wear?language=en_US |url-status=live }}</ref>

Diamond hardness depends on its purity, crystalline perfection, and orientation: hardness is higher for flawless, pure crystals oriented to the [[Miller index#Case of cubic structures|<111>]] direction (along the longest diagonal of the cubic diamond lattice).<ref>{{cite book|pages=142–147|url=https://books.google.com/books?id=jtC1mUFZfQcC&pg=PA143|title=Properties, Growth and Applications of Diamond|vauthors=Neves AJ, Nazaré MH|publisher=[[Institution of Engineering and Technology]]|year=2001|isbn=978-0-85296-785-0|access-date=November 9, 2020|archive-date=February 19, 2023|archive-url=https://web.archive.org/web/20230219072829/https://books.google.com/books?id=jtC1mUFZfQcC&pg=PA143|url-status=live}}</ref> Therefore, whereas it might be possible to scratch some diamonds with other materials, such as [[boron nitride]], the hardest diamonds can only be scratched by other diamonds and [[Aggregated diamond nanorod|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 ring|engagement]] or [[wedding ring]]s, which are often worn every day.

The hardest natural diamonds mostly originate from the [[Copeton Dam|Copeton]] and [[Bingara]] fields located in the [[New England (Australia)|New England]] area in [[New South Wales]], Australia. These diamonds are generally small, perfect to semiperfect octahedra, and are used to polish other diamonds. Their hardness is associated with the [[crystal growth]] form, which is single-stage crystal growth. Most other diamonds show more evidence of multiple growth stages, which produce inclusions, flaws, and defect planes in the crystal lattice, all of which affect their hardness. It is possible to treat regular diamonds under a combination of high pressure and high temperature to produce diamonds that are harder than the diamonds used in hardness gauges.<ref>{{cite magazine|vauthors=Boser U|title=Diamonds on Demand|url=http://www.smithsonianmag.com/science-nature/diamonds-on-demand.html|magazine=[[Smithsonian (magazine)|Smithsonian]]|volume=39|issue=3|pages=52–59|year=2008|access-date=June 13, 2009|archive-date=March 2, 2012|archive-url=https://web.archive.org/web/20120302163915/http://www.smithsonianmag.com/science-nature/diamonds-on-demand.html}}</ref>

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.<ref name=read/> 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;<ref name="hazen">{{cite book|url=https://books.google.com/books?id=fNJQok6N9_MC&pg=PA7|pages=7–10|title=The diamond makers| vauthors = Hazen RM |publisher=Cambridge University Press|year=1999|isbn=978-0-521-65474-6}}</ref> 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 [[diamantaire]]s still rely upon skilled use of a [[loupe]] (magnifying glass) to identify diamonds "by eye".<ref>{{cite book|url=https://books.google.com/books?id=Jm3FwBiHaI4C&pg=PA37|pages=34–37|title=Synthetic, Imitation and Treated Gemstones| vauthors = O'Donoghue M |publisher=Gulf Professional |year= 1997|isbn=978-0-7506-3173-0}}</ref>

==== Toughness ====
Somewhat related to hardness is another mechanical property ''toughness'', which is a material's ability to resist breakage from forceful impact. The [[toughness]] of natural diamond has been measured as 50–65&nbsp;[[Megapascal|MPa]]·m<sup>1/2</sup>.{{contradictory inline|reason=Unit of toughness as given at the article on toughness is newton-metres per cubic metre, dimensionally equivalent to newtons per square metre i.e. pascals. What is this factor of m^{1/2} doing here? Should we actually be talking about and linking to [[Fracture toughness]] (which unfortunately doesn't have a discussion of units)?|date=October 2023}}<ref>{{cite book| vauthors = Lee J, Novikov NV |title=Innovative superhard materials and sustainable coatings for advanced manufacturing|url=https://books.google.com/books?id=EXGcDYj8HvEC&pg=PA102|page=102|publisher=Springer|year=2005|isbn=978-0-8493-3512-9}}</ref><ref>{{cite book| vauthors = Marinescu ID, Tönshoff HK, Inasaki I |title=Handbook of ceramic grinding and polishing|url=https://books.google.com/books?id=QCvqtRJJ4XwC&pg=PA21|page=21|publisher=William Andrew|year=2000|isbn=978-0-8155-1424-4}}</ref> This value is good compared to other ceramic materials, but poor compared to most engineering materials such as engineering alloys, which typically exhibit toughness over 80{{nbsp}}MPa·m<sup>1/2</sup>. 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 cutting|Diamond cutters]] use this attribute to cleave some stones before faceting them.<ref name=harlow/> "Impact toughness" is one of the main indexes to measure the quality of synthetic industrial diamonds.

==== Yield strength ====
Diamond has compressive yield strength of 130–140{{nbsp}}GPa.<ref>{{cite journal | vauthors = Eremets MI, Trojan IA, Gwaze P, Huth J, Boehler R, Blank VD |title=The strength of diamond |journal=Applied Physics Letters |date=October 3, 2005 |volume=87 |issue=14 |article-number=141902 |doi=10.1063/1.2061853|bibcode=2005ApPhL..87n1902E}}</ref> This exceptionally high value, along with the hardness and transparency of diamond, are the reasons that [[diamond anvil]] cells are the main tool for high pressure experiments.<ref name=Dubrovinsky>{{cite journal | vauthors = Dubrovinsky L, Dubrovinskaia N, Prakapenka VB, Abakumov AM | title = Implementation of micro-ball nanodiamond anvils for high-pressure studies above 6 Mbar | journal = Nature Communications | volume = 3 | issue = 1 | article-number = 1163 | date = October 23, 2012 | pmid = 23093199 | pmc = 3493652 | doi = 10.1038/ncomms2160 | bibcode = 2012NatCo...3.1163D }}</ref> These anvils have reached pressures of {{val|600|u=GPa}}.<ref name="Wogan2012">{{Cite web |vauthors=Wogan T |publisher=Nature Communications |url=http://physicsworld.com/cws/article/news/2012/nov/02/improved-diamond-anvil-cell-allows-higher-pressures-than-ever-before |title=Improved diamond anvil cell allows higher pressures than ever before |work=[[Physics World]] |date=November 2, 2012 |access-date=July 1, 2022 |archive-date=January 2, 2018 |archive-url=https://web.archive.org/web/20180102123446/http://physicsworld.com/cws/article/news/2012/nov/02/improved-diamond-anvil-cell-allows-higher-pressures-than-ever-before |url-status=live }}</ref> Much higher pressures may be possible with [[nanocrystalline material|nanocrystalline]] diamonds.<ref name=Dubrovinsky/><ref name="Wogan2012"/>

==== Elasticity and tensile strength ====
Usually, attempting to deform bulk diamond crystal by tension or bending results in brittle fracture. However, when single crystalline diamond is in the form of micro/nanoscale wires or needles (~100–300{{nbsp}}nanometers in diameter, micrometers long), they can be elastically stretched by as much as 9–10 percent tensile strain without failure,<ref>{{cite journal | vauthors = Dang C, Chou JP, Dai B, Chou CT, Yang Y, Fan R, Lin W, Meng F, Hu A, Zhu J, Han J, Minor AM, Li J, Lu Y | display-authors = 6 | title = Achieving large uniform tensile elasticity in microfabricated diamond | journal = Science | volume = 371 | issue = 6524 | pages = 76–78 | date = January 2021 | pmid = 33384375 | doi = 10.1126/science.abc4174 | doi-access =  | bibcode = 2021Sci...371...76D | osti = 1755275 | s2cid = 229935085 }}</ref> with a maximum local tensile stress of about {{nowrap|89–98 GPa}},<ref>{{cite journal | vauthors = Banerjee A, Bernoulli D, Zhang H, Yuen MF, Liu J, Dong J, Ding F, Lu J, Dao M, Zhang W, Lu Y, Suresh S | display-authors = 6 | title = Ultralarge elastic deformation of nanoscale diamond | journal = Science | volume = 360 | issue = 6386 | pages = 300–302 | date = April 2018 | pmid = 29674589 | doi = 10.1126/science.aar4165 | doi-access =  | bibcode = 2018Sci...360..300B | s2cid = 5047604 }}</ref> very close to the theoretical limit for this material.<ref>{{cite journal | vauthors = LLorca J | title = On the quest for the strongest materials | journal = Science | volume = 360 | issue = 6386 | pages = 264–265 | date = April 2018 | pmid = 29674578 | doi = 10.1126/science.aat5211 | arxiv = 2105.05099 | s2cid = 4986592 | bibcode = 2018Sci...360..264L }}</ref>

=== Electrical conductivity ===
Other specialized applications also exist or are being developed, including use as [[semiconductor]]s: some [[blue diamond]]s are natural semiconductors, in contrast to most diamonds, which are excellent [[insulator (electricity)|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]].<ref name="boron">{{cite journal | vauthors = Collins AT |title=The Optical and Electronic Properties of Semiconducting Diamond |journal=[[Philosophical Transactions of the Royal Society A]] |volume=342 |pages=233–244 |year=1993 |doi=10.1098/rsta.1993.0017 |issue=1664 |bibcode=1993RSPTA.342..233C |s2cid=202574625}}</ref>

Substantial conductivity is commonly observed in nominally [[doping (semiconductor)|undoped]] diamond grown by [[chemical vapor deposition of diamond|chemical vapor deposition]]. This conductivity is associated with [[hydrogen]]-related species adsorbed at the surface, and it can be removed by [[annealing (metallurgy)|annealing]] or other surface treatments.<ref>{{cite journal | vauthors = Landstrass MI, Ravi KV |title=Resistivity of chemical vapor deposited diamond films |journal=[[Applied Physics Letters]] |volume=55 |pages=975–977 |year=1989 |doi=10.1063/1.101694 |issue=10 |bibcode=1989ApPhL..55..975L}}</ref><ref>{{cite journal | vauthors = Zhang W, Ristein J, Ley L | title = Hydrogen-terminated diamond electrodes. II. Redox activity | journal = Physical Review E | volume = 78 | issue = 4 Pt 1 | article-number = 041603 | date = October 2008 | pmid = 18999435 | doi = 10.1103/PhysRevE.78.041603 | bibcode = 2008PhRvE..78d1603Z }}</ref>

Thin needles of diamond can be made to vary their electronic [[band gap]] from the normal 5.6 eV to near zero by selective mechanical deformation.<ref>{{cite journal | vauthors = Shi Z, Dao M, Tsymbalov E, Shapeev A, Li J, Suresh S | title = Metallization of diamond | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 117 | issue = 40 | pages = 24634–24639 | date = October 2020 | pmid = 33020306 | pmc = 7547227 | doi = 10.1073/pnas.2013565117 | doi-access = free | bibcode = 2020PNAS..11724634S }}</ref>

High-purity diamond wafers 5&nbsp;cm in diameter exhibit perfect resistance in one direction and perfect conductance in the other, creating the possibility of using them for quantum data storage. The material contains only 3 parts per million of nitrogen. The diamond was grown on a stepped substrate, which eliminated cracking.<ref>{{Cite web | vauthors = Irving M |date=April 28, 2022 |title=Two-inch diamond wafers could store a billion Blu-Ray's worth of data |url=https://newatlas.com/electronics/2-inch-diamond-wafers-quantum-memory-billion-blu-rays/ |access-date=April 29, 2022 |website=New Atlas |language=en-US}}</ref>

=== Surface property ===
Diamonds are naturally [[lipophilicity|lipophilic]] and [[hydrophobe|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 [[hydrophile|hydrophilic]] that they can stabilize multiple layers of [[ice|water ice]] at [[human body temperature]].<ref>{{cite journal | vauthors = Wissner-Gross AD, Kaxiras E | title = Diamond stabilization of ice multilayers at human body temperature | journal = Physical Review E | volume = 76 | issue = 2 Pt 1 | article-number = 020501 | date = August 2007 | pmid = 17929997 | doi = 10.1103/physreve.76.020501 | url = http://www.alexwg.org/link?url=http%3A%2F%2Fwww.alexwg.org%2Fpublications%2FPhysRevERapidComm_76-020501.pdf | url-status = live | s2cid = 44344503 | bibcode = 2007PhRvE..76b0501W | archive-url = https://web.archive.org/web/20110724214405/http://www.alexwg.org/publications/PhysRevERapidComm_76-020501.pdf | archive-date = July 24, 2011 }}</ref>

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 (sp<sup>3</sup>C) are unstable against high temperature (above about {{convert|400|C}}) under atmospheric pressure. The structure gradually changes into sp<sup>2</sup>C above this temperature. Thus, diamonds should be reduced below this temperature.<ref>{{cite journal | vauthors = Fujimoto A, Yamada Y, Koinuma M, Sato S | title = Origins of sp(3)C peaks in C1s X-ray Photoelectron Spectra of Carbon Materials | journal = Analytical Chemistry | volume = 88 | issue = 12 | pages = 6110–6114 | date = June 2016 | pmid = 27264720 | doi = 10.1021/acs.analchem.6b01327 | doi-access = free }}</ref>

=== 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 {{convert|690|C}} to {{convert|840|C}}; 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.<ref>{{cite book | vauthors = Bauer M |title=Precious Stones | volume = 1 |date=2012 |publisher=Dover Publications |isbn=978-0-486-15125-0 |pages=115–117}}</ref> Heat generated from cutting a diamond will not ignite the diamond,<ref>{{cite web |title=Diamond Care and Cleaning Guide |url=https://www.gia.edu/diamond-care-cleaning |publisher=Gemological Institute of America |access-date=August 1, 2019 |language=en |archive-date=August 1, 2019 |archive-url=https://web.archive.org/web/20190801170616/https://www.gia.edu/diamond-care-cleaning |url-status=live }}</ref> and neither will a cigarette lighter,<ref>{{cite web |vauthors=Jones C |title=Diamonds are Flammable! How to Safeguard Your Jewelry |url=http://www.dmia.net/diamonds-are-flammable/ |website=DMIA |access-date=August 1, 2019 |date=August 27, 2016 |archive-date=August 1, 2019 |archive-url=https://web.archive.org/web/20190801170616/http://www.dmia.net/diamonds-are-flammable/ |url-status=live }}</ref> but house fires and blow torches are hot enough. Jewelers must be careful when molding the metal in a diamond ring.<ref>{{cite web |vauthors=Baird CS |title=Can you light diamond on fire? |url=https://wtamu.edu/~cbaird/sq/2014/03/27/can-you-light-diamond-on-fire/ |website=Science Questions with Surprising Answers |access-date=August 1, 2019 |archive-date=August 1, 2019 |archive-url=https://web.archive.org/web/20190801170618/https://wtamu.edu/~cbaird/sq/2014/03/27/can-you-light-diamond-on-fire/ |url-status=live }}</ref>

Diamond powder of an appropriate grain size (around 50{{nbsp}}microns) burns with a shower of sparks after ignition from a flame. Consequently, [[pyrotechnic composition]]s 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.<ref>{{cite journal| vauthors = Lederle F, Koch J, Hübner EG |title=Colored Sparks|journal=European Journal of Inorganic Chemistry|date=February 21, 2019|volume=2019|issue=7|pages=928–937|doi=10.1002/ejic.201801300|bibcode=2019EJIC.2019..928L |s2cid=104449284}}</ref> Diamond also reacts with fluorine gas above about {{convert|700|C}}.

=== Color ===
{{Main|Diamond color}}
[[File:National Museum of Natural History Gold Colored Diamonds.JPG|alt=A museum display of jewelry items. Three brooches each consist of a large brown central gem surrounded by many clear small stones. A necklace has a large brown gem at its bottom and its string is all covered with small clear gems. A cluster-shaped decoration contains many brown gems.|upright=1.35|thumb|Brown diamonds at the [[National Museum of Natural History]] in [[Washington, D.C.]]]]
[[File:The Hope Diamond - SIA.jpg|thumb|right|upright=1.35|alt=Picture of a diamond|The most famous colored diamond, the [[Hope Diamond]]]]
Diamond has a wide [[band gap]] of {{val|5.5|ul=eV}} corresponding to the deep [[ultraviolet]] wavelength of 225{{nbsp}}nanometers. This means that pure diamond should transmit visible light and appear as a clear colorless crystal. Colors in diamond originate from lattice defects and impurities. The diamond crystal lattice is exceptionally strong, and only atoms of [[nitrogen]], [[boron]], and [[hydrogen]] can be introduced into diamond during the growth at significant concentrations (up to atomic percents). Transition metals [[nickel]] and [[cobalt]], which are commonly used for growth of synthetic diamond by high-pressure high-temperature techniques, have been detected in diamond as individual atoms; the maximum concentration is 0.01% for nickel<ref>{{cite journal | vauthors = Collins AT, Kanda H, Isoya J, Ammerlaan CA, Van Wyk JA |title=Correlation between optical absorption and EPR in high-pressure diamond grown from a nickel solvent catalyst |journal=Diamond and Related Materials |volume=7 |pages=333–338 |year=1998 |doi=10.1016/S0925-9635(97)00270-7 |issue=2–5 |bibcode=1998DRM.....7..333C }}</ref> and even less for cobalt. Virtually any element can be introduced to diamond by ion implantation.<ref>{{cite journal |doi=10.1103/PhysRevB.61.12909 |title=Vibronic spectra of impurity-related optical centers in diamond |year=2000 | vauthors = Zaitsev AM |journal=Physical Review B |volume=61 |pages=12909–12922 |issue=19 |bibcode=2000PhRvB..6112909Z}}</ref>

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.<ref>{{cite journal| vauthors = Walker J |title=Optical absorption and luminescence in diamond|journal=Reports on Progress in Physics|volume=42|pages=1605–1659|year=1979|doi=10.1088/0034-4885/42/10/001|issue=10|bibcode=1979RPPh...42.1605W|url=http://accreditedgemologists.org/lightingtaskforce/OpticalAbsorptionand.pdf |archive-url=https://web.archive.org/web/20150906142645/http://accreditedgemologists.org/lightingtaskforce/OpticalAbsorptionand.pdf |archive-date=September 6, 2015 |url-status=live|citeseerx=10.1.1.467.443|s2cid=250857323 }}</ref> Color in diamond has two additional sources: irradiation (usually by alpha particles), that causes the color in green diamonds, and [[plastic deformation]] of the diamond crystal lattice. Plastic deformation is the cause of color in some brown<ref>{{cite journal| vauthors = Hounsome LS, Jones R, Shaw MJ, Briddon PR, Öberg S, Briddon P, Öberg S |title=Origin of brown coloration in diamond |journal=[[Physical Review B]] |volume=73 |article-number=125203|year=2006|doi=10.1103/PhysRevB.73.125203 |issue=12|bibcode=2006PhRvB..73l5203H}}</ref> and perhaps pink and red diamonds.<ref>{{cite book| vauthors = Wise RW |title=Secrets Of The Gem Trade, The Connoisseur's Guide To Precious Gemstones|publisher=Brunswick House Press|pages=223–224|year=2001|isbn=978-0-9728223-8-1}}</ref> In order of increasing rarity, yellow diamond is followed by brown, colorless, then by blue, green, black, pink, orange, purple, and red.<ref name=harlow/> "Black", or [[carbonado]], diamonds are not truly black, but rather contain numerous dark inclusions that give the gems their dark appearance. Colored diamonds contain impurities or structural defects that cause the coloration, while pure or nearly pure diamonds are transparent and colorless. Most diamond impurities replace a carbon atom in the [[crystal lattice]], known as a [[carbon flaw]]. The most common impurity, nitrogen, causes a slight to intense yellow coloration depending upon the type and concentration of nitrogen present.<ref name=harlow/> 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.<ref name=harlow/>

In 2008, the [[Wittelsbach Diamond]], a {{convert|35.56|carat|g|adj=on}} [[blue diamond]] once belonging to the King of Spain, fetched over US$24&nbsp;million at a Christie's auction.<ref>{{cite news |vauthors=Khan U |title=Blue-grey diamond belonging to King of Spain has sold for record 16.3{{nbsp}}GBP |url=https://www.telegraph.co.uk/culture/3703861/Blue-grey-diamond-belonging-to-King-of-Spain-has-sold-for-record-16.3m.html |work=[[The Daily Telegraph]] |location=London |date=December 10, 2008 |access-date=March 31, 2010 |archive-date=February 7, 2009 |archive-url=https://web.archive.org/web/20090207212758/http://www.telegraph.co.uk/culture/3703861/Blue-grey-diamond-belonging-to-King-of-Spain-has-sold-for-record-16.3m.html |url-status=live }}</ref> In May 2009, a {{convert|7.03|carat|g|adj=on}} [[blue diamond]] fetched the highest price per carat ever paid for a diamond when it was sold at auction for 10.5&nbsp;million Swiss francs (6.97&nbsp;million euros, or US$9.5&nbsp;million at the time).<ref>{{cite news|vauthors=Nebehay S|title=Rare blue diamond sells for record $9.5&nbsp;million|url=https://www.reuters.com/article/artsNews/idUSTRE54B6O020090512|work=Reuters|date=May 12, 2009|access-date=May 13, 2009|archive-date=May 16, 2009|archive-url=https://web.archive.org/web/20090516234031/http://www.reuters.com/article/artsNews/idUSTRE54B6O020090512|url-status=live}}</ref> That record was, however, beaten the same year: a {{convert|5|carat|g|adj=on}} vivid pink diamond was sold for US$10.8&nbsp;million in Hong Kong on December 1, 2009.<ref>{{cite news|url=https://www.reuters.com/article/idUSTRE5B02P620091201|title=Vivid pink diamond sells for record $10.8&nbsp;million|work=Reuters|date=December 1, 2009|vauthors=Pomfret J|access-date=July 1, 2017|archive-date=December 2, 2020|archive-url=https://web.archive.org/web/20201202103252/https://www.reuters.com/article/idUSTRE5B02P620091201|url-status=live}}</ref>

=== Clarity ===
Clarity is one of the 4C's (color, clarity, cut and carat weight) that helps in identifying the quality of diamonds. The [[Gemological Institute of America]] (GIA) developed 11 clarity scales to decide the quality of a diamond for its sale value. The GIA clarity scale spans from Flawless (FL) to included (I) having internally flawless (IF), very, very slightly included (VVS), very slightly included (VS) and slightly included (SI) in between. Impurities in natural diamonds are due to the presence of natural minerals and oxides. The clarity scale grades the diamond based on the color, size, location of impurity and quantity of clarity visible under 10x magnification.<ref>{{cite journal | vauthors = Cowing MD |year=2014 |title=Objective ciamond clarity grading |journal=Journal of Gemmology |volume=34 |number=4 |pages=316–332 |doi=10.15506/JoG.2014.34.4.316 |bibcode=2014JGem...34..316C |url=https://acagemlab.com/wp-content/uploads/2019/01/JoG2014_34_4_Cowing_Obj_Diamond_Clarity-1.pdf |archive-url=https://web.archive.org/web/20210418052002/https://acagemlab.com/wp-content/uploads/2019/01/JoG2014_34_4_Cowing_Obj_Diamond_Clarity-1.pdf |archive-date=April 18, 2021 |url-status=live |access-date=September 19, 2021}}</ref> 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.<ref>{{cite journal | vauthors = Wang W, Cai L | title = Inclusion extraction from diamond clarity images based on the analysis of diamond optical properties | journal = Optics Express | volume = 27 | issue = 19 | pages = 27242–27255 | date = September 2019 | pmid = 31674589 | doi = 10.1364/OE.27.027242 | bibcode = 2019OExpr..2727242W | s2cid = 203141270 | doi-access = free }}</ref>

=== Fluorescence ===
[[File:Rough diamonds - necklace in UV and normal light B - composite.jpg|thumb|Necklace of rough light brown diamonds under [[Blacklight|UV light]] (top) and normal light (bottom)]]
Between 25% and 35% of natural diamonds exhibit some degree of fluorescence when examined under invisible long-wave ultraviolet light or higher energy radiation sources such as X-rays and lasers.<ref>{{Cite web |date=March 27, 2018 |title=Fact Checking Diamond Fluorescence: 11 Myths Dispelled |url=https://4cs.gia.edu/en-us/blog/fact-checking-diamond-fluorescence-myths-dispelled/ |access-date=June 6, 2022 |website=GIA 4Cs |language=en-US |archive-date=March 24, 2022 |archive-url=https://web.archive.org/web/20220324052612/https://4cs.gia.edu/en-us/blog/fact-checking-diamond-fluorescence-myths-dispelled/ |url-status=live }}</ref> Incandescent lighting will not cause a diamond to fluoresce. Diamonds can fluoresce in a variety of colors including blue (most common), orange, yellow, white, green and very rarely red and purple. Although the causes are not well understood, variations in the atomic structure, such as the number of nitrogen atoms present are thought to contribute to the phenomenon.

=== Thermal conductivity ===
Diamonds can be identified by their high thermal conductivity (900–{{val|2320|u=W·m{{Sup|−1}}·K{{Sup|−1}}}}).<ref>{{cite journal | vauthors = Wei L, Kuo PK, Thomas RL, Anthony TR, Banholzer WF | title = Thermal conductivity of isotopically modified single crystal diamond | journal = Physical Review Letters | volume = 70 | issue = 24 | pages = 3764–3767 | date = June 1993 | pmid = 10053956 | doi = 10.1103/PhysRevLett.70.3764 | bibcode = 1993PhRvL..70.3764W }}</ref> Their high [[refractive index]] is also indicative, but other materials have similar refractivity.

== Geology ==
Diamonds are extremely rare, with concentrations of at most parts per billion in source rock.<ref name=Cartigny/> Before the 20th century, most diamonds were found in [[alluvial deposit]]s. Loose diamonds are also found along existing and ancient [[shore]]lines, where they tend to accumulate because of their size and density.<ref name=AMNH>{{cite book| vauthors = Erlich EI, Hausel WD |title=Diamond deposits: origin, exploration, and history of discovery|date=2002|publisher=Society for Mining, Metallurgy, and Exploration|location=Littleton, CO|isbn=978-0-87335-213-0}}</ref>{{rp|149}} Rarely, they have been found in [[glacial till]] (notably in [[Wisconsin]] and [[Indiana]]), but these deposits are not of commercial quality.<ref name=AMNH/>{{rp|19}} These types of deposit were derived from localized igneous [[intrusive rock|intrusions]] through [[weathering]] and [[sediment transport|transport]] by [[wind]] or [[water]].<ref name=Shirey2013>{{cite journal | vauthors = Shirey SB, Shigley JE |title=Recent Advances in Understanding the Geology of Diamonds |journal=Gems & Gemology |date=December 1, 2013 |volume=49 |issue=4 |pages=188–222 |doi=10.5741/GEMS.49.4.188 |doi-access=free}}</ref>

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 [[terrane]]s, 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.<ref name=Shirey2013/> Impact-type microdiamonds can be used as an indicator of ancient impact craters.<ref>{{cite book|title=The Mantle and Core|vauthors=Carlson RW|url=https://books.google.com/books?id=1clZ4ABsfoAC&pg=PA248|page=248|publisher=Elsevier|year=2005|isbn=978-0-08-044848-0|access-date=November 9, 2020|archive-date=November 9, 2023|archive-url=https://web.archive.org/web/20231109173351/https://books.google.com/books?id=1clZ4ABsfoAC&pg=PA248#v=onepage&q&f=false|url-status=live}}</ref> [[Popigai impact structure]] in Russia may have the world's largest diamond deposit, estimated at trillions of carats, and formed by an asteroid impact.<ref>{{Cite journal|volume=23|pages=3–12| vauthors = Deutsch A, Masaitis VL, Langenhorst F, Grieve RA |title=Popigai, Siberia—well preserved giant impact structure, national treasury, and world's geological heritage|journal=Episodes|year=2000|issue=1|doi=10.18814/epiiugs/2000/v23i1/002|doi-access=free}}</ref>

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 zone]]s, 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.<ref>{{cite web |url=http://geology.com/articles/diamonds-from-coal/ |title=How do diamonds form? They don't form from coal! | vauthors = King H |date=2012 |work=Geology and Earth Science News and Information |publisher=geology.com |access-date=June 29, 2012 |archive-url=https://web.archive.org/web/20131030014537/http://geology.com/articles/diamonds-from-coal/ |archive-date=October 30, 2013 |url-status=live}}</ref><ref>{{cite journal |title=10 common scientific misconceptions |vauthors=Pak-Harvey A |journal=The Christian Science Monitor |date=October 31, 2013 |url=https://www.csmonitor.com/Science/2013/1031/10-common-scientific-misconceptions/Diamonds-form-from-pressurized-coal |access-date=August 30, 2017 |archive-date=January 6, 2017 |archive-url=https://web.archive.org/web/20170106012033/http://www.csmonitor.com/Science/2013/1031/10-common-scientific-misconceptions/Diamonds-form-from-pressurized-coal |url-status=live }}</ref>

=== Surface distribution ===
[[File:World geologic provinces.jpg|thumb|[[Geologic province]]s of the world. The pink and orange areas are [[Shield (geology)|shields]] and [[Platform (geology)|platforms]], which together constitute cratons.]]

Diamonds are far from evenly distributed over the Earth. A rule of thumb known as Clifford's rule states that they are almost always found in [[kimberlite]]s on the oldest part of [[craton]]s, the stable cores of continents with typical ages of 2.5{{nbsp}}billion years or more.<ref name=Shirey2013/><ref>{{cite book | vauthors = Pohl WL |title=Economic Geology: Principles and Practice |date=2011 |publisher=John Wiley & Sons |isbn=978-1-4443-9486-3}}</ref>{{rp |314}} However, there are exceptions. The [[Argyle diamond mine]] in [[Australia]], the largest producer of diamonds by weight in the world, is located in a ''mobile belt'', also known as an ''[[orogeny|orogenic belt]]'',<ref>{{cite encyclopedia | vauthors = Allaby M |title=mobile belt |encyclopedia=A dictionary of geology and earth sciences |date=2013 |publisher=Oxford University Press |location=Oxford |isbn=978-0-19-174433-4 |edition=4th}}</ref> 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.<ref name=Shirey2013/> In addition, diamonds in the [[Algoman orogeny|Wawa belt]] of the [[Superior craton|Superior province]] in [[Canada]] and microdiamonds in the [[Northeastern Japan arc|island arc of Japan]] are found in a type of rock called [[lamprophyre]].<ref name=Shirey2013/>

[[Kimberlite]]s 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&nbsp;km. Fresh rock is dark bluish green to greenish gray, but after exposure rapidly turns brown and crumbles.<ref>{{cite book| vauthors = Kjarsgaard BA |chapter=Kimberlite pipe models: significance for exploration| veditors = Milkereit B |title=Proceedings of Exploration 07: Fifth Decennial International Conference on Mineral Exploration|date=2007|publisher=[[Decennial Mineral Exploration Conferences]], 2007|pages=667–677|chapter-url=http://www.dmec.ca/ex07-dvd/E07/pdfs/46.pdf |archive-url=https://web.archive.org/web/20121224053731/http://www.dmec.ca/ex07-dvd/E07/pdfs/46.pdf |archive-date=December 24, 2012 |url-status=live|access-date=March 1, 2018}}</ref> 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 [[xenocryst]]s and [[xenolith]]s (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 [[carbonatite]]s, but the latter have too much oxygen for carbon to exist in a pure form. Instead, it is locked up in the mineral [[calcite]] ({{chem|[[Calcium|Ca]]|[[Carbon|C]]|[[Oxygen|O]]|3}}).<ref name=Shirey2013/>

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.<ref name=Shirey2013/>

=== Exploration ===
[[File:Diavik Mine.tif|thumb|upright|[[Diavik Mine]], on an island in Lac de Gras in northern Canada]]

[[Kimberlite]] pipes can be difficult to find. They weather quickly (within a few years after exposure) and tend to have lower topographic relief than surrounding rock. If they are visible in outcrops, the diamonds are never visible because they are so rare. In any case, kimberlites are often covered with vegetation, sediments, soils, or lakes. In modern searches, [[geophysical survey|geophysical methods]] such as [[aeromagnetic survey]]s, [[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 [[eclogite]]s. 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.<ref name=Shirey2013/>

Finding kimberlites requires persistence, and only a small fraction contain diamonds that are commercially viable. The only major discoveries since about 1980 have been in Canada. Since existing mines have lifetimes of as little as 25 years, there could be a shortage of new natural diamonds in the future.<ref name=Shirey2013/>

=== 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 {{nowrap|1 to 3.5 billion years}}, and there can be multiple ages in the same kimberlite, indicating multiple episodes of diamond formation. The kimberlites themselves are much younger. Most of them have ages between tens of millions and 300 million years old, although there are some older exceptions (Argyle, [[Premier Mine|Premier]] and Wawa). Thus, the kimberlites formed independently of the diamonds and served only to transport them to the surface.<ref name=Cartigny/><ref name=Shirey2013/> 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.<ref name=Shirey2013/>

=== Origin in mantle ===
[[File:Eclogite, détail de la roche.jpg|thumb|[[Eclogite]] with centimeter-size [[garnet]] crystals]]
[[File:Garnet inclusion in diamond.jpg|thumb|Red garnet inclusion in a diamond<ref name=DCOdecadal>{{cite book |last1=Deep Carbon Observatory |title=Deep Carbon Observatory: A Decade of Discovery |doi=10.17863/CAM.44064 |date=2019 |publisher=Deep Carbon Observatory Secretariat |location=Washington, DC |url=https://deepcarbon.net/deep-carbon-observatory-decade-discovery |access-date=December 13, 2019 |archive-date=December 17, 2019 |archive-url=https://web.archive.org/web/20191217174901/https://deepcarbon.net/deep-carbon-observatory-decade-discovery }}</ref>]]
Most gem-quality diamonds come from depths of 150–250&nbsp;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.<ref name=Shirey2013/>

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]] 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.<ref name=Shirey2013/> 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]].<ref name=Cartigny/>

A smaller fraction of diamonds (about 150 have been studied) come from depths of 330–660&nbsp;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&nbsp;km.<ref name=Cartigny/>

Diamond is thermodynamically stable at high pressures and temperatures, with the phase transition from [[graphite]] occurring at greater temperatures as the pressure increases. Thus, underneath continents it becomes stable at temperatures of 950{{nbsp}}degrees Celsius and pressures of 4.5 gigapascals, corresponding to depths of 150{{nbsp}}kilometers or greater. In subduction zones, which are colder, it becomes stable at temperatures of 800&nbsp;°C and pressures of 3.5{{nbsp}}gigapascals. At depths greater than 240&nbsp;km, iron–nickel metal phases are present and carbon is likely to be either dissolved in them or in the form of [[carbide]]s. Thus, the deeper origin of some diamonds may reflect unusual growth environments.<ref name=Cartigny/><ref name=Shirey2013/>

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&nbsp;km, straddling the upper and lower mantle, and provide evidence for water-rich fluid at these depths.<ref>{{cite journal| vauthors = Cartier K |title=Diamond Impurities Reveal Water Deep Within the Mantle|journal=Eos|date=April 2, 2018|volume=99|doi=10.1029/2018EO095949|doi-access=free}}</ref><ref name=Perkins>{{cite journal|vauthors=Perkins S|title=Pockets of water may lie deep below Earth's surface|journal=Science|date=March 8, 2018|url=https://www.science.org/content/article/pockets-water-may-lay-deep-below-earth-s-surface|access-date=June 30, 2022|archive-date=March 8, 2018|archive-url=https://web.archive.org/web/20180308220310/http://www.sciencemag.org/news/2018/03/pockets-water-may-lay-deep-below-earth-s-surface|url-status=live}}</ref>

=== Carbon sources ===
The mantle has roughly one billion [[tonne|gigatonnes]] of carbon (for comparison, the atmosphere-ocean system has about 44,000 gigatonnes).<ref>{{cite book | vauthors = Lee CA, Jiang H, Dasgupta R, Torres M  |chapter=A Framework for Understanding Whole-Earth Carbon Cycling |pages=313–357 |doi=10.1017/9781108677950.011 | veditors = Orcutt BN, Daniel I, Dasgupta R |title=Deep carbon: past to present |date=2019 |publisher=Cambridge University Press |isbn=978-1-108-67795-0|s2cid=210787128 }}</ref> Carbon has two [[stable nuclide|stable isotopes]], [[carbon-12|<sup>12</sup>C]] and [[carbon-13|<sup>13</sup>C]], in a ratio of approximately 99:1 by mass.<ref name=Shirey2013/> 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|δ<sup>13</sup>C]] 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.<ref name=Cartigny/>

Populations of diamonds from different sources have distributions of δ<sup>13</sup>C 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.<ref name=Shirey2013/> Diamond-forming carbon originates in the top 700 kilometers (430&nbsp;mi) or so of the upper mantle closest to the surface, known as the [[asthenosphere]].<ref name=Cartigny/>

=== Formation and growth ===
[[File:Diamond age zones.jpg|thumb|Age zones in a diamond<ref name=DCOdecadal/>]]
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., CO<sub>2</sub> or CO<sub>3</sub>) or oxidation of a reduced phase such as [[methane]].<ref name=Cartigny/>

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.<ref name=Shirey2013/>

=== Transport to the surface ===
[[File:VolcanicPipe.jpg|thumb|upright=1.2|Diagram of a volcanic pipe]]
Geological evidence supports a model in which kimberlite magma rises at 4–20 meters per second, creating an upward path by [[hydraulic fracturing]] of the rock. As the pressure decreases, a vapor phase [[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 {{cvt|200|m/s|mph}}). Then, at lower pressures, the rock is eroded, forming a pipe and producing fragmented rock ([[breccia]]). As the eruption wanes, there is [[Pyroclastic rock|pyroclastic]] phase and then metamorphism and hydration produces [[serpentinite]]s.<ref name=Shirey2013/>

=== 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 [[Sakha Republic|Yakutia]], Russia, in 2019.<ref>{{cite web|url=https://www.nationalgeographic.com/science/article/rare-diamond-diamond-found-siberia|title=Bizarre 'nesting doll' diamond found inside another diamond|publisher=[[National Geographic]]|vauthors=Wei-Haas M|date=October 10, 2019|access-date=November 27, 2021|archive-date=November 27, 2021|archive-url=https://web.archive.org/web/20211127050127/https://www.nationalgeographic.com/science/article/rare-diamond-diamond-found-siberia}}</ref> Another one was found in the [[Ellendale Diamond Field]] in [[Western Australia]] in 2021.<ref>{{cite news|url=https://www.abc.net.au/news/2021-11-26/ellendale-discovery-comes-as-race-to-restart-production-heats-up/100648088|title=Rare 'double diamond' discovery comes as race to restart mothballed Ellendale mine heats up|publisher=[[Australian Broadcasting Corporation]]|vauthors=Fowler C|date=November 26, 2021|access-date=November 27, 2021|archive-date=November 26, 2021|archive-url=https://web.archive.org/web/20211126223633/https://www.abc.net.au/news/2021-11-26/ellendale-discovery-comes-as-race-to-restart-production-heats-up/100648088|url-status=live}}</ref>

=== In space ===
{{Main|Extraterrestrial diamonds}}
Although diamonds on [[Earth]] are rare, they are very common in space. In [[meteorite]]s, about three percent of the carbon is in the form of [[nanodiamond]]s, 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.<ref>{{cite journal| vauthors = Tielens AG |title=The molecular universe|journal=Reviews of Modern Physics|date=July 12, 2013|volume=85|issue=3|pages=1021–1081|doi=10.1103/RevModPhys.85.1021|bibcode=2013RvMP...85.1021T}}</ref>

High pressure experiments predict that large quantities of diamonds condense from [[methane]] into a "diamond rain" on the ice giant planets [[Uranus]] and [[Neptune]].<ref>{{cite journal | vauthors = Kerr RA | title = Neptune may crush methane into diamonds | journal = Science | volume = 286 | issue = 5437 | page = 25 | date = October 1999 | pmid = 10532884 | doi = 10.1126/science.286.5437.25a | s2cid = 42814647 }}</ref><ref>{{cite journal| vauthors = Scandolo S, Jeanloz R |author-link2=Raymond Jeanloz |title=The Centers of Planets: In laboratories and computers, shocked and squeezed matter turns metallic, coughs up diamonds and reveals Earth's white-hot center|journal=American Scientist|date=November–December 2003|volume=91|issue=6|pages=516–525|jstor=27858301|bibcode=2003AmSci..91..516S|doi=10.1511/2003.38.905|s2cid=120975663 }}</ref><ref>{{cite news |vauthors=Kaplan S |title=It rains solid diamonds on Uranus and Neptune |url=https://www.washingtonpost.com/news/speaking-of-science/wp/2017/08/25/it-rains-solid-diamonds-on-uranus-and-neptune/ |access-date=October 16, 2017 |newspaper=[[The Washington Post]] |date=August 25, 2017 |archive-date=August 27, 2017 |archive-url=https://web.archive.org/web/20170827011901/https://www.washingtonpost.com/news/speaking-of-science/wp/2017/08/25/it-rains-solid-diamonds-on-uranus-and-neptune/ |url-status=live }}</ref> Some extrasolar planets may be almost entirely composed of diamond.<ref>{{cite news|last1=Max Planck Institute for Radio Astronomy|title=A planet made of diamond|url=http://www.astronomy.com/news/2011/08/a-planet-made-of-diamond|access-date=September 25, 2017|work=Astronomy magazine|date=August 25, 2011|archive-date=May 14, 2023|archive-url=https://web.archive.org/web/20230514174530/https://astronomy.com/news/2011/08/a-planet-made-of-diamond|url-status=live}}</ref>

Diamonds may exist in carbon-rich stars, particularly [[white dwarf]]s. One theory for the origin of [[carbonado]], the toughest form of diamond, is that it originated in a white dwarf or [[supernova]].<ref>{{cite journal | vauthors = Heaney PJ, de Vicenzi EP |title=Strange Diamonds: the Mysterious Origins of Carbonado and Framesite |journal=Elements |volume=1 |pages=85–89 |year=2005 |doi=10.2113/gselements.1.2.85 |issue=2|bibcode=2005Eleme...1...85H }}</ref><ref>{{cite journal | vauthors = Shumilova T, Tkachev S, Isaenko S, Shevchuk S, Rappenglück M, Kazakov V |title=A "diamond-like star" in the lab. Diamond-like glass |journal=Carbon |date=April 2016 |volume=100 |pages=703–709 |doi=10.1016/j.carbon.2016.01.068|doi-access=free |bibcode=2016Carbo.100..703S }}</ref> Diamonds formed in stars may have been the first minerals.<ref>{{cite news |vauthors=Wei-Haas M |title=Life and Rocks May Have Co-Evolved on Earth |url=http://www.smithsonianmag.com/science-nature/life-and-rocks-may-have-co-evolved-on-earth-180957807/ |access-date=September 26, 2017 |work=[[Smithsonian (magazine)|Smithsonian]] |language=en |archive-date=September 2, 2017 |archive-url=https://web.archive.org/web/20170902203717/http://www.smithsonianmag.com/science-nature/life-and-rocks-may-have-co-evolved-on-earth-180957807/ |url-status=live }}</ref>

== Industry ==
{{See also|Diamonds as an investment|List of countries by diamond production|Clean Diamond Trade Act}}
[[File:Diamond.jpg|framed|alt=A clear faceted gem supported in four clamps attached to a wedding ring|A round [[Brilliant (diamond cut)|brilliant cut]] diamond set in a ring]]

The most familiar uses of diamonds today are as gemstones used for [[adornment]], and as industrial abrasives for cutting hard materials. The markets for gem-grade and industrial-grade diamonds value diamonds differently.

=== Gem-grade diamonds ===
{{Main|Diamond (gemstone)}}

The [[Dispersion (optics)|dispersion]] of white light into [[spectral color]]s 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 0.2{{nbsp}}grams), ''[[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]].<ref>{{cite book|url=https://books.google.com/books?id=DIWEi5Hg93gC&pg=PA42|page=42|vauthors=Hesse RW|title=Jewelrymaking through history|publisher=Greenwood Publishing Group|year=2007|isbn=978-0-313-33507-5|access-date=November 9, 2020|archive-date=November 9, 2023|archive-url=https://web.archive.org/web/20231109173258/https://books.google.com/books?id=DIWEi5Hg93gC&pg=PA42|url-status=live}}</ref>

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]].<ref>{{cite news| vauthors = Adiga A |title=Uncommon Brilliance |url=http://www.time.com/time/magazine/article/0,9171,501040419-610100,00.html|archive-url=https://web.archive.org/web/20070310173327/http://www.time.com/time/magazine/article/0,9171,501040419-610100,00.html|archive-date=March 10, 2007|magazine=[[Time (magazine)|Time]]|date=April 12, 2004|access-date=November 3, 2008}}</ref> 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 {{convert|12500000|and|15000000|carat|kg}} of diamonds per year<ref>{{cite web |title=Jwaneng|url=http://www.debswana.com/Operations/Pages/Jwaneng.aspx|publisher=Debswana|access-date=March 9, 2012|archive-url=https://web.archive.org/web/20120317175718/http://www.debswana.com/Operations/Pages/Jwaneng.aspx |archive-date=March 17, 2012}}</ref>).

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 diamond]]s, 50% of all cut diamonds and more than 50% of all rough, cut and industrial diamonds combined are handled.<ref name=India>{{cite book|vauthors=Tichotsky J|title=Russia's Diamond Colony: The Republic of Sakha|url=https://books.google.com/books?id=F7N4G_wxkUYC|page=254|publisher=[[Routledge]]|year=2000|isbn=978-90-5702-420-7|access-date=November 9, 2020|archive-date=November 9, 2023|archive-url=https://web.archive.org/web/20231109173259/https://books.google.com/books?id=F7N4G_wxkUYC|url-status=live}}</ref> This makes Antwerp a de facto "world diamond capital".<ref>{{cite news | url = http://www.spiegel.de/international/spiegel/0,1518,416243,00.html | title = Jews Surrender Gem Trade to Indians | work = [[Spiegel Online]] | date = May 15, 2006 | access-date = November 29, 2010 | archive-date = November 26, 2010 | archive-url = https://web.archive.org/web/20101126213945/http://www.spiegel.de/international/spiegel/0,1518,416243,00.html | url-status = live }}</ref> The city of Antwerp also hosts the [[Antwerpsche Diamantkring]], created in 1929 to become the first and biggest diamond bourse dedicated to rough diamonds.<ref>{{cite web |url=https://www.awdc.be/en/20th-century |title=The history of the Antwerp Diamond Center |website=Antwerp World Diamond Center |date=August 16, 2012 |access-date=June 30, 2015 |archive-date=February 22, 2013 |archive-url=https://web.archive.org/web/20130222071114/https://www.awdc.be/en/20th-century |url-status=live }}</ref> Another important diamond center is New York City, where almost 80% of the world's diamonds are sold, including auction sales.<ref name="India" />

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,<ref>{{cite web|url=http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CELEX:32003D0079:EN:HTML|title=Commission Decision of 25 July 2001 declaring a concentration to be compatible with the common market and the EEA Agreement|work=Case No COMP/M.2333 – De Beers/LVMH|publisher=[[EUR-Lex]]|year=2003|access-date=February 6, 2009|archive-date=May 12, 2011|archive-url=https://web.archive.org/web/20110512174536/http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CELEX:32003D0079:EN:HTML|url-status=live}}</ref> but by 2001–2009 the figure had decreased to around 45%,<ref>{{cite news |title=Business: Changing facets; Diamonds |url=https://www.economist.com/business/2007/02/22/changing-facets |newspaper=[[The Economist]] |volume=382 |issue=8517 |page=68 |year=2007 |access-date=December 22, 2010 |archive-date=May 12, 2011 |archive-url=https://web.archive.org/web/20110512061729/http://www.economist.com/node/8743058 |url-status=live }}</ref> and by 2013 the company's market share had further decreased to around 38% in value terms and even less by volume.<ref name="idexonline">{{cite web|url=http://www.idexonline.com/portal_FullEditorial.asp?id=38357|title=Certainty in the Diamond Industry? Watch Out For Tipping Points – IDEX's Memo|publisher=idexonline.com|access-date=September 24, 2014|archive-date=January 9, 2015|archive-url=https://web.archive.org/web/20150109023521/http://www.idexonline.com/portal_FullEditorial.asp?id=38357}}</ref> De Beers sold off the vast majority of its diamond stockpile in the late 1990s – early 2000s<ref>{{cite web|title=The Elusive Sparcle |url=http://www.gjepc.org/solitaire/magazines/Aug05_Sep05/aug05_sep05.aspx?inclpage=Specials&section_id=3 |publisher=The Gem & Jewellery Export Promotion Council |access-date=April 26, 2009 |archive-url=https://web.archive.org/web/20090616043101/http://www.gjepc.org/solitaire/magazines/Aug05_Sep05/aug05_sep05.aspx?inclpage=Specials&section_id=3 |archive-date=June 16, 2009 }}</ref> and the remainder largely represents working stock (diamonds that are being sorted before sale).<ref>{{cite news| vauthors = Even-Zohar C |title=Crisis Mitigation at De Beers|url=http://www.docstoc.com/docs/19770902/Crisis-Mitigation-at-De-Beers|publisher=DIB online|date=November 6, 2008|access-date=April 26, 2009|archive-url=https://web.archive.org/web/20110512061727/http://www.docstoc.com/docs/19770902/Crisis-Mitigation-at-De-Beers|archive-date=May 12, 2011}}</ref> This was well documented in the press<ref>{{cite web| vauthors = Even-Zohar C |title=De Beers to Halve Diamond Stockpile |url=http://www.allbusiness.com/retail-trade/apparel-accessory-stores-womens-specialty/4224156-1.html |publisher=[[Jewelers of America#National Jeweler|National Jeweler]] |date=November 3, 1999 |access-date=April 26, 2009 |archive-url=https://web.archive.org/web/20090705101028/http://www.allbusiness.com/retail-trade/apparel-accessory-stores-womens-specialty/4224156-1.html |archive-date=July 5, 2009 }}</ref> 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]].<ref>{{cite web|title=Judgment of the Court of First Instance of 11 July 2007 – Alrosa v Commission|url=http://eur-lex.europa.eu/legal-content/EN/ALL/?uri=CELEX:C2007/199/70|publisher=EUR-Lex|year=2007|access-date=April 26, 2009|archive-date=December 1, 2017|archive-url=https://web.archive.org/web/20171201043518/http://eur-lex.europa.eu/legal-content/EN/ALL/?uri=CELEX:C2007/199/70|url-status=live}}</ref> As of January 2011, De Beers states that it only sells diamonds from the following four countries: Botswana, Namibia, South Africa and Canada.<ref>{{cite web |url=http://www.debeersgroup.com/en/Exploration-and-mining/Mining-operations/ |title=Mining operations |publisher=The De Beers Group |year=2007 |access-date=January 4, 2011 |archive-url=https://web.archive.org/web/20080613143223/http://www.debeersgroup.com/en/Exploration-and-mining/Mining-operations/ |archive-date=June 13, 2008 }}</ref> Apart from Alrosa, other important diamond mining companies include [[BHP]], which is the world's largest mining company;<ref>{{cite news|url = http://www.abc.net.au/news/stories/2007/08/22/2012367.htm|title = Another record profit for BHP|publisher = ABC News|date = August 22, 2007|access-date = August 23, 2007|archive-date = May 12, 2011|archive-url = https://web.archive.org/web/20110512061741/http://www.abc.net.au/news/stories/2007/08/22/2012367.htm}}</ref> [[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;<ref>{{cite web|title=Our Companies|work=Rio Tinto web site|publisher=Rio Tinto|url=http://www.riotinto.com/whatweproduce/218_our_companies.asp|access-date=March 5, 2009|archive-url=https://web.archive.org/web/20130511045232/http://www.riotinto.com/whatweproduce/218_our_companies.asp|archive-date=May 11, 2013}}</ref> and [[Petra Diamonds]], the owner of several major diamond mines in Africa.

[[File:Diamond Polisher.jpg|thumb|right|Diamond polisher in Amsterdam]]

Further down the supply chain, members of The [[World Federation of Diamond Bourses]] (WFDB) act as a medium for wholesale diamond exchange, trading both polished and rough diamonds. The WFDB consists of independent diamond bourses in major cutting centers such as Tel Aviv, Antwerp, Johannesburg and other cities across the US, Europe and Asia.<ref name=harlow/> 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.<ref>{{Cite web |title=Introduction {{!}} IDC |url=https://internationaldiamondcouncil.org/introduction |access-date=October 18, 2022 |website=internationaldiamondcouncil.org |language=en |archive-date=October 18, 2022 |archive-url=https://web.archive.org/web/20221018144626/https://internationaldiamondcouncil.org/introduction |url-status=live }}</ref>

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).<ref name=polish>{{cite book | url = https://books.google.com/books?id=fkBJ0HL34WsC&pg=PA297 | pages = 297–299 | title = Africa's silk road | vauthors = Broadman HG, Isik G | publisher = World Bank Publications | year = 2007 | isbn = 978-0-8213-6835-0 | access-date = November 9, 2020 | archive-date = November 9, 2023 | archive-url = https://web.archive.org/web/20231109173401/https://books.google.com/books?id=fkBJ0HL34WsC&pg=PA297#v=onepage&q&f=false | url-status = live }}</ref> The cutting and polishing of rough diamonds is a specialized skill that is concentrated in a limited number of locations worldwide.<ref name=polish/> 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.<ref name=polish/> 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.<ref name="India" />

Diamonds prepared as gemstones are sold on diamond exchanges called ''[[Exchange (organized market)|bourses]]''. There are 28 registered diamond bourses in the world.<ref>{{cite web|title=Bourse listing|url=http://www.wfdb.com/wfdb-bourses|publisher=World Federation of Diamond Bourses|access-date=February 12, 2012|archive-date=October 25, 2016|archive-url=https://web.archive.org/web/20161025031428/http://wfdb.com/wfdb-bourses}}</ref> 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&nbsp;billion as rough diamonds, US$14&nbsp;billion after being cut and polished, US$28&nbsp;billion in wholesale diamond jewelry, and US$57&nbsp;billion in retail sales.<ref>{{cite web|title=North America Diamond Sales Show No Sign of Slowing |url=http://www.awdiamonds.com/article-8.html|publisher=A&W diamonds|access-date=May 5, 2009 |url-status=usurped |archive-url=https://web.archive.org/web/20090106185423/http://www.awdiamonds.com/article-8.html|archive-date=January 6, 2009}}</ref>

==== Cutting ====
{{Main|Diamond cutting|Diamond cut}}
[[File:The Daria-e Noor (Sea of Light) Diamond from the collection of the national jewels of Iran at Central Bank of Islamic Republic of Iran.jpg|thumb|right|alt=A large rectangular pink multifaceted gemstone, set in a decorative surround. The decoration includes a row of small clear faceted gemstones around the main gem's perimeter, and clusters of gems forming a crest on one side. The crest comprises a three-pointed crown faced by two unidentifiable animals.|The [[Daria-i-Noor]] Diamond—an example of unusual diamond cut and jewelry arrangement.]]

Mined rough diamonds are converted into gems through a multi-step process called "cutting". Diamonds are extremely hard, but also brittle and can be split up by a single blow. Therefore, diamond cutting is traditionally considered as a delicate procedure requiring skills, scientific knowledge, tools and experience. Its final goal is to produce a faceted jewel where the specific angles between the facets would optimize the diamond luster, that is dispersion of white light, whereas the number and area of facets would determine the weight of the final product. The weight reduction upon cutting is significant and can be of the order of 50%.<ref name=x50>{{cite book | url = https://books.google.com/books?id=jPT6JADCqgwC&pg=PA280 | page = 280 | title = Handbook of carbon, graphite, diamond, and fullerenes: properties, processing, and applications | vauthors = Pierson HO | publisher = William Andrew | year = 1993 | isbn = 978-0-8155-1339-1 }}</ref> 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.<ref name=antique>{{cite book | pages = 82–102 | title = Antique jewellery: its manufacture, materials and design | vauthors = James DS | publisher = Osprey Publishing | year = 1998 | isbn = 978-0-7478-0385-0  }}</ref> Some of them may be considered as classical, such as [[Diamond cut|round]], [[Pear Cut Diamond|pear]], [[Marquise Cut 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.<ref>{{cite web|url=http://www.kristallsmolensk.com/backstage/benchmarks/shapes/|title=The Classical and Special Shapes of Diamonds|publisher=kristallsmolensk.com|access-date=July 14, 2015|archive-date=July 14, 2015|archive-url=https://web.archive.org/web/20150714175156/http://www.kristallsmolensk.com/backstage/benchmarks/shapes/|url-status=live}}</ref>

The most time-consuming part of the cutting is the preliminary analysis of the rough stone. It needs to address a large number of issues, bears much responsibility, and therefore can last years in case of unique diamonds. The following issues are considered:
* The hardness of diamond and its ability to cleave strongly depend on the crystal orientation. Therefore, the crystallographic structure of the diamond to be cut is analyzed using [[X-ray diffraction]] to choose the optimal cutting directions.
* Most diamonds contain visible non-diamond inclusions and crystal flaws. The cutter has to decide which flaws are to be removed by the cutting and which could be kept.
* Splitting a diamond with a hammer is difficult, a well-calculated, angled blow can cut the diamond, piece-by-piece, but it can also ruin the diamond itself. Alternatively, it can be cut with a [[diamond saw]], which is a more reliable method.<ref name=antique/><ref>{{cite book | url = https://books.google.com/books?id=X3qe9jzYUAQC&pg=PA984 | pages = 984–992 | title = Handbook of industrial diamonds and diamond films | vauthors = Prelas MA, Popovici G, Bigelow LK | publisher = CRC Press | year = 1998 | isbn = 978-0-8247-9994-6 | access-date = November 9, 2020 | archive-date = November 9, 2023 | archive-url = https://web.archive.org/web/20231109173351/https://books.google.com/books?id=X3qe9jzYUAQC&pg=PA984#v=onepage&q&f=false | url-status = live }}</ref>

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.<ref>{{cite journal | url = https://books.google.com/books?id=i9kDAAAAMBAJ&pg=PA760 | pages = 760–764 | title = Gem Cutting | journal = [[Popular Mechanics]] | year = 1940 | volume = 74 | issue = 5 | issn = 0032-4558 | access-date = November 9, 2020 | archive-date = November 9, 2023 | archive-url = https://web.archive.org/web/20231109173258/https://books.google.com/books?id=i9kDAAAAMBAJ&pg=PA760#v=onepage&q&f=false | url-status = live }}</ref> 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.<ref name=read>{{cite book | url = https://books.google.com/books?id=t-OQO3Wk-JsC&pg=PA166 | pages = 165–166 | title = Gemmology | vauthors = Read PG | publisher = Butterworth-Heinemann | year = 2005 | isbn = 978-0-7506-6449-3 | access-date = November 9, 2020 | archive-date = November 9, 2023 | archive-url = https://web.archive.org/web/20231109173801/https://books.google.com/books?id=t-OQO3Wk-JsC&pg=PA166#v=onepage&q&f=false | url-status = live }}</ref>

==== Marketing ====
[[File:Diamond Balance Scale 0.01 - 25 Carats Jewelers Measuring Tool.jpg|thumb|Diamond balance scale 0.01–25 carat jeweler's measuring tool]]

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

[[N. W. Ayer & Son]], the advertising firm retained by [[De Beers]] in the mid-20th century, succeeded in reviving the American diamond market and the firm created new markets in countries where no diamond tradition had existed before. N. W. Ayer's marketing included [[product placement]], advertising focused on the diamond product itself rather than the De Beers brand, and associations with celebrities and royalty. Without advertising the De Beers brand, De Beers was advertising its competitors' diamond products as well,<ref>{{cite web | url = http://www.diamonds.net/news/NewsItem.aspx?ArticleID=33243 | title = Keep the Diamond Dream Alive | vauthors = Rapaport M | work = Rapaport Magazine | publisher = Diamonds.net | access-date = September 9, 2012 | archive-date = September 13, 2012 | archive-url = https://web.archive.org/web/20120913214013/http://www.diamonds.net/news/NewsItem.aspx?ArticleID=33243 | url-status = live }}</ref> but this was not a concern as De Beers dominated the diamond market throughout the 20th century. De Beers' market share dipped temporarily to second place in the global market below Alrosa in the aftermath of the global economic crisis of 2008, down to less than 29% in terms of carats mined, rather than sold.<ref name="jckonline.com">{{cite web |author=JCK Staff |url=http://www.jckonline.com/2011/01/26/10-things-rocking-industry |title=10 Things Rocking the Industry |work=JCK |publisher=Jckonline.com |date=January 26, 2011 |access-date=September 9, 2012 |archive-url=https://web.archive.org/web/20130107102249/http://www.jckonline.com/2011/01/26/10-things-rocking-industry |archive-date=January 7, 2013 }}</ref> 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.<ref name="jckonline.com"/> The campaign was perhaps best captured by the slogan "[[a diamond is forever]]".<ref name=sell /> This slogan is now being used by De Beers Diamond Jewelers,<ref>{{cite web | vauthors = Bates R |url=http://www.jckonline.com/blogs/cutting-remarks/2011/01/14/interview-forevermark-ceo |title=Interview with Forevermark CEO |work=JCK |publisher=Jckonline.com |date=January 14, 2011 |access-date=September 9, 2012 |archive-url=https://web.archive.org/web/20121128004942/http://www.jckonline.com/blogs/cutting-remarks/2011/01/14/interview-forevermark-ceo |archive-date=November 28, 2012 }}</ref> 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.<ref>{{cite book|url=https://books.google.com/books?id=_WI86J88ydAC&pg=PA34|page=34|title=The nature of diamonds| vauthors = Harlow GE |publisher=Cambridge University Press|year=1998|isbn=978-0-521-62935-5}}</ref><ref>{{cite book|url=https://books.google.com/books?id=zNicdkuulE4C&pg=PA416 |page=416|title=Industrial minerals & rocks| vauthors = Kogel JE |publisher= Society for Mining, Metallurgy, and Exploration (U.S.)|year=2006|isbn=978-0-87335-233-8}}</ref> The change was mostly due to the numbers: the Argyle mine, with its {{convert|35000000|carat|kg}} of diamonds per year, makes about one-third of global production of natural diamonds;<ref>{{cite web|access-date=August 4, 2009 |url=http://www.costellos.com.au/diamonds/industry.html |title=The Australian Diamond Industry |archive-url=https://web.archive.org/web/20090716170624/http://www.costellos.com.au/diamonds/industry.html |archive-date=July 16, 2009 }}</ref> 80% of Argyle diamonds are brown.<ref>{{cite book | url = https://books.google.com/books?id=068-M3xrDSQC&pg=PT158 | page = 158 | title = Diamond deposits: origin, exploration, and history of discovery | vauthors = Erlich E, Hausel DW | publisher = SME | year = 2002 | isbn = 978-0-87335-213-0 }}</ref>

=== Industrial-grade diamonds ===
[[File:Dia scalpel.jpg|thumb|alt=A diamond scalpel consisting of a yellow diamond blade attached to a pen-shaped holder|A [[scalpel]] with synthetic diamond blade]]
[[File:Diamond blade very macro.jpg|thumb|alt=A polished metal blade embedded with small diamonds|Close-up photograph of an [[angle grinder]] blade with tiny diamonds shown embedded in the metal]]
[[File:Diamond Knife Blade Edge.jpg|thumb|A diamond knife blade used for cutting ultrathin sections (typically 70 to 350&nbsp;nm) for transmission [[electron microscopy]]]]

Industrial diamonds are valued mostly for their hardness and thermal conductivity, making many of the gemological characteristics of diamonds, such as the [[4 Cs]], irrelevant for most applications. Eighty percent of mined diamonds (equal to about {{convert|135000000|carat|kg}} annually) are unsuitable for use as gemstones and are used industrially.<ref>{{cite web|url=http://www.minerals.net/mineral/diamond.aspx|title=Diamond: The mineral Diamond information and pictures|publisher=minerals.net|access-date=September 24, 2014|archive-date=October 23, 2014|archive-url=https://web.archive.org/web/20141023195127/http://www.minerals.net/mineral/diamond.aspx|url-status=live}}</ref> In addition to mined diamonds, synthetic diamonds found industrial applications almost immediately after their invention in the 1950s; in 2014, {{convert|4500000000|carat|kg}} of synthetic diamonds were produced, 90% of which were produced in China. Approximately 90% of diamond [[Grinding (abrasive cutting)|grinding grit]] is currently of synthetic origin.<ref name=usgs>{{cite web|title=Industrial Diamonds Statistics and Information|url=http://minerals.usgs.gov/minerals/pubs/commodity/diamond/|work=[[United States Geological Survey]]|access-date=May 5, 2009|archive-date=May 6, 2009|archive-url=https://web.archive.org/web/20090506221551/http://minerals.usgs.gov/minerals/pubs/commodity/diamond/|url-status=live}}</ref>

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]].<ref name=spear>{{cite book| vauthors = Spear KE, Dismukes JP |title=Synthetic Diamond: Emerging CVD Science and Technology|url=https://books.google.com/books?id=RR5HF25DB7UC|page=628|publisher=[[John Wiley & Sons|Wiley]]–[[IEEE]]|year=1994|isbn=978-0-471-53589-8}}</ref>

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 bit]]s and saws, and the use of diamond powder as an [[abrasive]]. Less expensive industrial-grade diamonds (bort) with more flaws and poorer color than gems, are used for such purposes.<ref>{{cite book| vauthors = Holtzapffel C |title=Turning And Mechanical Manipulation |url= https://archive.org/details/turningandmecha01holtgoog|publisher=Holtzapffel & Co |pages= [https://archive.org/details/turningandmecha01holtgoog/page/n192 176–178]|year=1846}}</ref> Diamond is not suitable for machining [[ferrous]] [[alloy]]s 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.<ref>{{cite journal| vauthors = Coelho RT, Yamada S, Aspinwall DK, Wise ML |title=The application of polycrystalline diamond (PCD) tool materials when drilling and reaming aluminum-based alloys including MMC|journal=International Journal of Machine Tools and Manufacture|volume=35|issue=5|pages=761–774|year=1995|doi=10.1016/0890-6955(95)93044-7}}</ref>

Specialized applications include use in laboratories as containment for [[Pressure experiment|high-pressure experiments]] (see [[diamond anvil cell]]), high-performance [[bearing (mechanical)|bearings]], and limited use in specialized [[window]]s.<ref name=spear/> With the continuing advances being made in the production of synthetic diamonds, future applications are becoming feasible. The high [[thermal conductivity]] of diamond makes it suitable as a [[heat sink]] for integrated circuits in [[electronics]].<ref>{{cite journal | vauthors = Sakamoto M, Endriz JG, Scifres DR |title=120&nbsp;W CW output power from monolithic AlGaAs (800&nbsp;nm) laser diode array mounted on diamond heatsink|journal=[[Electronics Letters]] |volume=28 |issue=2 |pages=197–199 |year=1992 |doi=10.1049/el:19920123 |bibcode=1992ElL....28..197S}}</ref>

=== Mining ===
{{See also|List of diamond mines|Exploration diamond drilling}}

Approximately {{convert|130000000|carat|kg}} of diamonds are mined annually, with a total value of nearly US$9&nbsp;billion, and about {{convert|100000|kg|abbr=on}} are synthesized annually.<ref name=yarnell>{{cite journal|vauthors=Yarnell A|title=The Many Facets of Man-Made Diamonds|url=http://pubs.acs.org/cen/coverstory/8205/8205diamonds.html|journal=[[Chemical and Engineering News]]|volume=82|issue=5|pages=26–31|year=2004|doi=10.1021/cen-v082n005.p026|access-date=October 3, 2006|archive-date=October 28, 2008|archive-url=https://web.archive.org/web/20081028181945/http://pubs.acs.org/cen/coverstory/8205//8205diamonds.html|url-status=live|url-access=subscription}}</ref>

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]].<ref name=usgs/> 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 diamond]]s'' or ''conflict diamonds'' by African [[paramilitary]] groups.<ref name=conflict>{{cite web|title=Conflict Diamonds |url=https://www.un.org/peace/africa/Diamond.html |publisher=United Nations |date=March 21, 2001 |access-date=May 5, 2009 |archive-url=https://web.archive.org/web/20100309083348/http://www.un.org/peace/africa/Diamond.html |archive-date=March 9, 2010 }}</ref> 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-ray]]s became commonplace,<ref name=x50/> the separation was done with grease belts; diamonds have a stronger tendency to stick to grease than the other minerals in the ore.<ref name=harlow>{{cite book| vauthors = Harlow GE |title=The nature of diamonds|pages=223, 230–249|url=https://books.google.com/books?id=_WI86J88ydAC&pg=PA223|publisher=[[Cambridge University Press]]|year=1998|isbn=978-0-521-62935-5}}</ref>

[[File:Udachnaya pipe.JPG|thumb|[[Siberia]]'s Udachnaya diamond mine]]
[[File:Diamond 4.jpg|thumb|The slightly misshapen octahedral shape of this rough diamond crystal in matrix is typical of the mineral. Its lustrous faces also indicate that this crystal is from a primary deposit|alt=A clear octahedral stone protrudes from a black rock]]

Historically, diamonds were found only in [[alluvial deposit]]s in [[Guntur district|Guntur]] and [[Krishna district]] of the [[Krishna River]] delta in [[Southern India]].<ref>{{cite book| vauthors = Catelle WR |title=The Diamond|publisher=John Lane Co.|year=1911|page=159}}</ref> India led the world in diamond production from the time of their discovery in approximately the 9th century BC<ref name=hershey/><ref>{{cite book| vauthors = Ball V |chapter=1|title=Diamonds, Gold and Coal of India|url=https://archive.org/details/diamondscoalgold00ballrich |page=[https://archive.org/details/diamondscoalgold00ballrich/page/n12 1]|publisher=Trübner & Co|location=London|year=1881}} Ball was a geologist in British service.</ref> 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.<ref name=hershey/> Currently, one of the most prominent Indian mines is located at [[Panna District|Panna]].<ref>{{cite news|url=http://www.9newz.com/mail-today-biggest-diamond-found-in-panna|title=Biggest diamond found in Panna|date=July 1, 2010|publisher=Mail Today|archive-url=https://web.archive.org/web/20110707071636/http://www.9newz.com/mail-today-biggest-diamond-found-in-panna|archive-date=July 7, 2011}}</ref>

Diamond extraction from primary deposits (kimberlites and lamproites) started in the 1870s after the discovery of the [[Diamond Fields]] in South Africa.<ref>{{cite book | title = Encyclopedia of African history | vauthors = Shillington K | page = 767 | url = https://books.google.com/books?id=Ftz_gtO-pngC&pg=PA767 | publisher = CRC Press | isbn = 978-1-57958-453-5 | year = 2005 | access-date = November 9, 2020 | archive-date = November 9, 2023 | archive-url = https://web.archive.org/web/20231109173804/https://books.google.com/books?id=Ftz_gtO-pngC&pg=PA767#v=onepage&q&f=false | url-status = live }}</ref> Production has increased over time and now an accumulated total of {{convert|4500000000|carat|kg}} have been mined since that date.<ref name=giasummer2007>{{cite journal| vauthors = Janse AJ |title=Global Rough Diamond Production Since 1870|journal=Gems & Gemology|volume=43|pages=98–119|year=2007|doi=10.5741/GEMS.43.2.98|issue=2|bibcode=2007GemG...43...98J }}</ref> 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.<ref name=giasummer2007/>

In the U.S., diamonds have been found in [[Arkansas]], [[Colorado]], [[New Mexico]], Wyoming, and [[Montana]].<ref name=DGemGLorenz>{{cite journal | vauthors = Lorenz V |title=Argyle in Western Australia: The world's richest diamantiferous pipe; its past and future |journal=Gemmologie, Zeitschrift der Deutschen Gemmologischen Gesellschaft |volume=56 |issue=1–2 |pages=35–40 |year=2007}}</ref><ref name=Montana>{{cite web |title=Microscopic diamond found in Montana |url=http://www.montanastandard.com/articles/2004/10/18/featuresbusiness/hjjfijicjbhdjc.txt | vauthors = Cooke S |work=[[The Montana Standard]] |date=October 17, 2004 |access-date=May 5, 2009 |archive-url=https://web.archive.org/web/20050121085707/http://www.montanastandard.com/articles/2004/10/18/featuresbusiness/hjjfijicjbhdjc.txt |archive-date=January 21, 2005}}</ref> In 2004, the discovery of a microscopic diamond in the U.S. led to the January 2008 bulk-sampling of [[kimberlite pipe]]s 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.<ref name=Montana/>

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]].<ref>{{cite web| vauthors = Marshall S, Shore J |title=The Diamond Life|url=http://gnn.tv/videos/2/The_Diamond_Life|publisher=[[Guerrilla News Network]]|year=2004|access-date=March 21, 2007|archive-url=https://web.archive.org/web/20070126235556/http://gnn.tv/videos/2/The_Diamond_Life|archive-date=January 26, 2007}}</ref> In 2005, Russia produced almost one-fifth of the global diamond output, according to the [[British Geological Survey]]. Australia boasts the richest diamantiferous pipe, with production from the Argyle diamond mine reaching peak levels of 42{{nbsp}}metric tons per year in the 1990s.<ref name=DGemGLorenz/><ref>{{cite journal| vauthors = Shigley JE, Chapman J, Ellison RK |year=2001|title=Discovery and Mining of the Argyle Diamond Deposit, Australia|journal=Gems & Gemology |volume=37|issue=1|pages=26–41 |url=http://www.argylediamonds.com.au/docs/gems_and_gemology.pdf|access-date=February 20, 2010|doi=10.5741/GEMS.37.1.26|bibcode=2001GemG...37...26S |archive-url=https://web.archive.org/web/20090930095856/http://www.argylediamonds.com.au/docs/gems_and_gemology.pdf|archive-date=September 30, 2009}}</ref> There are also commercial deposits being actively mined in the [[Northwest Territories]] of Canada and Brazil.<ref name=usgs/> Diamond prospectors continue to search the globe for diamond-bearing kimberlite and lamproite pipes.

==== Political issues ====
{{Main|Kimberley Process|Blood diamond|Child labour in the diamond industry}}
[[File:Unsustainable Growth.webm|thumb|Unsustainable diamond mining in Sierra Leone. Documentary as part of the Vrinda Project for Wikibooks]]

In some of the more politically unstable [[central Africa]]n and [[west Africa]]n 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''.<ref name=conflict/>

In response to public concerns that their diamond purchases were contributing to war and [[human rights abuses]], the [[United Nations]], the diamond industry and diamond-trading nations introduced the [[Kimberley Process]] in 2002.<ref name=kimb>{{cite book|url=https://books.google.com/books?id=hWrEcl2ydzEC&pg=PA305|pages=305–313|title=Resource politics in Sub-Saharan Africa|vauthors=Basedau M, Mehler A|year=2005|publisher=GIGA-Hamburg|isbn=978-3-928049-91-7|access-date=November 9, 2020|archive-date=November 9, 2023|archive-url=https://web.archive.org/web/20231109173806/https://books.google.com/books?id=hWrEcl2ydzEC&pg=PA305#v=onepage&q&f=false|url-status=live}}</ref> 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.<ref>{{cite book|title=World Federation of Diamond Bourses (WFDB) and International Diamond Manufacturers Association: Joint Resolution of 19 July 2000|url=https://books.google.com/books?id=fnRnyS7I9cYC&pg=PA334|publisher=World Diamond Council|date=July 19, 2000|access-date=November 5, 2006|isbn=978-90-04-13656-4|archive-date=November 9, 2023|archive-url=https://web.archive.org/web/20231109173808/https://books.google.com/books?id=fnRnyS7I9cYC&pg=PA334#v=onepage&q&f=false|url-status=live}}</ref> 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".<ref name=kimb/>

The Canadian Government has set up a body known as the Canadian Diamond Code of Conduct<ref>{{cite web |title=Voluntary Code of Conduct For Authenticating Canadian Diamond Claims |url=http://www.canadiandiamondcodeofconduct.ca/images/EN_CDCC_Committee_Procedures.pdf |publisher=Canadian Diamond Code Committee|year=2006|access-date=October 30, 2007|archive-date=February 29, 2012|archive-url=https://web.archive.org/web/20120229233018/http://www.canadiandiamondcodeofconduct.ca/images/EN_CDCC_Committee_Procedures.pdf}}</ref> to help authenticate Canadian diamonds. This is a stringent tracking system of diamonds and helps protect the "conflict free" label of Canadian diamonds.<ref>{{cite journal| vauthors = Kjarsgaard BA, Levinson AA |title=Diamonds in Canada|journal=Gems and Gemology|volume=38|issue=3|pages=208–238|year=2002|doi=10.5741/GEMS.38.3.208|doi-access=free|bibcode=2002GemG...38..208K }}</ref>

Mineral resource exploitation in general causes irreversible environmental damage, which must be weighed against the socio-economic benefits to a country.<ref>A meta-analysis of the environmental impact specific to diamond mining is in {{Cite report | vauthors = Oluleye G | title = Environmental Impacts of Mined Diamonds |publisher=Imperial College London Consultants |url=https://www.imperial-consultants.co.uk/wp-content/uploads/2021/02/Final-report-Environmental-Impacts-of-Mined-Diamonds-updated-8-21.pdf |archive-url=https://web.archive.org/web/20211203093203/https://www.imperial-consultants.co.uk/wp-content/uploads/2021/02/Final-report-Environmental-Impacts-of-Mined-Diamonds-updated-8-21.pdf |archive-date=December 3, 2021 |url-status=live |access-date=July 1, 2022}} <!-- NOTE ON DATE: They don't put a date on the case study's page. The page copyright is 2019, but the upload is dated 2021/02, and the report itself cites a 2020 study. Case study url: https://www.imperial-consultants.co.uk/casestudies/meta-study-environmental-impact-of-diamond-mining/ --> <!-- OLD VERSION: https://www.imperial-consultants.co.uk/wp-content/uploads/2021/02/Final-report-Environmental-Impacts-of-Mined-Diamonds.pdf --></ref>

== Synthetics, simulants, and enhancements ==
=== Synthetics ===
{{Main|Synthetic diamond}}

Synthetic diamonds are diamonds manufactured in a laboratory, as opposed to diamonds mined from the Earth. The gemological and industrial uses of diamond have created a large demand for rough stones. This demand has been satisfied in large part by synthetic diamonds, which have been manufactured by various processes for more than half a century. However, in recent years it has become possible to produce gem-quality synthetic diamonds of significant size.<ref name="AMNH"/> 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.<ref name="bain">{{cite web |url=http://www.bain.com/Images/PR_BAIN_REPORT_The_global_diamond_industry.pdf |archive-url=https://web.archive.org/web/20120131062348/http://www.bain.com/Images/PR_BAIN_REPORT_The_global_diamond_industry.pdf |archive-date=January 31, 2012 |url-status=live|title=The Global Diamond Industry: Lifting the Veil of Mystery|publisher=[[Bain and Company|Bain & Company]]|access-date=January 14, 2012}}</ref>

The majority of commercially available synthetic diamonds are yellow and are produced by so-called ''high-pressure high-temperature'' ([[HPHT]]) processes.<ref>{{cite journal| vauthors = Shigley JE, Abbaschian R |title=Gemesis Laboratory Created Diamonds|journal=Gems & Gemology|volume=38|issue=4|pages=301–309|year=2002|doi=10.5741/GEMS.38.4.301|doi-access=free|bibcode=2002GemG...38..301S }}</ref> The yellow color is caused by [[nitrogen]] impurities. Other colors may also be reproduced such as blue, green or pink, which are a result of the addition of [[boron]] or from [[Gemstone irradiation|irradiation]] after synthesis.<ref>{{cite journal| vauthors = Shigley JE, Shen AH, Breeding CM, McClure SF, Shigley JE |title=Lab Grown Colored Diamonds from Chatham Created Gems|journal=Gems & Gemology|volume=40|issue=2|pages=128–145|year=2004|doi=10.5741/GEMS.40.2.128|doi-access=free|bibcode=2004GemG...40..128S }}</ref>

Another popular method of growing synthetic diamond is [[chemical vapor deposition]] (CVD). The growth occurs under low pressure (below atmospheric pressure). It involves feeding a mixture of gases (typically {{nowrap|1 to 99 [[methane]]}} to [[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]].<ref>{{cite journal | vauthors = Werner M, Locher R  |title=Growth and application of undoped and doped diamond films |journal=Reports on Progress in Physics |volume=61 |pages=1665–1710 |year=1998 |doi=10.1088/0034-4885/61/12/002 |issue=12 |bibcode=1998RPPh...61.1665W|s2cid=250878100 }}</ref> This method is mostly used for coatings, but can also produce single crystals several millimeters in size (see picture).<ref name=yarnell/>

As of 2010, nearly all 5,000&nbsp;million carats (1,000{{nbsp}}tonnes) of synthetic diamonds produced per year are for industrial use. Around 50% of the 133&nbsp;million carats of natural diamonds mined per year end up in industrial use.<ref name="bain"/><ref>{{cite web|url=https://www.cnbc.com/2012/08/27/the-billion-dollar-business-of-diamonds-from-mining-to-retail.html|vauthors=Pisani B|title=The Business of Diamonds, From Mining to Retail|publisher=[[CNBC]]|date=August 27, 2012|access-date=September 9, 2017|archive-date=July 7, 2017|archive-url=https://web.archive.org/web/20170707001321/http://www.cnbc.com/id/48782968|url-status=live}}</ref> Mining companies' expenses average 40 to 60&nbsp;US dollars per carat for natural colorless diamonds, while synthetic manufacturers' expenses average {{nowrap|$2,500 per carat}} for synthetic, gem-quality colorless diamonds.<ref name="bain"/>{{rp|79}} However, a purchaser is more likely to encounter a synthetic when looking for a fancy-colored diamond because only 0.01% of natural diamonds are fancy-colored, while most synthetic diamonds are colored in some way.<ref>{{cite book|url=https://books.google.com/books?id=zNicdkuulE4C&pg=PA428|pages=426–430|title=Industrial Minerals & Rocks|vauthors=Kogel JE|publisher=SME|year=2006|isbn=978-0-87335-233-8|access-date=November 9, 2020|archive-date=November 9, 2023|archive-url=https://web.archive.org/web/20231109173917/https://books.google.com/books?id=zNicdkuulE4C&pg=PA428#v=onepage&q&f=false|url-status=live}}</ref>

<gallery widths="200px" heights="180px">
File:HPHTdiamonds2.JPG|alt=Six crystals of cubo-octahedral shapes, each about 2 millimeters in diameter. Two are pale blue, one is pale yellow, one is green-blue, one is dark blue and one green-yellow.|Synthetic diamonds of various colors grown by the high-pressure high-temperature technique
File:Apollo synthetic diamond.jpg|alt=A round, clear gemstone with many facets, the main face being hexagonal, surrounded by many smaller facets.|Colorless gem cut from diamond grown by chemical vapor deposition
</gallery>

=== Simulants ===
{{Main|Diamond simulant}}
[[File:Moissanite ring.JPG|thumb|alt=A round sparkling, clear gemstone with many facets.|Gem-cut synthetic silicon carbide set in a ring]]

A diamond simulant is a non-diamond material that is used to simulate the appearance of a diamond, and may be referred to as diamante. [[Cubic zirconia]] is the most common. The gemstone [[moissanite]] ([[silicon carbide]]) can be treated as a diamond simulant, though more costly to produce than cubic zirconia. Both are produced synthetically.<ref>{{cite book| vauthors = O'Donoghue M, Joyner L |title=Identification of gemstones|pages=12–19|publisher=Butterworth-Heinemann|location=Great Britain|year=2003|isbn=978-0-7506-5512-5}}</ref>

=== Enhancements ===
{{Main|Diamond enhancement}}

Diamond enhancements are specific treatments performed on natural or synthetic diamonds (usually those already cut and polished into a gem), which are designed to better the gemological characteristics of the stone in one or more ways. These include laser drilling to remove inclusions, application of sealants to fill cracks, treatments to improve a white diamond's color grade, and treatments to give fancy color to a white diamond.<ref>{{cite book|url=https://books.google.com/books?id=kCc80Q4gzSgC&pg=PA115|page=115|title=The diamond formula|vauthors=Barnard AS|publisher=Butterworth-Heinemann|year=2000|isbn=978-0-7506-4244-6|access-date=November 9, 2020|archive-date=November 9, 2023|archive-url=https://web.archive.org/web/20231109173812/https://books.google.com/books?id=kCc80Q4gzSgC&pg=PA115#v=onepage&q&f=false|url-status=live}}</ref>

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.<ref>{{cite journal| vauthors = Shigley JE |title=Observations on new coated gemstones|journal=Gemmologie: Zeitschrift der Deutschen Gemmologischen Gesellschaft|volume=56|issue=1–2|pages=53–56|year=2007}}</ref>

=== Identification ===
[[File:Diamond (side view).png|thumb|[[Cathodoluminescence]] image of a diamond, taken in a [[scanning electron microscope]]]]
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 [[thermistor]]s 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.<ref>{{cite patent | inventor = Wenckus JF | country = US | number = 4488821 | title = Method and means of rapidly distinguishing a simulated diamond from natural diamond | pubdate = December 18, 1984 | fdate = November 24, 1982 | pridate = March 3, 1981 | assign1 = Ceres Electronics Corporation }}; {{US patent|4488821}}</ref>

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.<ref name=raman>{{cite book|url=https://books.google.com/books?id=W2cSkEsWbSkC&pg=PA387|pages=387–394|title=Raman spectroscopy in archaeology and art history|vauthors=Edwards HG, Chalmers GM|publisher=Royal Society of Chemistry|year=2005|isbn=978-0-85404-522-8|access-date=November 9, 2020|archive-date=November 9, 2023|archive-url=https://web.archive.org/web/20231109174417/https://books.google.com/books?id=W2cSkEsWbSkC&pg=PA387#v=onepage&q&f=false|url-status=live}}</ref> "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.<ref name=spot/>

Laboratories use techniques such as spectroscopy, microscopy, and luminescence under shortwave ultraviolet light to determine a diamond's origin.<ref name=raman/> 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.<ref>{{cite web |vauthors=Donahue PJ |title=DTC Appoints GIA Distributor of DiamondSure and DiamondView |url=http://www.professionaljeweler.com/archives/news/2004/041904story.html |work=Professional Jeweler Magazine |date=April 19, 2004 |access-date=March 2, 2009 |archive-date=March 6, 2012 |archive-url=https://web.archive.org/web/20120306220856/http://www.professionaljeweler.com/archives/news/2004/041904story.html }}</ref>

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<ref>{{cite web|title=SSEF diamond spotter and SSEF illuminator|url=http://dkamhi.com/ssef%20type%20IIa.htm|publisher=SSEF Swiss Gemmological Institute|access-date=May 5, 2009|archive-url=https://web.archive.org/web/20090627023938/http://dkamhi.com/ssef%20type%20IIa.htm|archive-date=June 27, 2009}}</ref> Diamond Spotter. Stones in the D–Z color range can be examined through the DiamondSure UV/visible spectrometer, a tool developed by De Beers.<ref name=spot>{{cite journal| vauthors = Welbourn C |title=Identification of Synthetic Diamonds: Present Status and Future Developments, Proceedings of the 4th International Gemological Symposium|journal=Gems and Gemology|volume=42|issue=3|pages=34–35|year=2006}}</ref> 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).

== See also ==
{{Portal|Minerals}}
* [[Deep carbon cycle]]
* [[Diamondoid]]
* [[List of diamonds]]
** [[List of largest rough diamonds]]
* [[List of minerals]]
* [[Superhard material]]

== Notes ==
{{notelist}}

== Citations ==
{{Reflist|30em}}

== General and cited references ==
{{refbegin|30em}}
* {{cite book |vauthors=Even-Zohar C |year=2007 |title=From Mine to Mistress: Corporate Strategies and Government Policies in the International Diamond Industry |edition=2nd |publisher=Mining Journal Press |url=http://www.mine2mistress.com/ |access-date=April 18, 2007 |archive-date=March 10, 2020 |archive-url=https://web.archive.org/web/20200310081831/http://www.mine2mistress.com/ |url-status=live }}
* {{cite book | vauthors = Davies G |year=1994 |title=Properties and growth of diamond |publisher=INSPEC |isbn=978-0-85296-875-8}}
* {{cite book | vauthors = O'Donoghue M |title=Gems |publisher=Elsevier |year=2006 |isbn=978-0-7506-5856-0}}
* {{cite book | vauthors = O'Donoghue M, Joyner L |year=2003 |title=Identification of gemstones |publisher=Butterworth-Heinemann |location=Great Britain |isbn=978-0-7506-5512-5}}
* {{cite book | vauthors = Feldman A, Robins LH |year=1991 |title=Applications of Diamond Films and Related Materials |publisher=Elsevier|isbn=978-1-48329124-6}}
* {{cite book | vauthors = Field JE |year=1979 |title=The Properties of Diamond |publisher=Academic Press |location=London |isbn=978-0-12-255350-9}}
* {{cite book | vauthors = Field JE |year=1992 |title=The Properties of Natural and Synthetic Diamond |publisher=Academic Press |location=London |isbn=978-0-12-255352-3}}
* {{cite book |vauthors=Hershey W |year=2004|edition=Reprint|orig-date=1940 |title=The Book of Diamonds |publisher=Hearthside Press New York |url=http://www.farlang.com/diamonds/hershey-diamond-chapters/page_001 |isbn=978-1-4179-7715-4 |access-date=August 18, 2011 |archive-date=August 20, 2014 |archive-url=https://web.archive.org/web/20140820053011/http://www.farlang.com/diamonds/hershey-diamond-chapters/page_001 |url-status=live }}
* {{cite book |vauthors=Koizumi S, Nebel CE, Nesladek M |year=2008 |title=Physics and Applications of CVD Diamond |publisher=Wiley VCH |isbn=978-3-527-40801-6 |url=https://books.google.com/books?id=pRFUZdHb688C |access-date=November 9, 2020 |archive-date=November 9, 2023 |archive-url=https://web.archive.org/web/20231109174432/https://books.google.com/books?id=pRFUZdHb688C |url-status=live }}
* {{cite book |vauthors=Pan LS, Kani DR |year=1995 |title=Diamond: Electronic Properties and Applications |publisher=Kluwer Academic Publishers |url=https://books.google.com/books?id=ZtfFEoXkU8wC&pg=PP1 |isbn=978-0-7923-9524-9 }}
* {{cite book | vauthors = Pagel-Theisen V |year=2001 |title=Diamond Grading ABC: the Manual |publisher=Rubin & Son |location=Antwerp |isbn=978-3-9800434-6-5}}
* {{cite book | vauthors = Radovic RL, Walker RM, Thrower PA | author-link3 = Peter Thrower |year=1965 |title=Chemistry and physics of carbon: a series of advances |publisher=Marcel Dekker |location=New York |isbn=978-0-8247-0987-7}}
* {{cite book |vauthors=Tolkowsky M |year=1919 |title=Diamond Design: A Study of the Reflection and Refraction of Light in a Diamond |publisher=E. & F.N. Spon |location=London |url=http://www.folds.net/diamond/index.html |access-date=March 13, 2007 |archive-date=March 12, 2023 |archive-url=https://web.archive.org/web/20230312204834/http://www.folds.net/diamond/index.html |url-status=live }}
* {{cite book |vauthors=Wise RW |year=2016 |title=Secrets of the Gem Trade: The Connoisseur's Guide to Precious Gemstones |isbn=978-0-9728223-2-9 |publisher=Brunswick House Press |url=http://secretsofthegemtrade.com/ |edition=Second |access-date=May 11, 2021 |archive-date=August 19, 2019 |archive-url=https://web.archive.org/web/20190819182845/http://secretsofthegemtrade.com/ |url-status=live }}
* {{cite book |vauthors=Zaitsev AM |year=2001 |title=Optical Properties of Diamond: A Data Handbook |publisher=Springer |url=https://books.google.com/books?id=msU4jkdCEhIC&pg=PP1 |isbn=978-3-540-66582-3 |access-date=November 9, 2020 |archive-date=November 9, 2023 |archive-url=https://web.archive.org/web/20231109174953/https://books.google.com/books?id=msU4jkdCEhIC&pg=PP1#v=onepage&q&f=false |url-status=live }}
{{refend}}

== Further reading ==
* {{Cite magazine | vauthors = Epstein EJ |date=February 1982 |title=Have You Ever Tried to Sell a Diamond? |url=https://www.theatlantic.com/doc/198202/diamond |archive-url=https://web.archive.org/web/20060315041428/https://www.theatlantic.com/doc/198202/diamond |archive-date=March 15, 2006 |magazine=[[The Atlantic (magazine)|The Atlantic Monthly]] |access-date=January 2, 2023}}
* {{Cite web | vauthors = Tyson P |date=November 2000 |title=Diamonds in the Sky |url=https://www.pbs.org/wgbh/nova/diamond/sky.html |department=The Diamond Deception |work=[[Nova (American TV program)|Nova]] |publisher=[[PBS]] |access-date=January 2, 2023}}

== External links ==
{{wikibooks|Development Cooperation Handbook|Stories/Unsustainable Growth|Unsustainable Growth}}
{{Sister project links |wikt=diamond |commons=Diamond |b=no |n=no |q=Diamond |s=no |v=no}}
* [http://www.ioffe.ru/SVA/NSM/Semicond/Diamond/index.html Properties of diamond: Ioffe database]
* {{cite web|url=https://www.gia.edu/doc/A-Contribution-to-Understanding-the-Effect-of-Blue-Fluorescence-on-the-Appearance-of-Diamonds |archive-url=https://web.archive.org/web/20170908111042/https://www.gia.edu/doc/A-Contribution-to-Understanding-the-Effect-of-Blue-Fluorescence-on-the-Appearance-of-Diamonds | title="A Contribution to the Understanding of Blue Fluorescence on the Appearance of Diamonds" |date=2007 |work=Gemological Institute of America (GIA) |archive-date=September 8, 2017 }}

{{Allotropes of carbon}}
{{Jewellery}}
{{Gemstones}}
{{Mohs}}
{{Authority control}}

[[Category:Diamond| ]]
[[Category:Abrasives]]
[[Category:Articles containing video clips]]
[[Category:Crystals]]
[[Category:Cubic minerals]]
[[Category:Economic geology]]
[[Category:Group IV semiconductors]]
[[Category:Impact event minerals]]
[[Category:Industrial minerals]]
[[Category:Luminescent minerals]]
[[Category:Minerals in space group 227]]
[[Category:Native element minerals]]
[[Category:Transparent materials]]