Editing Carbon

{{About|the chemical element}}
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{{Infobox carbon}}

'''Carbon''' ({{etymology|la|{{wikt-lang|la|carbo}}|coal}}) is a [[chemical element]];  it has [[chemical symbol|symbol]] '''C''' and [[atomic number]] 6. It is [[nonmetal]]lic and [[tetravalence|tetravalent]]—meaning that its [[atom]]s are able to form up to four [[covalent bond]]s due to its [[valence shell]] exhibiting 4 electrons. It belongs to group 14 of the [[periodic table]].<ref>{{cite web |title=carbon {{!}} Facts, Uses, & Properties |url=https://www.britannica.com/science/carbon-chemical-element|website=Encyclopedia Britannica|language=en|url-status=live |archive-url=https://web.archive.org/web/20171024183827/https://www.britannica.com/science/carbon-chemical-element|archive-date=2017-10-24}}</ref> Carbon makes up about 0.025 percent of Earth's crust.<ref>{{cite web |url=https://www.britannica.com/science/carbon-chemical-element |title=carbon |website=Britannica encyclopedia|date=22 February 2024 }}</ref> Three [[Isotopes of carbon|isotopes]] occur naturally, [[carbon-12|{{sup|12}}C]] and [[carbon-13|{{sup|13}}C]] being stable, while [[carbon-14|{{sup|14}}C]] is a [[radionuclide]], decaying with a [[half-life]] of 5,700&nbsp;years.{{NUBASE 2020|ref}} Carbon is one of the [[timeline of chemical element discoveries#Pre-modern and early modern discoveries|few elements known since antiquity]].<ref name="History of Carbon">{{cite web |url=http://www.caer.uky.edu/carbon/history/carbonhistory.shtml |title=History of Carbon |access-date=2013-01-10 |url-status=dead |archive-url=https://web.archive.org/web/20121101085829/http://www.caer.uky.edu/carbon/history/carbonhistory.shtml |archive-date=2012-11-01}}</ref>

Carbon is the 15th [[abundance of elements in Earth's crust|most abundant element in the Earth's crust]], and the [[abundance of the chemical elements|fourth most abundant element in the universe by mass]] after [[hydrogen]], [[helium]], and [[oxygen]]. Carbon's abundance, its unique diversity of [[organic compound]]s, and its unusual ability to form [[polymer]]s at the temperatures commonly encountered on Earth, enables this element to serve as a common element of [[carbon-based life|all known life]]. It is the second most abundant element in the human body by mass (about 18.5%) after oxygen.<ref>{{cite book |title=Campbell Biology |last=Reece |first=Jane B. |date=31 October 2013 |publisher=[[Pearson Education|Pearson]] |isbn=978-0-321-77565-8 |edition=10}}</ref>

The atoms of carbon can bond together in diverse ways, resulting in various [[allotropes of carbon]]. Well-known [[allotropes]] include [[graphite]], [[diamond]], [[amorphous carbon]], and [[fullerenes]]. The [[physical properties]] of carbon vary widely with the allotropic form. For example, graphite is [[opaque]] and black, while diamond is highly [[transparency (optics)|transparent]]. Graphite is soft enough to form a streak on paper (hence its name, from the Greek verb "γράφειν" which means "to write"), while diamond is the hardest naturally occurring material known. Graphite is a good [[electrical conductor]] while diamond has a low [[electrical conductivity]]. Under normal conditions, diamond, [[carbon nanotube]]s, and [[graphene]] have the highest [[thermal conductivities]] of all known materials. All carbon allotropes are solids under normal conditions, with graphite being the most [[thermodynamic equilibrium|thermodynamically stable]] form at standard temperature and pressure. They are chemically resistant and require high temperature to react even with oxygen.

The most common [[oxidation state]] of carbon in [[inorganic compound]]s is +4, while +2 is found in [[carbon monoxide]] and [[transition metal]] [[metal carbonyl|carbonyl]] complexes. The largest sources of inorganic carbon are [[limestone]]s, [[dolomite (mineral)|dolomites]] and [[carbon dioxide]], but significant quantities occur in organic deposits of [[coal]], [[peat]], [[petroleum|oil]], and [[methane clathrate]]s. Carbon forms a vast number of [[chemical compound|compounds]], with about two hundred million having been described and indexed;<ref name="ChemAbs-2023">{{cite web |author=Chemical Abstracts Service |author-link=Chemical Abstracts Service |date=2023 |url=https://www.cas.org/cas-data/cas-registry |title=CAS Registry |access-date=2023-02-12}}</ref> and yet that number is but a fraction of the number of theoretically possible compounds under standard conditions.

==Characteristics==
[[File:Carbon-phase-diagramp.svg|thumb|left|upright=1.3|Theoretically predicted phase diagram of carbon, from 1989. Newer work indicates that the melting point of diamond (top-right curve) does not go above about 9000&nbsp;K.<ref name="Eggert-2009">{{cite journal |display-authors=etal |last1=J.H. Eggert |title=Melting temperature of diamond at ultrahigh pressure |journal=Nature Physics |date=Nov 8, 2009 |volume=6 |issue=1 |pages=40–43 |doi=10.1038/nphys1438 |doi-access=free|bibcode=2010NatPh...6...40E }}</ref>]]
The [[allotropes of carbon]] include [[graphite]], one of the softest known substances, and [[diamond]], the hardest naturally occurring substance. It [[Chemical bond|bonds]] readily with other small atoms, including other carbon atoms, and is capable of forming multiple stable [[covalent]] bonds with suitable multivalent atoms. Carbon is a component element in the large majority of all [[chemical compound]]s, with about two hundred million examples having been described in the published chemical literature.<ref name="ChemAbs-2023"/> Carbon also has the highest [[sublimation (phase transition)|sublimation]] point of all elements. At [[atmospheric pressure]] it has no melting point, as its [[triple point]] is at {{convert|10.8|±|0.2|MPa|atm psi}} and {{convert|4600|±|300|K|C F|-1}},<ref name="triple2" /><ref name="triple3" /> so it sublimes at about {{convert|3900|K|C F}}.<ref name="Greenville Whittaker-1978">{{cite journal |journal=Nature |volume=276 |pages=695–696 |date=1978 |doi=10.1038/276695a0 |title=The controversial carbon solid−liquid−vapour triple point |first=A. |last=Greenville Whittaker |issue=5689 |bibcode=1978Natur.276..695W |s2cid=4362313}}</ref><ref>{{cite news |url=http://lbruno.home.cern.ch/lbruno/documents/Bibliography/LHC_Note_78.pdf |title=On Graphite Transformations at High Temperature and Pressure Induced by Absorption of the LHC Beam |first=J. M. |last=Zazula |date=1997 |access-date=2009-06-06 |publisher=CERN |url-status=live |archive-url=https://web.archive.org/web/20090325230751/http://lbruno.home.cern.ch/lbruno/documents/Bibliography/LHC_Note_78.pdf |archive-date=2009-03-25}}</ref> Graphite is much more reactive than diamond at standard conditions, despite being more thermodynamically stable, as its delocalised [[pi bond|pi system]] is much more vulnerable to attack. For example, graphite can be oxidised by hot concentrated [[nitric acid]] at standard conditions to [[mellitic acid]], C<sub>6</sub>(CO<sub>2</sub>H)<sub>6</sub>, which preserves the hexagonal units of graphite while breaking up the larger structure.{{sfn|Greenwood|Earnshaw|1997|pages=289-292}}

Carbon is the sixth element, with a ground-state [[electron configuration]] of 1s<sup>2</sup>2s<sup>2</sup>2p<sup>2</sup>, of which the four outer electrons are [[valence electron]]s. Its first four ionisation energies, 1086.5, 2352.6, 4620.5 and 6222.7&nbsp;kJ/mol, are much higher than those of the heavier group-14 elements. The electronegativity of carbon is 2.5, significantly higher than the heavier group-14 elements (1.8–1.9), but close to most of the nearby nonmetals, as well as some of the second- and third-row [[transition metal]]s. Carbon's [[covalent radii]] are normally taken as 77.2&nbsp;pm (C−C), 66.7&nbsp;pm (C=C) and 60.3&nbsp;pm (C≡C), although these may vary depending on coordination number and what the carbon is bonded to. In general, covalent radius decreases with lower coordination number and higher bond order.{{sfn|Greenwood|Earnshaw|1997|pages=276-278}}

Carbon-based compounds form the basis of all known life on Earth, and the [[carbon-nitrogen-oxygen cycle]] provides a small portion of the energy produced by the Sun, and most of the energy in larger stars (e.g. [[Sirius]]). Although it forms an extraordinary variety of compounds, most forms of carbon are comparatively unreactive under normal conditions. At standard temperature and pressure, it resists all but the strongest oxidizers. It does not react with [[sulfuric acid]], [[hydrochloric acid]], [[chlorine]] or any [[Alkali metals|alkalis]]. At elevated temperatures, carbon reacts with oxygen to form [[carbon oxides]] and will rob oxygen from metal oxides to leave the elemental metal. This [[exothermic reaction]] is used in the iron and steel industry to [[smelting|smelt]] iron and to control the carbon content of [[steel]]:{{sfn|Greenwood|Earnshaw|1997|pages=289-301}}
:{{chem|Fe|3|O|4}} + 4 C{{sub|(s)}} + 2 {{chem|O|2}} → 3 Fe{{sub|(s)}} + 4 {{chem|CO|2}}{{sub|(g)}}.

Carbon reacts with sulfur to form [[carbon disulfide]], and it reacts with steam in the coal-gas reaction used in [[coal gasification]]:{{sfn|Greenwood|Earnshaw|1997|pages=290}}<ref>{{cite journal | last=Warnecke | first=Friedrich | title=Die gewerbliche Schwefelkohlenstoffvergiftung | journal=Archiv für Gewerbepathologie und Gewerbehygiene | publisher=Springer Science and Business Media LLC | volume=11 | issue=2 | year=1941 | issn=0340-0131 | doi=10.1007/bf02122927 | pages=198–248 | bibcode=1941IAOEH..11..198W | s2cid=72106188 | language=de}}</ref><ref>{{cite book|title=The chemistry of gas lighting|first=Lewis|last=Thompson|pages=91–98|publisher=Office of "The Journal of Gas Lighting"|date=1850|url=https://books.google.com/books?id=sac_AAAAYAAJ}}</ref>

:C{{sub|(s)}} + H{{sub|2}}O{{sub|(g)}} → CO{{sub|(g)}} + H{{sub|2(g)}}.

Carbon combines with some metals at high temperatures to form metallic carbides, such as the iron carbide [[cementite]] in steel and [[tungsten carbide]], widely used as an abrasive and for making hard tips for cutting tools.{{sfn|Greenwood|Earnshaw|1997|pages=297-300}}<ref name="carbideu">{{cite book |author1=Helmut Tulhoff |author2=Juliane A. Meese-Marktscheffel |author3=Carina Oelgardt |author4=Christian Kind |author5=Markus Weinmann |author6=Tino Säuberlich |title=Ullmann's Encyclopedia of Industrial Chemistry |date=2017 |isbn=9783527306732 |pages=5–11 |language=en |chapter=Carbides |doi=10.1002/14356007.a05_061.pub2}}</ref>

The system of carbon allotropes spans a range of extremes:
{|class="wikitable"
|Graphite is one of the softest materials known.
|style="width: 50%;"|Synthetic [[aggregated diamond nanorod|nanocrystalline diamond]] is the hardest material known.<ref>{{cite journal |last1=Irifune |first1=Tetsuo |last2=Kurio |first2=Ayako |last3=Sakamoto |first3=Shizue |last4=Inoue |first4=Toru |last5=Sumiya |first5=Hitoshi |title=Materials: Ultrahard polycrystalline diamond from graphite |journal=Nature |volume=421 |pages=599–600 |date=2003 |doi=10.1038/421599b |pmid=12571587 |issue=6923 |bibcode=2003Natur.421..599I |s2cid=52856300}}</ref>
|-
|Graphite is a very good lubricant, displaying [[superlubricity]].<ref>{{cite journal |title=Superlubricity of Graphite |url=http://www.physics.leidenuniv.nl/sections/cm/ip/group/PDF/Phys.rev.lett/2004/92(2004)12601.pdf |date=2004 |last1=Dienwiebel |first1=Martin |last2=Verhoeven |first2=Gertjan |last3=Pradeep |first3=Namboodiri |last4=Frenken |first4=Joost |last5=Heimberg |first5=Jennifer |last6=Zandbergen |first6=Henny |journal=Physical Review Letters |volume=92 |issue=12 |pages=126101 |bibcode=2004PhRvL..92l6101D |doi=10.1103/PhysRevLett.92.126101 |pmid=15089689 |s2cid=26811802 |url-status=live |archive-url=https://web.archive.org/web/20110917120623/http://www.physics.leidenuniv.nl/sections/cm/ip/group/PDF/Phys.rev.lett/2004/92(2004)12601.pdf |archive-date=2011-09-17}}</ref>
|Diamond is the ultimate abrasive.
|-
|Graphite is a [[electrical conductor|conductor]] of electricity.<ref>{{cite journal |last1=Deprez |first1=N. |last2=McLachan |first2=D. S. |date=1988 |title=The analysis of the electrical conductivity of graphite conductivity of graphite powders during compaction |journal=[[Journal of Physics D: Applied Physics]] |volume=21 |issue=1 |pages=101–107 |doi=10.1088/0022-3727/21/1/015 |bibcode=1988JPhD...21..101D |s2cid=250886376}}</ref>
|Diamond is an excellent electrical [[insulator (electrical)|insulator]],<ref>{{cite journal |last=Collins |first=A. T. |title=The Optical and Electronic Properties of Semiconducting Diamond |journal=[[Philosophical Transactions of the Royal Society A]] |volume=342 |pages=233–244 |date=1993 |doi=10.1098/rsta.1993.0017 |issue=1664 |bibcode=1993RSPTA.342..233C |s2cid=202574625}}</ref> and has the highest breakdown electric field of any known material.
|-
|Some forms of graphite are used for [[thermal insulation]] (i.e. firebreaks and heat shields), but some [[pyrolytic graphite|other forms]] are good thermal conductors.
|Diamond is the best known naturally occurring [[list of thermal conductivities|thermal conductor]].
|-
|Graphite is [[opaque]].
|Diamond is highly transparent.
|-
|Graphite crystallizes in the [[hexagonal system]].<ref>{{cite book |title=Graphite and Precursors |author=Delhaes, P. |publisher=CRC Press |date=2001 |url=https://books.google.com/books?id=7p2pgNOWPbEC&pg=PA146 |isbn=978-90-5699-228-6}}</ref>
|Diamond crystallizes in the [[cubic system]].
|-
|Amorphous carbon is completely [[isotropic]].
|Carbon nanotubes are among the most [[anisotropic]] materials known.
|}

===Allotropes===
{{Main|Allotropes of carbon}}
[[Atomic carbon]] is a very short-lived species and, therefore, carbon is stabilized in various multi-atomic structures with diverse molecular configurations called [[allotrope]]s. The three relatively well-known allotropes of carbon are [[amorphous carbon]], [[graphite]], and diamond. Once considered exotic, [[fullerene]]s are nowadays commonly synthesized and used in research; they include [[buckyball]]s,<ref name="Unwin-2007"/><ref name="Ebbesen-1997">{{cite book |editor=Ebbesen, T. W. |editor-link=Thomas Ebbesen |date=1997 |title=Carbon nanotubes—preparation and properties |publisher=CRC Press |location=Boca Raton, Florida |isbn=978-0-8493-9602-1}}</ref> [[carbon nanotube]]s,<ref name="Springer-2001">{{cite book |editor=Dresselhaus, M. S. |editor-link1=Mildred Dresselhaus |editor2=Dresselhaus, G. |editor3=Avouris, Ph. |editor-link3=Phaedon Avouris |date=2001 |title=Carbon nanotubes: synthesis, structures, properties and applications |series=Topics in Applied Physics |volume=80 |isbn=978-3-540-41086-7 |location=Berlin |publisher=Springer}}</ref> [[carbon nanobud]]s<ref name="Nasibulin-2007">{{cite journal |date=2007 |title=A novel hybrid carbon material |journal=Nature Nanotechnology |volume=2 |issue=3 |pages=156–161 |doi=10.1038/nnano.2007.37 |pmid=18654245 |s2cid=6447122 |bibcode=2007NatNa...2..156N |doi-access=free |last1=Nasibulin |first1=Albert G. |author-link1=Albert Nasibulin |last2=Pikhitsa |first2=P. V. |last3=Jiang |first3=H. |last4=Brown |first4=D. P. |last5=Krasheninnikov |first5=A. V. |last6=Anisimov |first6=A. S. |last7=Queipo |first7=P. |last8=Moisala |first8=A. |last9=Gonzalez |first9=D. |display-authors=8}}</ref> and [[carbon nanofibers|nanofibers]].<ref>{{cite journal |date=2007 |title=Investigations of NanoBud formation |journal=Chemical Physics Letters |volume=446 |issue=1 |pages=109–114 |doi=10.1016/j.cplett.2007.08.050 |bibcode=2007CPL...446..109N |last1=Nasibulin |first1=A. |last2=Anisimov |first2=Anton S. |last3=Pikhitsa |first3=Peter V. |last4=Jiang |first4=Hua |last5=Brown |first5=David P. |last6=Choi |first6=Mansoo |last7=Kauppinen |first7=Esko I.}}</ref><ref>{{cite journal |date=2004 |title=Synthesis and characterisation of carbon nanofibers with macroscopic shaping formed by catalytic decomposition of C{{sub |2}}H{{sub|6}}/H{{sub|2}} over nickel catalyst |journal=Applied Catalysis A: General|volume=274|issue=1–2|pages=1–8|doi=10.1016/j.apcata.2004.04.008 |author=Vieira, R |last2=Ledoux|first2=Marc-Jacques |last3=Pham-Huu|first3=Cuong}}</ref> Several other exotic allotropes have also been discovered, such as [[lonsdaleite]],<ref name="Frondel-1967">{{cite journal |date=1967 |title=Lonsdaleite, a new hexagonal polymorph of diamond |journal=Nature |volume=214 |pages=587–589 |issue=5088 |bibcode=1967Natur.214..587F |s2cid=4184812 |doi=10.1038/214587a0 |first1=Clifford |last1=Frondel |last2=Marvin |first2=Ursula B. |author-link2=Ursula Marvin}}</ref> [[glassy carbon]],<ref name="Harris-2004"/> [[carbon nanofoam]]<ref>{{cite journal |date=1999 |title=Structural analysis of a carbon foam formed by high pulse-rate laser ablation |journal=Applied Physics A: Materials Science & Processing |volume=69 |pages=S755–S758 |doi=10.1007/s003390051522 |issue=7 |bibcode=1999ApPhA..69S.755R |s2cid=96050247 |author=Rode, A. V. |last2=Hyde |first2=S. T. |last3=Gamaly |first3=E. G. |last4=Elliman |first4=R. G. |last5=McKenzie |first5=D. R. |last6=Bulcock |first6=S.}}</ref> and [[linear acetylenic carbon]] (carbyne).<ref name="Heimann-1999">{{cite book |author=Heimann, Robert Bertram |author2=Evsyukov, Sergey E. |author3=Kavan, Ladislav |name-list-style=amp |title=Carbyne and carbynoid structures |url=https://books.google.com/books?id=swSQZcTmo_4C&pg=PA1 |access-date=2011-06-06 |date=28 February 1999 |publisher=Springer |isbn=978-0-7923-5323-2 |pages=1– |url-status=live |archive-url=https://web.archive.org/web/20121123153424/http://books.google.com/books?id=swSQZcTmo_4C&pg=PA1 |archive-date=23 November 2012}}</ref>

[[Graphene]] is a two-dimensional sheet of carbon with the atoms arranged in a hexagonal lattice. As of 2009, graphene appears to be the strongest material ever tested.<ref name="Lee-2008">{{cite journal |last1=Lee |first1=C. |last2=Wei |first2=X. |last3=Kysar |first3=J. W. |last4=Hone |first4=J. |date=2008 |title=Measurement of the Elastic Properties and Intrinsic Strength of Monolayer Graphene |journal=Science |volume=321 |issue=5887 |pages=385–8 |bibcode=2008Sci...321..385L |doi=10.1126/science.1157996 |pmid=18635798 |s2cid=206512830}}
* {{cite press release |author=Phil Schewe |date=July 28, 2008 |title=World's Strongest Material |website=Inside Science News Service |url=http://www.aip.org/isns/reports/2008/027.html |archive-url=https://web.archive.org/web/20090531134104/http://www.aip.org/isns/reports/2008/027.html |archive-date=2009-05-31}}</ref> The process of separating it from graphite will require some further technological development before it is economical for industrial processes.<ref name="Sanderson-2008">{{cite web |url=http://www.nypost.com/seven/08252008/news/regionalnews/toughest_stuff__known_to_man_125993.htm |title=Toughest Stuff Known to Man : Discovery Opens Door to Space Elevator |last=Sanderson |first=Bill |date=2008-08-25 |publisher=nypost.com |access-date=2008-10-09 |url-status=live |archive-url=https://web.archive.org/web/20080906171324/http://www.nypost.com/seven/08252008/news/regionalnews/toughest_stuff__known_to_man_125993.htm |archive-date=2008-09-06}}</ref> If successful, graphene could be used in the construction of a [[space elevator]]. It could also be used to safely store hydrogen for use in a hydrogen based engine in cars.<ref>{{cite journal |last1=Jin |first1=Zhong |last2=Lu |first2=Wei |last3=O'Neill |first3=Kevin J. |last4=Parilla |first4=Philip A. |last5=Simpson |first5=Lin J. |last6=Kittrell |first6=Carter |last7=Tour |first7=James M. |date=2011-02-22 |title=Nano-Engineered Spacing in Graphene Sheets for Hydrogen Storage |journal=Chemistry of Materials |volume=23 |issue=4 |pages=923–925 |doi=10.1021/cm1025188 |issn=0897-4756}}</ref>

[[File:Glassy carbon and a 1cm3 graphite cube HP68-79.jpg|thumb|left|A large sample of glassy carbon]] The [[amorphous]] form is an assortment of carbon atoms in a non-crystalline, irregular, glassy state, not held in a crystalline macrostructure. It is present as a powder, and is the main constituent of substances such as charcoal, [[lampblack]] (soot), and [[activated carbon]]. At normal pressures, carbon takes the form of graphite, in which each atom is bonded trigonally to three others in a plane composed of fused [[hexagon]]al rings, just like those in [[aromatic hydrocarbon]]s.<ref>{{cite book |title=The polymorphism of elements and compounds |last=Jenkins |first=Edgar |date=1973 |publisher=Taylor & Francis |isbn=978-0-423-87500-3 |page=30 |url=https://books.google.com/books?id=XNYOAAAAQAAJ&pg=PA30 |access-date=2011-05-01 |url-status=live |archive-url=https://web.archive.org/web/20121123204229/http://books.google.com/books?id=XNYOAAAAQAAJ&pg=PA30 |archive-date=2012-11-23}}</ref> The resulting network is 2-dimensional, and the resulting flat sheets are stacked and loosely bonded through weak [[van der Waals force]]s.<!-- no evidence for upper case van der Waals; see [[Talk:Van der Waals#Van should be capitalized unless preceded by first name]] rebuttal --> This gives graphite its softness and its [[cleavage (crystal)|cleaving]] properties (the sheets slip easily past one another). Because of the delocalization of one of the outer electrons of each atom to form a [[delocalized electron|π-cloud]], graphite conducts [[electricity]], but only in the plane of each [[covalently bonded]] sheet. This results in a lower bulk [[electrical conductivity]] for carbon than for most metals. The delocalization also accounts for the energetic stability of graphite over diamond at room temperature.{{sfn|Greenwood|Earnshaw|1997|pages=274-278}}

[[File:Eight Allotropes of Carbon.svg|thumb|upright=1.35|Some allotropes of carbon: a) [[diamond]]; b) [[graphite]]; c) [[lonsdaleite]]; d–f) [[fullerene]]s (C{{sub|60}}, C{{sub|540}}, C{{sub|70}}); g) [[amorphous carbon]]; h) [[carbon nanotube]]]]

At very high pressures, carbon forms the more compact allotrope, diamond, having nearly twice the density of graphite. Here, each atom is bonded [[tetrahedron|tetrahedrally]] to four others, forming a 3-dimensional network of puckered six-membered rings of atoms. Diamond has the same [[cubic structure]] as [[silicon]] and [[germanium]], and because of the strength of the carbon-carbon [[chemical bond|bonds]], it is the hardest naturally occurring substance measured by [[Mohs scale|resistance to scratching]]. Contrary to the popular belief that ''"diamonds are forever"'', they are thermodynamically unstable ([[Standard Gibbs free energy of formation|Δ<sub>f</sub>''G''°]](diamond, 298&nbsp;K) = 2.9&nbsp;kJ/mol<ref>{{cite journal |last1=Rossini |first1=F. D. |last2=Jessup |first2=R. S. |date=1938 |title=Heat and Free Energy of Formation of Carbon Dioxide and of the Transition Between Graphite and Diamond |journal=Journal of Research of the National Bureau of Standards |volume=21 |issue=4 |pages=491 |doi=10.6028/jres.021.028 |doi-access=free}}</ref>) under normal conditions (298&nbsp;K, 10<sup>5</sup>&nbsp;Pa) and should theoretically transform into graphite.<ref name="World of Carbon">{{cite web |url=http://invsee.asu.edu/nmodules/Carbonmod/point.html |archive-url=https://web.archive.org/web/20010531203728/http://invsee.asu.edu/nmodules/Carbonmod/point.html |url-status=dead |archive-date=2001-05-31 |title=World of Carbon&nbsp;– Interactive Nano-visulisation in Science & Engineering Education (IN-VSEE) |access-date=2008-10-09}}</ref> But due to a high [[activation energy]] barrier, the transition into graphite is so slow at normal temperature that it is unnoticeable. However, at very high temperatures diamond will turn into graphite, and diamonds can burn up in a house fire. The bottom left corner of the phase diagram for carbon has not been scrutinized experimentally. Although a computational study employing [[density functional theory]] methods reached the conclusion that as {{nowrap|''T'' → 0 K}} and {{nowrap|''p'' → 0 Pa}}, diamond becomes more stable than graphite by approximately 1.1&nbsp;kJ/mol,<ref>{{cite journal |last=Grochala |first=Wojciech |date=2014-04-01 |title=Diamond: Electronic Ground State of Carbon at Temperatures Approaching 0 K |journal=Angewandte Chemie International Edition |language=en |volume=53 |issue=14 |pages=3680–3683 |doi=10.1002/anie.201400131 |pmid=24615828 |issn=1521-3773 |s2cid=13359849}}</ref> more recent and definitive experimental and computational studies show that graphite is more stable than diamond for {{nowrap|''T'' < 400 K}}, without applied pressure, by 2.7&nbsp;kJ/mol at ''T''&nbsp;=&nbsp;0&nbsp;K and 3.2&nbsp;kJ/mol at ''T''&nbsp;=&nbsp;298.15&nbsp;K.<ref>{{cite journal |first1=Mary Anne |last1=White |author-link1=Mary Anne White |first2=Samer |last2=Kahwaji |first3=Vera L. S. |last3=Freitas |first4=Riko |last4=Siewert |first5=Joseph A. |last5=Weatherby |first6=Maria D. M. C. |last6=Ribeiro da Silva |first7=Sergey P. |last7=Verevkin |first8=Erin R. |last8=Johnson |first9=Josef W. |last9=Zwanziger |date=2021 |title=The Relative Thermal Stability of Diamond and Graphite |journal=Angewandte Chemie International Edition |language=en |volume=60 |issue=3 |pages=1546–1549 |doi=10.1002/anie.202009897 |issn=1433-7851 |pmid=32970365 |s2cid=221888151}}</ref> Under some conditions, carbon crystallizes as [[lonsdaleite]], a [[hexagonal crystal family|hexagonal crystal lattice]] with all atoms covalently bonded and properties similar to those of diamond.<ref name="Frondel-1967"/>

[[Fullerene]]s are a synthetic crystalline formation with a graphite-like structure, but in place of flat [[hexagonal crystal system|hexagonal cells]] only, some of the cells of which fullerenes are formed may be pentagons, nonplanar hexagons, or even heptagons of carbon atoms. The sheets are thus warped into spheres, ellipses, or cylinders. The properties of fullerenes (split into buckyballs, buckytubes, and nanobuds) have not yet been fully analyzed and represent an intense area of research in [[nanomaterial]]s. The names ''fullerene'' and ''buckyball'' are given after [[Richard Buckminster Fuller]], popularizer of [[geodesic dome]]s, which resemble the structure of fullerenes. The buckyballs are fairly large molecules formed completely of carbon bonded trigonally, forming [[spheroid]]s (the best-known and simplest is the soccerball-shaped C{{sub|60}} [[buckminsterfullerene]]).<ref name="Unwin-2007"/> Carbon nanotubes (buckytubes) are structurally similar to buckyballs, except that each atom is bonded trigonally in a curved sheet that forms a hollow [[cylinder]].<ref name="Ebbesen-1997"/><ref name="Springer-2001"/> Nanobuds were first reported in 2007 and are hybrid buckytube/buckyball materials (buckyballs are covalently bonded to the outer wall of a nanotube) that combine the properties of both in a single structure.<ref name="Nasibulin-2007"/>

[[File:C2014_Q2.jpg|thumb|Comet [[C/2014 Q2 (Lovejoy)]] surrounded by glowing carbon vapor]]
Of the other discovered allotropes, carbon nanofoam is a ferromagnetic allotrope discovered in 1997. It consists of a low-density cluster-assembly of carbon atoms strung together in a loose three-dimensional web, in which the atoms are bonded trigonally in six- and seven-membered rings. It is among the lightest known solids, with a density of about 2&nbsp;kg/m{{sup|3}}.<ref>{{cite journal |url=http://www.aip.org/pnu/2004/split/678-1.html |title=Carbon Nanofoam is the World's First Pure Carbon Magnet |journal=Physics News Update |url-status=live |volume=678 |issue=1 |date=March 26, 2004 |author=Schewe, Phil |author2=Stein, Ben |name-list-style=amp |archive-url=https://web.archive.org/web/20120307104655/http://www.aip.org/pnu/2004/split/678-1.html |archive-date=March 7, 2012}}</ref> Similarly, [[glassy carbon]] contains a high proportion of closed [[porosity]],<ref name="Harris-2004"/> but contrary to normal graphite, the graphitic layers are not stacked like pages in a book, but have a more random arrangement. [[Linear acetylenic carbon]]<ref name="Heimann-1999"/> has the chemical structure<ref name="Heimann-1999"/> −(C≡C){{sub|{{mvar|n}}}}−&nbsp;. Carbon in this modification is linear with ''sp'' [[orbital hybridization]], and is a [[polymer]] with alternating single and triple bonds. This carbyne is of considerable interest to [[nanotechnology]] as its [[Young's modulus]] is 40&nbsp;times that of the hardest known material&nbsp;– diamond.<ref>{{cite journal |last1=Itzhaki |first1=Lior |last2=Altus |first2=Eli |last3=Basch |first3=Harold |last4=Hoz |first4=Shmaryahu |year=2005 |title=Harder than diamond: Determining the cross-sectional area and Young's modulus of molecular rods |journal=Angew. Chem. Int. Ed. |volume=44 |issue=45 |pages=7432–7435 |pmid=16240306 |doi=10.1002/anie.200502448}}</ref>

In 2015, a team at the [[North Carolina State University]] announced the development of another allotrope they have dubbed [[Q-carbon]], created by a high-energy low-duration laser pulse on amorphous carbon dust. Q-carbon is reported to exhibit ferromagnetism, [[fluorescence]], and a hardness superior to diamonds.<ref>{{cite press release |title=Researchers find new phase of carbon, make diamond at room temperature |date=2015-11-30 |website=news.ncsu.edu |url=https://news.ncsu.edu/2015/11/narayan-q-carbon-2015/ |access-date=2016-04-06 |url-status=live |archive-url=https://web.archive.org/web/20160406002158/https://news.ncsu.edu/2015/11/narayan-q-carbon-2015/ |archive-date=2016-04-06}}</ref>

In the vapor phase, some of the carbon is in the form of highly reactive [[diatomic carbon]] dicarbon ({{chem2|C2}}). When excited, this gas glows green.<ref>{{cite journal | title = Chemistry of the singlet and triplet C<sub>2</sub> molecules. Mechanism of acetylene formation from reaction with acetone and acetaldehyde | first1 = Philip S. | last1 = Skell | author-link = Philip Skell | first2 = James H. | last2 = Plonka | journal = [[Journal of the American Chemical Society]] | year = 1970 | volume = 92 | issue = 19 | pages = 5620–5624| doi = 10.1021/ja00722a014| bibcode = 1970JAChS..92.5620S }}</ref><ref>{{cite journal |author1=J. Borsovszky |author2=K. Nauta |author3=J. Jiang |author4=C.S. Hansen |author5=L.K. McKemmish |author6=R.W. Field |author7=J.F. Stanton |author8=S.H. Kable |author9=T.W. Schmidt |title=Photodissociation of dicarbon: How nature breaks an unusual multiple bond |journal=Proceedings of the National Academy of Sciences of the United States of America |date=2021 |volume=118 |issue=52 |page=e2113315118 |doi=10.1073/pnas.2113315118 |doi-access=free |pmid=34930845 |pmc=8719853 |bibcode=2021PNAS..11813315B |language=en}}</ref>

===Occurrence===
[[File:GraphiteOreUSGOV.jpg|thumb|Graphite ore, shown with a penny for scale]]
[[File:Rough diamond.jpg|thumb|Raw diamond crystal]]
[[File:Annual mean sea surface dissolved inorganic carbon for the 1990s (GLODAP).png|thumb|"Present day" (1990s) sea surface [[dissolved inorganic carbon]] concentration (from the [[GLODAP]] [[climatology]])]]

Carbon is the [[abundance of the chemical elements|fourth most abundant chemical element]] in the observable universe by mass after hydrogen, helium, and oxygen. Carbon is abundant in the Sun, stars, comets, and in the [[celestial body's atmosphere|atmospheres]] of most planets.<ref name="Hoover-2014"/> Some [[meteorite]]s contain microscopic diamonds that were formed when the Solar System was still a [[protoplanetary disk]].<ref name="Lauretta-2006">{{cite book |last1=Lauretta |first1=D.S. |last2=McSween |first2=H.Y. |title=Meteorites and the Early Solar System II |publisher=University of Arizona Press |series=Space science series |year=2006 |isbn=978-0-8165-2562-1 |page=199 |url=https://books.google.com/books?id=FRc2iq9g9pkC&pg=PA199 |access-date=2017-05-07 |url-status=live |archive-url=https://web.archive.org/web/20171122173131/https://books.google.com/books?id=FRc2iq9g9pkC&pg=PA199 |archive-date=2017-11-22}}</ref> Microscopic diamonds may also be formed by the intense pressure and high temperature at the sites of meteorite impacts.<ref>{{cite book |author=Mark, Kathleen |url=https://archive.org/details/meteoritecraters0000mark_o3c4 |title=Meteorite Craters |date=1987 |publisher=University of Arizona Press |isbn=978-0-8165-0902-7 |url-access=registration}}</ref>

In 2014 [[NASA]] announced a [http://www.astrochem.org/pahdb/ greatly upgraded database] for tracking [[polycyclic aromatic hydrocarbons]] (PAHs) in the universe. More than 20% of the carbon in the universe may be associated with PAHs, complex compounds of carbon and hydrogen without oxygen.<ref>{{cite news |url=http://scitechdaily.com/online-database-tracks-organic-nano-particles-across-universe/ |title=Online Database Tracks Organic Nano-Particles Across the Universe |work=Sci Tech Daily |date=February 24, 2014 |access-date=2015-03-10 |url-status=live |archive-url=https://web.archive.org/web/20150318034957/http://scitechdaily.com/online-database-tracks-organic-nano-particles-across-universe/ |archive-date=March 18, 2015}}</ref> These compounds figure in the [[PAH world hypothesis]] where they are hypothesized to have a role in [[abiogenesis]] and formation of life. PAHs seem to have been formed "a couple of billion years" after the [[Big Bang]], are widespread throughout the universe, and are associated with [[star formation|new stars]] and [[exoplanet]]s.<ref name="Hoover-2014">{{cite web |last=Hoover |first=Rachel |title=Need to Track Organic Nano-Particles Across the Universe? NASA's Got an App for That |url=http://www.nasa.gov/ames/need-to-track-organic-nano-particles-across-the-universe-nasas-got-an-app-for-that/ |date=21 February 2014 |work=[[NASA]] |access-date=2014-02-22 |url-status=live |archive-url=https://web.archive.org/web/20150906061428/http://www.nasa.gov/ames/need-to-track-organic-nano-particles-across-the-universe-nasas-got-an-app-for-that/ |archive-date=6 September 2015}}</ref>

It has been estimated that the solid earth as a whole contains 730 ppm of carbon, with 2000 ppm in the core and 120 ppm in the combined mantle and crust.<ref>William F McDonough [http://quake.mit.edu/hilstgroup/CoreMantle/EarthCompo.pdf The composition of the Earth] {{webarchive|url=https://web.archive.org/web/20110928074153/http://quake.mit.edu/hilstgroup/CoreMantle/EarthCompo.pdf|date=2011-09-28}} in {{cite book |title=Earthquake Thermodynamics and Phase Transformation in the Earth's Interior |date=2000 |isbn=978-0-12-685185-4 |last1=Majewski |first1=Eugeniusz|publisher=Elsevier Science }}</ref> Since the mass of the earth is {{val|5.972|e=24|u=kg}}, this would imply 4360 million [[gigatonne]]s of carbon. This is much more than the amount of carbon in the oceans or atmosphere (below).

In combination with oxygen in carbon dioxide, carbon is found in the Earth's atmosphere (approximately 900&nbsp;gigatonnes of carbon — each ppm corresponds to 2.13&nbsp;Gt) and dissolved in all water bodies (approximately 36,000&nbsp;gigatonnes of carbon). Carbon in the [[biosphere]] has been estimated at 550&nbsp;gigatonnes but with a large uncertainty, due mostly to a huge uncertainty in the amount of terrestrial deep [[subsurface bacteria]].<ref>{{cite journal |display-authors=etal |last1=Yinon Bar-On |title=The biomass distribution on Earth |journal=[[PNAS]] |volume=115 |issue=25 |pages=6506–6511 |date=Jun 19, 2018 |doi=10.1073/pnas.1711842115 |pmid=29784790 |pmc=6016768 |bibcode=2018PNAS..115.6506B |doi-access=free}}</ref> [[Hydrocarbons]] (such as coal, petroleum, and natural gas) contain carbon as well. Coal "reserves" (not "resources") amount to around 900&nbsp;gigatonnes with perhaps 18,000 Gt of resources.<ref>{{cite journal |title=Fire in the hole: After fracking comes coal |journal=[[New Scientist]] |volume=221 |issue=2956 |date=2014-02-15 |pages=36–41 |url=https://www.newscientist.com/article/mg22129560.400-fire-in-the-hole-after-fracking-comes-coal.html?full=true |author=Fred Pearce |author-link=Fred Pearce |url-status=live |archive-url=https://web.archive.org/web/20150316021625/http://www.newscientist.com/article/mg22129560.400-fire-in-the-hole-after-fracking-comes-coal.html?full=true |archive-date=2015-03-16 |bibcode=2014NewSc.221...36P |doi=10.1016/S0262-4079(14)60331-6}}</ref> [[Oil reserves]] are around 150&nbsp;gigatonnes. Proven sources of natural gas are about {{val|175|e=12|u=cubic metres}} (containing about 105 gigatonnes of carbon), but studies estimate another {{val|900|e=12|u=cubic metres}} of "unconventional" deposits such as [[shale gas]], representing about 540 gigatonnes of carbon.<ref>[https://www.newscientist.com/article/mg20627641.100-wonderfuel-welcome-to-the-age-of-unconventional-gas.html?full=true "Wonderfuel: Welcome to the age of unconventional gas"] {{webarchive|url=https://web.archive.org/web/20141209231648/http://www.newscientist.com/article/mg20627641.100-wonderfuel-welcome-to-the-age-of-unconventional-gas.html?full=true|date=2014-12-09}} by Helen Knight, ''[[New Scientist]]'', 12 June 2010, pp. 44–7.</ref>

Carbon is also found in [[methane hydrates]] in polar regions and under the seas. Various estimates put this carbon between 500, 2500,<ref>[http://news.bbc.co.uk/2/hi/science/nature/3493349.stm Ocean methane stocks 'overstated'] {{webarchive|url=https://web.archive.org/web/20130425211445/http://news.bbc.co.uk/2/hi/science/nature/3493349.stm|date=2013-04-25}}, BBC, 17 Feb. 2004.</ref> or 3,000 Gt.<ref>[https://www.newscientist.com/article/mg20227141.100 "Ice on fire: The next fossil fuel"] {{webarchive|url=https://web.archive.org/web/20150222041938/http://www.newscientist.com/article/mg20227141.100|date=2015-02-22}} by [[Fred Pearce]], ''New Scientist'', 27 June 2009, pp. 30–33.</ref>

According to one source, in the period from 1751 to 2008 about 347 gigatonnes of carbon were released as carbon dioxide to the atmosphere from burning of fossil fuels.<ref>Calculated from file global.1751_2008.csv in {{cite web |url=http://cdiac.ornl.gov/ftp/ndp030/CSV-FILES |title=Index of /ftp/ndp030/CSV-FILES |access-date=2011-11-06 |url-status=dead |archive-url=https://web.archive.org/web/20111022125534/http://cdiac.ornl.gov/ftp/ndp030/CSV-FILES/ |archive-date=2011-10-22}} from the [[Carbon Dioxide Information Analysis Center]].</ref> Another source puts the amount added to the atmosphere for the period since 1750 at 879 Gt, and the total going to the atmosphere, sea, and land (such as [[peat bog]]s) at almost 2,000 Gt.<ref>{{cite journal |title=Deep, and dank mysterious |journal=New Scientist |date=Sep 21, 2013 |pages=40–43 |url=https://www.newscientist.com/articleimages/mg21929350.800/1-whats-brown-and-soggy-and-could-save-the-world.html |author=Rachel Gross |url-status=live |archive-url=https://web.archive.org/web/20130921055409/http://www.newscientist.com/articleimages/mg21929350.800/1-whats-brown-and-soggy-and-could-save-the-world.html |archive-date=2013-09-21}}</ref>

Carbon is a constituent (about 12% by mass) of the very large masses of [[carbonate]] rock ([[limestone]], [[dolomite (mineral)|dolomite]], [[marble]], and others). Coal is very rich in carbon ([[anthracite]] contains 92–98%)<ref>{{cite book |title=Coal Mining Technology: Theory and Practice |author=Stefanenko, R. |publisher=Society for Mining Metallurgy |date=1983 |isbn=978-0-89520-404-2}}</ref> and is the largest commercial source of mineral carbon, accounting for 4,000&nbsp;gigatonnes or 80% of [[fossil fuel]].<ref>{{cite journal |first=James |last=Kasting |date=1998 |title=The Carbon Cycle, Climate, and the Long-Term Effects of Fossil Fuel Burning |journal=Consequences: The Nature and Implication of Environmental Change |volume=4 |issue=1 |url=http://gcrio.org/CONSEQUENCES/vol4no1/carbcycle.html |url-status=live |archive-url=https://web.archive.org/web/20081024152448/http://gcrio.org/CONSEQUENCES/vol4no1/carbcycle.html |archive-date=2008-10-24}}</ref>

As for individual carbon allotropes, graphite is found in large quantities in China, Russia, Mexico, Canada, and India.<ref>{{cite book |author1=Wilhelm Frohs |author2=Ferdinand von Sturm |author3=Erhard Wege |author4=Gabriele Nutsch |author5=Werner Handl |title=Ullmann's Encyclopedia of Industrial Chemistry |date=2010 |isbn=9783527306732 |chapter=Carbon, 3. Graphite|publisher=Wiley }}</ref> Natural diamonds occur in the rock [[kimberlite]], found in ancient volcanic "necks", or "pipes". Most diamond deposits are in Africa, notably in South Africa, Namibia, Botswana, the Republic of the Congo, and Angola. Diamond deposits have also been found in [[Arkansas]], Canada, the Russian Arctic, Brazil, and in Northern and Western Australia.<ref>{{cite book |author1=Otto Vohler |author2=Gabriele Nutsch |author3=Ferdinand von Sturm |author4=Erhard Wege |title=Ullmann's Encyclopedia of Industrial Chemistry |date=2010 |isbn=9783527306732 |language=en |chapter=Carbon, 2. Diamond |doi=10.1002/14356007.n05_n01}}</ref> Diamonds are found naturally, but about 90% of all industrial diamonds used in the U.S. are now manufactured.<ref>{{cite web |author1=Donald Olson |title=Industrial Diamond Statistics and Information |url=https://www.usgs.gov/centers/national-minerals-information-center/industrial-diamond-statistics-and-information |website=USGS |publisher=National Minerals Information Center |language=en}}</ref>

Carbon-14 is formed in upper layers of the troposphere and the stratosphere at altitudes of 9–15&nbsp;km by a reaction that is precipitated by [[cosmic ray]]s.<ref>{{cite web |url=http://www.acad.carleton.edu/curricular/BIOL/classes/bio302/pages/carbondatingback.html |url-status=live |title=Carbon-14 formation |access-date=13 October 2014 |archive-url=https://web.archive.org/web/20150801234723/http://www.acad.carleton.edu/curricular/BIOL/classes/bio302/pages/carbondatingback.html |archive-date=1 August 2015}}</ref> [[Thermal neutron]]s are produced that collide with the nuclei of nitrogen-14, forming carbon-14 and a proton. As such, {{val|1.5|e=-10|u=%}} of atmospheric carbon dioxide contains carbon-14.<ref>{{cite book |last1=Aitken |first1=M.J. |title=Science-based Dating in Archaeology |date=1990 |isbn=978-0-582-49309-4 |pages=56–58|publisher=Longman }}</ref>

Carbon-rich asteroids are relatively preponderant in the outer parts of the [[asteroid belt]] in the Solar System. These asteroids have not yet been directly sampled by scientists. The asteroids can be used in hypothetical [[asteroid mining|space-based carbon mining]], which may be possible in the future, but is currently technologically impossible.<ref>{{cite web |last1=Nichols |first1=Charles R. |title=Voltatile Products from Carbonaceous Asteroids |url=http://www.uapress.arizona.edu/onlinebks/ResourcesNearEarthSpace/resources21.pdf |website=UAPress.Arizona.edu |access-date=12 November 2016 |url-status=dead |archive-url=https://web.archive.org/web/20160702023807/http://www.uapress.arizona.edu/onlinebks/ResourcesNearEarthSpace/resources21.pdf |archive-date=2 July 2016 |df=dmy-all}}</ref>

===Isotopes===
{{Main|Isotopes of carbon}}
[[Isotope]]s of carbon are [[atomic nuclei]] that contain six [[proton]]s plus a number of [[neutron]]s (varying from 2 to 16). Carbon has two stable, naturally occurring isotopes.<ref name="WebElements">{{cite web |url=http://www.webelements.com/webelements/elements/text/C/isot.html |title=Carbon&nbsp;– Naturally occurring isotopes |publisher=WebElements Periodic Table |access-date=2008-10-09 |url-status=live |archive-url=https://web.archive.org/web/20080908030327/http://www.webelements.com/webelements/elements/text/C/isot.html |archive-date=2008-09-08}}</ref> The isotope [[carbon-12]] ({{sup|12}}C) forms 98.93% of the carbon on Earth, while [[carbon-13]] ({{sup|13}}C) forms the remaining 1.07%.<ref name="WebElements" /> The concentration of {{sup|12}}C is further increased in biological materials because biochemical reactions discriminate against {{sup|13}}C.<ref>{{cite journal |last1=Gannes |first1=Leonard Z. |last2=Del Rio |first2=Carlos Martı́nez |last3=Koch |first3=Paul |title=Natural Abundance Variations in Stable Isotopes and their Potential Uses in Animal Physiological Ecology |journal=Comparative Biochemistry and Physiology&nbsp;– Part A: Molecular & Integrative Physiology |volume=119 |issue=3 |pages=725–737 |date=1998 |doi=10.1016/S1095-6433(98)01016-2 |pmid=9683412}}</ref> In 1961, the [[International Union of Pure and Applied Chemistry]] (IUPAC) adopted the isotope carbon-12 as the basis for [[atomic weight]]s.<ref>{{cite web |url=http://www.bipm.org/en/si/base_units/ |title=Official SI Unit definitions |access-date=2007-12-21 |url-status=live |archive-url=https://web.archive.org/web/20071014094602/http://www.bipm.org/en/si/base_units/ |archive-date=2007-10-14}}</ref> Identification of carbon in [[nuclear magnetic resonance]] (NMR) experiments is done with the isotope {{sup|13}}C.

[[Carbon-14]] ({{sup|14}}C) is a naturally occurring [[radioisotope]], created in the [[upper atmosphere]] (lower [[stratosphere]] and upper [[troposphere]]) by interaction of nitrogen with cosmic rays.<ref>{{cite book |first=S. |last=Bowman |date=1990 |title=Interpreting the past: Radiocarbon dating |publisher=British Museum Press |isbn=978-0-7141-2047-8}}</ref> It is found in trace amounts on Earth of 1 part per [[10^12|trillion]] (0.0000000001%) or more, mostly confined to the atmosphere and superficial deposits, particularly of peat and other organic materials.<ref>{{cite web |last=Brown |first=Tom |date=March 1, 2006 |url=http://www.llnl.gov/str/March06/Brown.html |title=Carbon Goes Full Circle in the Amazon |publisher=Lawrence Livermore National Laboratory |access-date=2007-11-25 |url-status=live |archive-url=https://web.archive.org/web/20080922031202/https://www.llnl.gov/str/March06/Brown.html |archive-date=September 22, 2008}}</ref> This isotope decays by 0.158&nbsp;MeV [[beta decay|β{{sup|−}} emission]]. Because of its relatively short [[half-life]] of {{val|5700|30}}&nbsp;years,{{NUBASE2020|name}} {{sup|14}}C is virtually absent in ancient rocks. The amount of {{sup|14}}C in the [[atmosphere]] and in living organisms is almost constant, but decreases predictably in their bodies after death. This principle is used in [[radiocarbon dating]], invented in 1949, which has been used extensively to determine the age of carbonaceous materials with ages up to about 40,000&nbsp;years.<ref>{{cite book |last=Libby |first=W. F. |date=1952 |title=Radiocarbon dating |publisher=Chicago University Press and references therein}}</ref><ref>{{cite web |last=Westgren |first=A. |date=1960 |url=http://nobelprize.org/nobel_prizes/chemistry/laureates/1960/press.html |title=The Nobel Prize in Chemistry 1960 |publisher=Nobel Foundation |access-date=2007-11-25 |url-status=live |archive-url=https://web.archive.org/web/20071025003508/http://nobelprize.org/nobel_prizes/chemistry/laureates/1960/press.html |archive-date=2007-10-25}}</ref>

There are 15 known isotopes of carbon and the shortest-lived of these is {{sup|8}}C which decays through [[proton emission]] and has a half-life of 3.5{{e|−21}} s.{{NUBASE2020|ref}} The exotic {{sup|19}}C exhibits a [[nuclear halo]], which means its radius is appreciably larger than would be expected if the nucleus were a sphere of constant density.<ref>{{cite journal |title=Beaming Into the Dark Corners of the Nuclear Kitchen |last1=Watson |first1=A. |journal=Science |volume=286 |issue=5437 |pages=28–31 |date=1999 |s2cid=117737493 |doi=10.1126/science.286.5437.28}}</ref>

===Formation in stars===
{{Main|Triple-alpha process|CNO cycle}}
Formation of the carbon atomic nucleus occurs within a [[giant star|giant]] or [[supergiant]] star through the [[triple-alpha process]]. This requires a nearly simultaneous collision of three [[alpha particle]]s (helium nuclei), as the products of further [[nuclear fusion]] reactions of helium with hydrogen or another helium nucleus produce [[isotopes of lithium|lithium-5]] and [[isotopes of beryllium|beryllium-8]] respectively, both of which are highly unstable and decay almost instantly back into smaller nuclei.<ref name="Audi-1997">{{NUBASE 1997}}</ref> The triple-alpha process happens in conditions of temperatures over 100 megakelvins and helium concentration that the rapid expansion and cooling of the early universe prohibited, and therefore no significant carbon was created during the Big Bang.<ref>{{cite book|last1=Wilson|first1=Robert|title=Astronomy through the ages the story of the human attempt to understand the universe|date=1997|publisher=[[Taylor & Francis]]|location=Basingstoke|isbn=9780203212738|chapter=Chapter 11: The Stars – their Birth, Life, and Death}}</ref>

According to current physical cosmology theory, carbon is formed in the interiors of stars on the [[horizontal branch]].<ref name="Ostlie-2007">{{cite book |last1=Ostlie |first1=Dale A. |last2=Carroll |first2=Bradley W. |name-list-style=amp |title=An Introduction to Modern Stellar Astrophysics |publisher=Addison Wesley |location=San Francisco (CA) |date=2007 |isbn=978-0-8053-0348-3}}</ref> When massive stars die as supernova, the carbon is scattered into space as dust. This dust becomes component material for the formation of the next-generation star systems with accreted planets.<ref name="Hoover-2014"/><ref>{{cite book |last=Whittet |first=Douglas C. B. |date=2003 |title=Dust in the Galactic Environment |pages=45–46 |publisher=[[CRC Press]] |isbn=978-0-7503-0624-9}}</ref> The Solar System is one such star system with an abundance of carbon, enabling the existence of life as we know it. It is the opinion of most scholars that all the carbon in the Solar System and the [[Milky Way]] comes from dying stars.<ref name="Bohan-2016">{{cite book |last1=Bohan |first1=Elise |url=https://www.worldcat.org/oclc/940282526 |title=Big History |last2=Dinwiddie |first2=Robert |last3=Challoner |first3=Jack |last4=Stuart |first4=Colin |last5=Harvey |first5=Derek |last6=Wragg-Sykes |first6=Rebecca |last7=Chrisp |first7=Peter |last8=Hubbard |first8=Ben |last9=Parker |first9=Phillip |collaboration=Writers |date=February 2016 |publisher=[[DK (publisher)|DK]] |others=Foreword by [[David Christian (historian)|David Christian]] |isbn=978-1-4654-5443-0 |edition=1st American |location=[[New York City|New York]] |pages=10–11, 45, 55, 58–59, 63, 65–71, 75, 78–81, 98, 100, 102 |oclc=940282526 |author-link6=Rebecca Wragg Sykes |author-link7=Peter Chrisp}}</ref><ref>{{cite web |date=May 2003 |title=Is my body really made up of star stuff? |url=https://starchild.gsfc.nasa.gov/docs/StarChild/questions/question57.html |access-date=2023-03-17 |publisher=[[NASA]]}}</ref><ref>{{cite web |last=Firaque |first=Kabir |date=2020-07-10 |title=Explained: How stars provided the carbon that makes life possible |url=https://indianexpress.com/article/explained/explained-how-the-stars-provided-the-carbon-that-makes-life-possible-6499596/ |access-date=2023-03-17 |website=[[The Indian Express]] |language=en}}</ref>

The [[CNO cycle]] is an additional hydrogen fusion mechanism that powers stars, wherein carbon operates as a catalyst.

Rotational transitions of various isotopic forms of carbon monoxide (for example, {{sup|12}}CO, {{sup|13}}CO, and {{sup|18}}CO) are detectable in the [[submillimeter]] wavelength range, and are used in the study of newly forming stars in [[molecular cloud]]s.<ref>{{cite book |last=Pikelʹner |first=Solomon Borisovich |title=Star Formation |url=https://books.google.com/books?id=qbGLgcxnfpIC&pg=PA38 |access-date=2011-06-06 |date=1977 |publisher=Springer |isbn=978-90-277-0796-3 |pages=38 |url-status=live |archive-url=https://web.archive.org/web/20121123220424/http://books.google.com/books?id=qbGLgcxnfpIC&pg=PA38 |archive-date=2012-11-23}}</ref>

===Carbon cycle===
{{Main|Carbon cycle}}
[[File:Carbon cycle-cute diagram.svg|thumb|upright=1.35|Diagram of the carbon cycle. The black numbers indicate how much carbon is stored in various reservoirs, in billions tonnes ("GtC" stands for gigatonnes of carbon; figures are {{Circa|2004}}). The purple numbers indicate how much carbon moves between reservoirs each year. The sediments, as defined in this diagram, do not include the ≈70&nbsp;million GtC of carbonate rock and [[kerogen]].]]

Under terrestrial conditions, conversion of one element to another is very rare. Therefore, the amount of carbon on Earth is effectively constant. Thus, processes that use carbon must obtain it from somewhere and dispose of it somewhere else. The paths of carbon in the environment form the [[carbon cycle]].<ref>Mannion, pp. 51–54.</ref> For example, [[photosynthetic]] plants draw carbon dioxide from the atmosphere (or seawater) and build it into biomass, as in the [[Calvin cycle]], a process of [[carbon fixation]].<ref>Mannion, pp. 84–88.</ref> Some of this biomass is eaten by animals, while some carbon is exhaled by animals as carbon dioxide. The carbon cycle is considerably more complicated than this short loop; for example, some carbon dioxide is dissolved in the oceans; if bacteria do not consume it, dead plant or animal matter may become petroleum or coal, which releases carbon when burned.<ref>{{cite journal |journal=Science |date=2000 |volume=290 |issue=5490 |pages=291–296 |doi=10.1126/science.290.5490.291 |s2cid=1779934 |bibcode=2000Sci...290..291F |pmid=11030643 |title=The Global Carbon Cycle: A Test of Our Knowledge of Earth as a System |last1=Falkowski |first1=P. |last2=Scholes |first2=R. J. |last3=Boyle |first3=E. |last4=Canadell |first4=J. |last5=Canfield |first5=D. |last6=Elser |first6=J. |last7=Gruber |first7=N. |last8=Hibbard |first8=K. |last9=Högberg |first9=P. |display-authors=8}}</ref><ref>{{cite journal |title=The global terrestrial carbon cycle |date=1993 |last1=Smith |first1=T. M. |last2=Cramer |first2=W. P. |last3=Dixon |first3=R. K. |last4=Leemans |first4=R. |last5=Neilson |first5=R. P. |last6=Solomon |first6=A. M. |journal=Water, Air, & Soil Pollution |volume=70 |issue=1–4 |pages=19–37 |bibcode=1993WASP...70...19S |s2cid=97265068 |doi=10.1007/BF01104986 |url=https://hal-amu.archives-ouvertes.fr/hal-01788303/file/Smith1993.pdf |archive-url=https://web.archive.org/web/20221011170500/https://hal-amu.archives-ouvertes.fr/hal-01788303/file/Smith1993.pdf |archive-date=2022-10-11 |url-status=live}}</ref>

==Compounds==
{{Main|Carbon compounds}}

===Organic compounds===
[[File:Methane-2D-stereo.svg|thumb|left|upright=0.7|Structural formula of [[methane]], the simplest possible organic compound.]]
[[File:Auto-and heterotrophs.png|thumb|upright=1.35|Correlation between the ''carbon cycle'' and formation of organic compounds. In plants, carbon dioxide formed by carbon fixation can join with water in [[photosynthesis]] (<span style="color:green;">green</span>) to form organic compounds, which can be used and further converted by both plants and animals.]]
Carbon can form very long chains of interconnecting [[carbon–carbon bond]]s, a property that is called [[catenation]]. Carbon-carbon bonds are strong and stable. Through [p[catenation, carbon forms a countless number of compounds. A tally of unique compounds shows that more contain carbon than do not.<ref name="Burrows-2017">{{cite book |last1=Burrows |first1=A. |last2=Holman |first2=J. |last3=Parsons |first3=A. |last4=Pilling |first4=G. |last5=Price |first5=G. |title=Chemistry3: Introducing Inorganic, Organic and Physical Chemistry |publisher=Oxford University Press |year=2017 |isbn=978-0-19-873380-5 |page=70 |url=https://books.google.com/books?id=YzbjDQAAQBAJ&pg=PA70 |access-date=2017-05-07 |url-status=live |archive-url=https://web.archive.org/web/20171122173131/https://books.google.com/books?id=YzbjDQAAQBAJ&pg=PA70 |archive-date=2017-11-22}}</ref>

The simplest form of an organic molecule is the hydrocarbon—a large family of organic molecules that are composed of hydrogen atoms bonded to a chain of carbon atoms. A hydrocarbon backbone can be substituted by other atoms, known as [[heteroatom]]s. Common heteroatoms that appear in organic compounds include oxygen, nitrogen, sulfur, phosphorus, and the nonradioactive halogens, as well as the metals lithium and magnesium. Organic compounds containing bonds to metal are known as organometallic compounds (''see below''). Certain groupings of atoms, often including heteroatoms, recur in large numbers of organic compounds. These collections, known as ''[[functional group]]s'', confer common reactivity patterns and allow for the systematic study and categorization of organic compounds. Chain length, shape and functional groups all affect the properties of organic molecules.<ref>Mannion pp. 27–51</ref>

In most stable compounds of carbon (and nearly all stable ''organic'' compounds), carbon obeys the [[octet rule]] and is ''tetravalent'', meaning that a carbon atom forms a total of four covalent bonds (which may include double and triple bonds). Exceptions include a small number of stabilized ''carbocations'' (three bonds, positive charge), ''radicals'' (three bonds, neutral), ''carbanions'' (three bonds, negative charge) and ''carbenes'' (two bonds, neutral), although these species are much more likely to be encountered as unstable, reactive intermediates.<ref name="Claydentext">{{Clayden}}</ref>

Carbon occurs in all known organic life and is the basis of [[organic chemistry]]. When united with hydrogen, it forms various hydrocarbons that are important to industry as refrigerants, lubricants, solvents, as chemical feedstock for the manufacture of plastics and petrochemicals, and as fossil fuels.<ref name="Claydentext" />

When combined with oxygen and hydrogen, carbon can form many groups of important biological compounds including sugars, [[lignan]]s, [[chitin]]s, alcohols, fats, aromatic [[ester]]s, [[carotenoid]]s and [[terpene]]s. With nitrogen, it forms [[alkaloid]]s, and with the addition of sulfur also it forms antibiotics, [[amino acid]]s, and rubber products. With the addition of phosphorus to these other elements, it forms [[DNA]] and [[RNA]], the chemical-code carriers of life, and [[adenosine triphosphate]] (ATP), the most important energy-transfer molecule in all living cells.<ref>Mannion pp. 84–91</ref>  [[Norman Horowitz]], head of the [[Viking program|Mariner and Viking missions to Mars]] (1965–1976), considered that the unique characteristics of carbon made it unlikely that any other element could replace carbon, even on another planet, to generate the biochemistry necessary for life.<ref>Norman H. Horowitz (1986) To Utopia and Back; the search for life in the solar system (Astronomy Series) W. H. Freeman & Co (Sd), NY, {{ISBN|978-0-7167-1766-9}}</ref>

===Inorganic compounds===
Commonly carbon-containing compounds which are associated with minerals or which do not contain bonds to the other carbon atoms, halogens, or hydrogen, are treated separately from classical organic compounds; the definition is not rigid, and the classification of some compounds can vary from author to author (see reference articles above). Among these are the simple oxides of carbon. The most prominent oxide is carbon dioxide ({{CO2}}). This was once the principal constituent of the [[paleoatmosphere]], but is a minor component of the [[Earth's atmosphere]] today.<ref>{{cite journal |date=1982 |title=The prebiological paleoatmosphere: stability and composition |journal=Origins of Life and Evolution of Biospheres |volume=12 |pages=245–259 |doi=10.1007/BF00926894 |pmid=7162799 |issue=3 |bibcode=1982OrLi...12..245L |s2cid=20097153 |last1=Levine |first1=Joel S. |last2=Augustsson |first2=Tommy R. |last3=Natarajan |first3=Murali}}</ref> Dissolved in water, it forms [[carbonic acid]] ({{chem|H|2|C|O|3}}), but as most compounds with multiple single-bonded oxygens on a single carbon it is unstable.<ref>{{cite journal |author=Loerting, T. |author1-link=Thomas Loerting |date=2001 |title=On the Surprising Kinetic Stability of Carbonic Acid |journal=Angew. Chem. Int. Ed. |volume=39 |pages=891–895 |doi=10.1002/(SICI)1521-3773(20000303)39:5<891::AID-ANIE891>3.0.CO;2-E |pmid=10760883 |issue=5 |display-authors=1 |last2=Tautermann |first2=Christofer |last3=Kroemer |first3=Romano T. |last4=Kohl |first4=Ingrid |last5=Hallbrucker |first5=Andreas |last6=Mayer |first6=Erwin |last7=Liedl |first7=Klaus R.}}</ref> Through this intermediate, though, resonance-stabilized carbonate [[ion]]s are produced. Some important minerals are carbonates, notably [[calcite]]. [[Carbon disulfide]] ({{chem|C|S|2}}) is similar.{{sfn|Greenwood|Earnshaw|1997|pages=289-292}}

The other common oxide is carbon monoxide (CO). It is formed by incomplete combustion, and is a colorless, odorless gas. The molecules each contain a triple bond and are fairly [[polar molecule|polar]], resulting in a tendency to bind permanently to hemoglobin molecules, displacing oxygen, which has a lower binding affinity.<ref>{{cite journal |author=Haldane J. |date=1895 |title=The action of carbonic oxide on man |journal=Journal of Physiology |volume=18 |pages=430–462 |pmid=16992272 |issue=5–6 |pmc=1514663 |doi=10.1113/jphysiol.1895.sp000578}}</ref><ref>{{cite journal |date=2003 |title=The clinical toxicology of carbon monoxide |journal=Toxicology |issue=1 |pages=25–38 |volume=187 |pmid=12679050 |doi=10.1016/S0300-483X(03)00005-2 |last1=Gorman |first1=D. |last2=Drewry |first2=A. |last3=Huang |first3=Y. L. |last4=Sames |first4=C.|bibcode=2003Toxgy.187...25G }}</ref> [[Cyanide]] (CN{{sup|−}}), has a similar structure, but behaves much like a [[halide]] ion ([[pseudohalogen]]). For example, it can form the nitride [[cyanogen]] molecule ((CN){{sub|2}}), similar to diatomic halides. Likewise, the heavier analog of cyanide, [[cyaphide]] (CP{{sup|−}}), is also considered inorganic, though most simple derivatives are highly unstable. Other uncommon oxides are [[carbon suboxide]] ({{chem|C|3|O|2}}),<ref>{{cite web |title=Compounds of carbon: carbon suboxide |url=http://www.webelements.com/webelements/compounds/text/C/C3O2-504643.html |access-date=2007-12-03 |url-status=live |archive-url=https://web.archive.org/web/20071207230312/http://www.webelements.com/webelements/compounds/text/C/C3O2-504643.html |archive-date=2007-12-07}}</ref> the unstable [[dicarbon monoxide]] (C{{sub|2}}O),<ref>{{cite journal |last1=Bayes |first1=K. |title=Photolysis of Carbon Suboxide |journal=[[Journal of the American Chemical Society]] |volume=83 |date=1961 |pages=3712–3713 |doi=10.1021/ja01478a033 |issue=17|bibcode=1961JAChS..83.3712B }}</ref><ref>{{cite journal |author=Anderson D. J. |title=Photodissociation of Carbon Suboxide |journal=[[Journal of Chemical Physics]] |volume=94 |date=1991 |pages=7852–7867 |issue=12 |bibcode=1991JChPh..94.7857A |doi=10.1063/1.460121 |last2=Rosenfeld |first2=R. N.}}</ref> [[carbon trioxide]] (CO{{sub|3}}),<ref>{{cite journal |title=A theoretical study of the structure and properties of carbon trioxide |last1=Sabin |first1=J. R. |journal=[[Chemical Physics Letters]] |volume=11 |issue=5 |pages=593–597 |date=1971 |doi=10.1016/0009-2614(71)87010-0 |bibcode=1971CPL....11..593S |last2=Kim |first2=H.}}</ref><ref>{{cite journal |title=Carbon Trioxide: Its Production, Infrared Spectrum, and Structure Studied in a Matrix of Solid CO{{sub |2}} |journal=Journal of Chemical Physics|date=1966|volume=45|issue=12|pages=4469–4481|doi=10.1063/1.1727526|bibcode=1966JChPh..45.4469M |author=Moll N. G.|author2=Clutter D. R.|author3=Thompson W. E.}}</ref> [[cyclopentanepentone]] (C{{sub|5}}O{{sub|5}}),<ref name="Fatiadi-1963">{{cite journal |title=Cyclic Polyhydroxy Ketones. I. Oxidation Products of Hexahydroxybenzene (Benzenehexol) |journal=Journal of Research of the National Bureau of Standards Section A |volume=67A |issue=2 |date=1963 |pages=153–162 |url=http://nvl.nist.gov/pub/nistpubs/jres/067/2/V67.N02.A06.pdf |url-status=dead |access-date=2009-03-21 |doi=10.6028/jres.067A.015 |pmid=31580622 |pmc=6640573 |first1=Alexander J. |last1=Fatiadi |last2=Isbell |first2=Horace S. |last3=Sager |first3=William F. |archive-url=https://web.archive.org/web/20090325204012/http://nvl.nist.gov/pub/nistpubs/jres/067/2/V67.N02.A06.pdf |archive-date=2009-03-25}}</ref> [[cyclohexanehexone]] (C{{sub|6}}O{{sub|6}}),<ref name="Fatiadi-1963"/> and [[mellitic anhydride]] (C{{sub|12}}O{{sub|9}}). However, mellitic anhydride is the triple acyl anhydride of mellitic acid; moreover, it contains a benzene ring. Thus, many chemists consider it to be organic.

With reactive metals, such as [[tungsten]], carbon forms either [[carbide]]s (C{{sup|4−}}) or [[acetylide]]s ({{chem|C|2|2-}}) to form alloys with high melting points. These anions are also associated with methane and [[acetylene]], both very weak acids. With an electronegativity of 2.5,<ref>{{cite book |first=L. |last=Pauling |title=The Nature of the Chemical Bond |url=https://archive.org/details/natureofchemical00paul |url-access=registration |edition=3rd |publisher=Cornell University Press |location=Ithaca, NY |date=1960 |page=[https://archive.org/details/natureofchemical00paul/page/93 93] |isbn=978-0-8014-0333-0}}</ref> carbon prefers to form [[covalent bond]]s. A few carbides are covalent lattices, like [[carborundum]] (SiC), which resembles diamond. Nevertheless, even the most polar and salt-like of carbides are not completely ionic compounds.{{sfn|Greenwood|Earnshaw|1997|pages=297-301}}

===Organometallic compounds===
{{Main|Organometallic chemistry}}
Organometallic compounds by definition contain at least one carbon-metal covalent bond. A wide range of such compounds exist; major classes include simple alkyl-metal compounds (for example, [[tetraethyllead]]), η{{sup|2}}-alkene compounds (for example, [[Zeise's salt]]), and η{{sup|3}}-allyl compounds (for example, [[allylpalladium chloride dimer]]); [[metallocene]]s containing cyclopentadienyl ligands (for example, [[ferrocene]]); and [[transition metal carbene complex]]es. Many [[metal carbonyl]]s and [[cyanometalate|metal cyanides]] exist (for example, [[tetracarbonylnickel]] and [[potassium ferricyanide]]); some workers consider metal carbonyl and cyanide complexes without other carbon ligands to be purely inorganic, and not organometallic. However, most organometallic chemists consider metal complexes with any carbon ligand, even 'inorganic carbon' (e.g., carbonyls, cyanides, and certain types of carbides and acetylides) to be organometallic in nature. Metal complexes containing organic ligands without a carbon-metal covalent bond (e.g., metal carboxylates) are termed ''metalorganic'' compounds.

While carbon is understood to strongly prefer formation of four covalent bonds, other exotic bonding schemes are also known. [[Carborane]]s are highly stable dodecahedral derivatives of the [B<sub>12</sub>H<sub>12</sub>]<sup>2-</sup> unit, with one BH replaced with a CH<sup>+</sup>. Thus, the carbon is bonded to five boron atoms and one hydrogen atom. The cation [(Ph{{sub|3}}PAu){{sub|6}}C]{{sup|2+}} contains an octahedral carbon bound to six phosphine-gold fragments. This phenomenon has been attributed to the [[aurophilicity]] of the gold ligands, which provide additional stabilization of an otherwise labile species.<ref>{{cite journal |author=Scherbaum, Franz |journal=[[Angew. Chem. Int. Ed. Engl.]] |volume=27 |issue=11 |pages=1544–1546 |date=1988 |doi=10.1002/anie.198815441 |title="Aurophilicity" as a consequence of Relativistic Effects: The Hexakis(triphenylphosphaneaurio)methane Dication [(Ph{{sub |3}}PAu){{sub|6}}C]{{sup|2+}} |display-authors=1|last2=Grohmann|first2=Andreas|last3=Huber|first3=Brigitte|last4=Krüger|first4=Carl|last5=Schmidbaur|first5=Hubert}}</ref> In nature, the iron-molybdenum cofactor ([[FeMoco]]) responsible for microbial [[nitrogen fixation]] likewise has an octahedral carbon center (formally a carbide, C(-IV)) bonded to six iron atoms. In 2016, it was confirmed that, in line with earlier theoretical predictions, the [[hexamethylbenzene|hexamethylbenzene dication]] contains a carbon atom with six bonds. More specifically, the dication could be described structurally by the formulation [MeC(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)]<sup>2+</sup>, making it an "organic [[metallocene]]" in which a MeC<sup>3+</sup> fragment is bonded to a η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub><sup>−</sup> fragment through all five of the carbons of the ring.<ref>{{cite magazine |url=http://cen.acs.org/articles/94/i49/Six-bonds-carbon-Confirmed.html?type=paidArticleContent |url-status=live |title=Six bonds to carbon: Confirmed |first=Stephen K. |last=Ritter |magazine=Chemical & Engineering News |archive-url=https://web.archive.org/web/20170109183800/http://cen.acs.org/articles/94/i49/Six-bonds-carbon-Confirmed.html?type=paidArticleContent |archive-date=2017-01-09}}</ref>

[[File:Akiba's "hypervalent carbon" compound.png|thumb|This anthracene derivative contains a carbon atom with 5 formal electron pairs around it.]]
It is important to note that in the cases above, each of the bonds to carbon contain less than two formal electron pairs. Thus, the formal electron count of these species does not exceed an octet. This makes them hypercoordinate but not hypervalent. Even in cases of alleged 10-C-5 species (that is, a carbon with five ligands and a formal electron count of ten), as reported by Akiba and co-workers,<ref>{{cite journal |last1=Yamashita |first1=Makoto |last2=Yamamoto |first2=Yohsuke |last3=Akiba |first3=Kin-ya |last4=Hashizume |first4=Daisuke |last5=Iwasaki |first5=Fujiko |last6=Takagi |first6=Nozomi |last7=Nagase |first7=Shigeru |date=2005-03-01 |title=Syntheses and Structures of Hypervalent Pentacoordinate Carbon and Boron Compounds Bearing an Anthracene Skeleton − Elucidation of Hypervalent Interaction Based on X-ray Analysis and DFT Calculation |journal=Journal of the American Chemical Society |volume=127 |issue=12 |pages=4354–4371 |doi=10.1021/ja0438011 |pmid=15783218 |bibcode=2005JAChS.127.4354Y |issn=0002-7863}}</ref> electronic structure calculations conclude that the electron population around carbon is still less than eight, as is true for other compounds featuring four-electron [[three-center bond]]ing.

==History and etymology==
[[File:Antoine lavoisier.jpg|thumb|upright|left|[[Antoine Lavoisier]] in his youth]]
The English name ''carbon'' comes from the Latin ''carbo'' for coal and charcoal,<ref>Shorter Oxford English Dictionary, Oxford University Press</ref> whence also comes the French ''charbon'', meaning charcoal. In German, Dutch and Danish, the names for carbon are ''Kohlenstoff'', ''koolstof'', and ''kulstof'' respectively, all literally meaning coal-substance.

Carbon was discovered in prehistory and was known in the forms of soot and charcoal to the earliest human civilizations. Diamonds were known probably as early as 2500&nbsp;BCE in China, while carbon in the form of charcoal was made by the same chemistry as it is today, by heating wood in a pyramid covered with clay to exclude air.<ref name="BBCNews-2005">{{cite news |url=http://news.bbc.co.uk/2/hi/science/nature/4555235.stm |title=Chinese made first use of diamond |work=BBC News |date=17 May 2005 |access-date=2007-03-21 |url-status=live |archive-url=https://web.archive.org/web/20070320064349/http://news.bbc.co.uk/2/hi/science/nature/4555235.stm |archive-date=20 March 2007}}</ref><ref>{{cite web |url=http://elements.vanderkrogt.net/element.php?sym=C |title=Carbonium/Carbon at Elementymology & Elements Multidict |author=van der Krogt, Peter |access-date=2010-01-06 |url-status=live |archive-url=https://web.archive.org/web/20100123003310/http://elements.vanderkrogt.net/element.php?sym=C |archive-date=2010-01-23}}</ref>

[[File:Carl Wilhelm Scheele from Familj-Journalen1874.png|thumb|upright|[[Carl Wilhelm Scheele]]]] In 1722, [[René Antoine Ferchault de Réaumur]] demonstrated that iron was transformed into steel through the absorption of some substance, now known to be carbon.<ref>{{cite book |last=Ferchault de Réaumur |first=R.-A. |date=1722 |title=L'art de convertir le fer forgé en acier, et l'art d'adoucir le fer fondu, ou de faire des ouvrages de fer fondu aussi finis que le fer forgé (English translation from 1956) |location=Paris, Chicago}}</ref> In 1772, [[Antoine Lavoisier]] showed that diamonds are a form of carbon; when he burned samples of charcoal and diamond and found that neither produced any water and that both released the same amount of carbon dioxide per gram. In 1779,<ref>{{cite web |url=http://www.canadaconnects.ca/chemistry/1009 |title=Carbon |publisher=Canada Connects |access-date=2010-12-07 |url-status=dead |archive-url=https://web.archive.org/web/20101027222156/http://canadaconnects.ca/chemistry/1009/ |archive-date=2010-10-27}}</ref> [[Carl Wilhelm Scheele]] showed that graphite, which had been thought of as a form of lead, was instead identical with charcoal but with a small admixture of iron, and that it gave "aerial acid" (his name for carbon dioxide) when oxidized with nitric acid.<ref name="Senese, Fred-2000">{{cite web |author=Senese, Fred |date=2000-09-09 |url=http://antoine.frostburg.edu/chem/senese/101/inorganic/faq/discovery-of-carbon.shtml |title=Who discovered carbon? |publisher=Frostburg State University |access-date=2007-11-24 |url-status=live |archive-url=https://web.archive.org/web/20071207230348/http://antoine.frostburg.edu/chem/senese/101/inorganic/faq/discovery-of-carbon.shtml |archive-date=2007-12-07}}</ref> In 1786, the French scientists [[Claude Louis Berthollet]], [[Gaspard Monge]] and C. A. Vandermonde confirmed that graphite was mostly carbon by oxidizing it in oxygen in much the same way Lavoisier had done with diamond.<ref>{{cite book |author=Giolitti, Federico |date=1914 |title=The Cementation of Iron and Steel |url=https://archive.org/details/cementationiron01rouigoog |publisher=McGraw-Hill Book Company, inc}}</ref> Some iron again was left, which the French scientists thought was necessary to the graphite structure. In their publication they proposed the name ''carbone'' (Latin ''carbonum'') for the element in graphite which was given off as a gas upon burning graphite. Antoine Lavoisier then listed carbon as an element in his 1789 textbook.<ref name="Senese, Fred-2000"/>

A new [[allotrope]] of carbon, [[fullerene]], that was discovered in 1985<ref>{{cite journal |journal=Nature |volume=318 |pages=162–163 |date=1985 |issue=6042 |bibcode=1985Natur.318..162K |doi=10.1038/318162a0 |s2cid=4314237 |title=C{{sub |60}}: Buckminsterfullerene |last1=Kroto|first1=H. W.|last2=Heath|first2=J. R.|last3=O'Brien|first3=S. C.|last4=Curl|first4=R. F.|last5=Smalley|first5=R. E.}}</ref> includes [[nanostructure]]d forms such as [[buckyball]]s and [[nanotubes]].<ref name="Unwin-2007">{{cite web |url=http://www.ch.ic.ac.uk/local/projects/unwin/Fullerenes.html |access-date=2007-12-08 |url-status=live |title=Fullerenes(An Overview) |author=Unwin, Peter |archive-url=https://web.archive.org/web/20071201165240/http://www.ch.ic.ac.uk/local/projects/unwin/Fullerenes.html |archive-date=2007-12-01}}</ref> Their discoverers&nbsp;– [[Robert Curl]], [[Harold Kroto]], and [[Richard Smalley]]&nbsp;– received the [[Nobel Prize]] in Chemistry in 1996.<ref>{{cite web |url=http://nobelprize.org/nobel_prizes/chemistry/laureates/1996/index.html |access-date=2007-12-21 |url-status=live |title=The Nobel Prize in Chemistry 1996 "for their discovery of fullerenes" |archive-url=https://web.archive.org/web/20071011035122/http://nobelprize.org/nobel_prizes/chemistry/laureates/1996/index.html |archive-date=2007-10-11}}</ref> The resulting renewed interest in new forms led to the discovery of further exotic allotropes, including [[glassy carbon]], and the realization that "[[amorphous carbon]]" is not strictly [[amorphous]].<ref name="Harris-2004">{{cite journal |url=http://www.physics.usyd.edu.au/~powles/PDFs/Harris_2004.pdf |url-status=dead |access-date=2011-07-06 |title=Fullerene-related structure of commercial glassy carbons |author=Harris, PJF |date=2004 |journal=Philosophical Magazine |volume=84 |pages=3159–3167 |doi=10.1080/14786430410001720363 |issue=29 |bibcode=2004PMag...84.3159H |citeseerx=10.1.1.359.5715 |s2cid=220342075 |archive-url=https://web.archive.org/web/20120319054641/http://www.physics.usyd.edu.au/~powles/PDFs/Harris_2004.pdf |archive-date=2012-03-19}}</ref>

==Production==

===Graphite===
{{Main|Graphite}}
Commercially viable natural deposits of graphite occur in many parts of the world, but the most important sources economically are in China, India, Brazil, and North Korea.<ref name="Simandl-2015">{{cite web | last1=Simandl | first1=George J. | last2=Akam | first2=Carlee | last3=Paradis | first3=Suzanne | title=Graphite deposit types, their origin, and economic significance | via=ResearchGate | date=2015-01-01 | url=https://www.researchgate.net/publication/288833915 | access-date=2024-11-07}}</ref> Graphite deposits are of [[metamorphic]] origin, found in association with [[quartz]], [[mica]], and [[feldspar]]s in schists, [[gneiss]]es, and metamorphosed [[sandstone]]s and [[limestone]] as [[lens (geology)|lenses]] or [[vein (geology)|veins]], sometimes of a metre or more in thickness. Deposits of graphite in [[Borrowdale]], [[Cumberland]], England were at first of sufficient size and purity that, until the 19th century, pencils were made by sawing blocks of natural graphite into strips before encasing the strips in wood. Today, smaller deposits of graphite are obtained by crushing the parent rock and floating the lighter graphite out on water.<ref name="USGS Minerals Yearbook">[http://minerals.usgs.gov/minerals/pubs/commodity/graphite USGS Minerals Yearbook: Graphite, 2009] {{webarchive|url=https://web.archive.org/web/20080916114706/http://minerals.usgs.gov/minerals/pubs/commodity/graphite/|date=2008-09-16}} and Graphite: Mineral Commodity Summaries 2011</ref>

There are three types of natural graphite—amorphous, flake or crystalline flake, and vein or lump. Amorphous graphite is the lowest quality and most abundant. Contrary to science, in industry "amorphous" refers to very small crystal size rather than complete lack of crystal structure. Amorphous is used for lower value graphite products and is the lowest priced graphite. Large amorphous graphite deposits are found in China, Europe, Mexico and the United States. Flake graphite is less common and of higher quality than amorphous; it occurs as separate plates that crystallized in metamorphic rock. Flake graphite can be four times the price of amorphous. Good quality flakes can be processed into [[expandable graphite]] for many uses, such as [[flame retardant]]s. The foremost deposits are found in Austria, Brazil, Canada, China, Germany and Madagascar. Vein or lump graphite is the rarest, most valuable, and highest quality type of natural graphite. It occurs in veins along intrusive contacts in solid lumps, and it is only commercially mined in Sri Lanka.<ref name="USGS Minerals Yearbook"/>

According to the [[USGS]], world production of natural graphite was 1.1&nbsp;million tonnes in 2010, to which China contributed 800,000&nbsp;t, India 130,000 t, Brazil 76,000&nbsp;t, North Korea 30,000&nbsp;t and Canada 25,000 t. No natural graphite was reported mined in the United States, but 118,000 t of synthetic graphite with an estimated value of $998&nbsp;million was produced in 2009.<ref name="USGS Minerals Yearbook"/>
{{Clear}}

===Diamond===
{{Main|Diamond}}
[[File:Global Diamond Output in 2005.png|thumb|upright=2.0|Diamond output in 2005]]
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 (see figure).

Only a very small fraction of the diamond ore consists of actual diamonds. The ore is crushed, during which care has to be taken in order to prevent larger diamonds from being destroyed in this process and subsequently the particles are 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, the separation was done with grease belts; diamonds have a stronger tendency to stick to grease than the other minerals in the ore.<ref>{{cite book |page=223 |title=The nature of diamonds |author=Harlow, G. E. |publisher=Cambridge University Press |date=1998 |isbn=978-0-521-62935-5}}</ref>

Historically diamonds were known to be found only in alluvial deposits in southern India.<ref name="Catelle-1911">{{cite book |last=Catelle |first=W. R. |title=The Diamond |publisher=John Lane Company |date=1911 |page=159}} discussion on alluvial diamonds in India and elsewhere as well as earliest finds</ref> India led the world in diamond production from the time of their discovery in approximately the 9th century BC<ref name="Ball-1881">{{cite book |last=Ball |first=V. |title=Diamonds, Gold and Coal of India |url=https://archive.org/details/diamondscoalgold00ballrich |publisher=London, Truebner & Co. |date=1881}} Ball was a Geologist in British service. Chapter I, Page 1</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>{{cite book |page=28 |title=The Book Of Diamonds: Their Curious Lore, Properties, Tests And Synthetic Manufacture |first=J. W. |last=Hershey |publisher=Kessinger Pub Co. |isbn=978-1-4179-7715-4 |date=1940}}</ref>

Diamond production of primary deposits (kimberlites and lamproites) only started in the 1870s after the discovery of the diamond fields in South Africa. Production has increased over time and an accumulated total of over 4.5&nbsp;billion carats have been mined since that date.<ref name="Janse-2007">{{cite journal |last=Janse |first=A. J. A. |title=Global Rough Diamond Production Since 1870 |journal=Gems and Gemology |volume=XLIII |issue=Summer 2007 |pages=98–119 |date=2007 |doi=10.5741/GEMS.43.2.98|bibcode=2007GemG...43...98J }}</ref> Most commercially viable diamond deposits were in Russia, Botswana, Australia and the Democratic Republic of Congo.<ref>{{cite web |url=http://gnn.tv/videos/2/The_Diamond_Life |title=The Diamond Life |publisher=Guerrilla News Network |first1=Stephen |last1=Marshall |last2=Shore |first2=Josh |access-date=2008-10-10 |date=2004-10-22 |archive-url=https://web.archive.org/web/20080609101643/http://gnn.tv/videos/2/The_Diamond_Life |archive-date=2008-06-09}}</ref> By 2005, Russia produced almost one-fifth of the global diamond output (mostly in [[Sakha Republic|Yakutia territory]]; for example, [[Mir Mine|Mir pipe]] and [[Udachnaya pipe]]) but the [[Argyle mine]] in Australia became the single largest source, producing 14 million carats in 2018.<ref>{{cite web |last1=Zimnisky |first1=Paul |date=21 May 2018 |title=Global Diamond Supply Expected to Decrease 3.4% to 147M Carats in 2018 |url=https://www.kitco.com/commentaries/2018-03-05/Global-Diamond-Supply-Expected-to-Decrease-3-4-to-147M-Carats-in-2018.html |access-date=9 November 2020 |website=Kitco.com |archive-date=11 August 2023 |archive-url=https://web.archive.org/web/20230811162409/https://www.kitco.com/commentaries/2018-03-05/Global-Diamond-Supply-Expected-to-Decrease-3-4-to-147M-Carats-in-2018.html |url-status=dead }}</ref><ref name="Lorenz-2007">{{cite journal |last=Lorenz |first=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 |date=2007}}</ref> New finds, the Canadian mines at [[Diavik Diamond Mine|Diavik]] and [[Ekati]], are expected to become even more valuable owing to their production of gem quality stones.<ref>Mannion pp. 25–26</ref>

In the United States, diamonds have been found in Arkansas, Colorado, and Montana.<ref>{{cite news |url=http://www.montanastandard.com/articles/2004/10/18/featuresbusiness/hjjfijicjbhdjc.txt |url-status=dead |title=Microscopic diamond found in Montana |newspaper=The Montana Standard |date=2004-10-17 |access-date=2008-10-10 |archive-url=https://web.archive.org/web/20050121085707/http://www.montanastandard.com/articles/2004/10/18/featuresbusiness/hjjfijicjbhdjc.txt |archive-date=2005-01-21}}</ref> In 2004, a startling discovery of a microscopic diamond in the United States<ref>{{cite web |url=http://www.livescience.com/environment/wyoming_diamond_041019.html |publisher=Livescience.com |access-date=2008-09-12 |title=Microscopic Diamond Found in Montana |first=Sarah |last=Cooke |date=2004-10-19 |archive-url=https://web.archive.org/web/20080705160039/http://www.livescience.com/environment/wyoming_diamond_041019.html |archive-date=2008-07-05}}</ref> led to the January 2008 bulk-sampling of [[kimberlite pipes]] in a remote part of Montana.<ref>{{cite web |url=http://www.deltamine.com/release2008-01-08.htm |title=Delta News / Press Releases / Publications |publisher=Deltamine.com |access-date=2008-09-12 |archive-url=https://web.archive.org/web/20080526154238/http://www.deltamine.com/release2008-01-08.htm |archive-date=2008-05-26}}</ref>

==Applications==
{{More citations needed section|date=April 2025}}
{{Gallery
|title=Applications of carbon
|width=110| height=130|noborder=yes
|align=center
|footer=
|File:Mechanical pencil lead spilling out 051907.jpg
 |Pencil leads for mechanical pencils are made of [[graphite]]
 |alt1=
|File:Charcoal sticks 051907.jpg
 |Sticks of vine and compressed [[charcoal]]
 |alt2=
|File:Kohlenstofffasermatte.jpg 
 |A cloth of woven carbon fibres
 |class3=
 |alt3=
|File:SiC p1390066.jpg
 |[[Silicon carbide]] [[single crystal]]
 |class4=
 |alt4=
|File:C60-Fulleren-kristallin.JPG
 |The ''C''{{sub|60}} fullerene in crystalline form
 |class5=
 |alt5=
|File:Tungsten carbide.jpg
 |[[Tungsten carbide]] [[endmills]]
 |class6=
 |alt6=
}}

Carbon is essential to all known living systems, and without it life as we know it could not exist (see [[alternative biochemistry]]). The major economic use of carbon other than food and wood is in the form of hydrocarbons, most notably the fossil fuel methane gas and crude oil (petroleum). Crude oil is distilled in refineries by the [[petrochemical industry]] to produce gasoline, kerosene, and other products. [[Cellulose]] is a natural, carbon-containing polymer produced by plants in the form of wood, cotton, linen, and [[hemp]]. Cellulose is used primarily for maintaining structure in plants. Commercially valuable carbon polymers of animal origin include wool, cashmere, and silk. Plastics are made from synthetic carbon polymers, often with oxygen and nitrogen atoms included at regular intervals in the main polymer chain. The raw materials for many of these synthetic substances come from crude oil.

The uses of carbon and its compounds are extremely varied. It can form [[alloy]]s with iron, of which the most common is [[carbon steel]]. Graphite is combined with clays to form the 'lead' used in pencils used for writing and drawing. It is also used as a lubricant and a pigment, as a moulding material in glass manufacture, in [[electrode]]s for dry batteries and in [[electroplating]] and [[electroforming]], in [[brush (electric)|brushes]] for [[electric motors]], and as a [[neutron moderator]] in [[nuclear reactor]]s.

Charcoal is used as a drawing material in artwork, barbecue grilling, [[iron smelting]], and in many other applications. Wood, coal and oil are used as fuel for production of energy and heating. Gem quality diamond is used in jewelry, and [[industrial diamond]]s are used in drilling, cutting and polishing tools for machining metals and stone. Plastics are made from fossil hydrocarbons, and [[carbon fiber]], made by [[pyrolysis]] of synthetic polyester fibers is used to reinforce plastics to form advanced, lightweight composite materials.

Carbon fiber is made by pyrolysis of extruded and stretched filaments of [[polyacrylonitrile]] (PAN) and other organic substances. The crystallographic structure and mechanical properties of the fiber depend on the type of starting material, and on the subsequent processing. Carbon fibers made from PAN have structure resembling narrow filaments of graphite, but thermal processing may re-order the structure into a continuous rolled sheet. The result is fibers with higher [[specific strength|specific tensile strength]] than steel.<ref name="Cantwell-1991">{{cite journal |first1=W. J. |last1=Cantwell |first2=J. |last2=Morton |title=The impact resistance of composite materials&nbsp;– a review |journal=Composites |date=1991 |volume=22 |issue=5 |pages=347–62 |doi=10.1016/0010-4361(91)90549-V}}</ref>

[[Carbon black]] is used as the black pigment in printing ink, artist's oil paint, and water colours, [[carbon paper]], automotive finishes, [[India ink]] and [[laser printer]] toner. Carbon black is also used as a filler in rubber products such as tyres and in plastic compounds. [[Activated charcoal]] is used as an [[absorption (chemistry)|absorbent]] and [[adsorbent]] in [[filter (chemistry)|filter]] material in applications as diverse as gas masks, water purification, and kitchen [[extractor hood]]s, and in medicine to absorb toxins, poisons, or gases from the digestive system. Carbon is used in [[chemical reduction]] at high temperatures. [[Coke (fuel)|Coke]] is used to reduce iron ore into iron (smelting). [[Case hardening]] of steel is achieved by heating finished steel components in carbon powder. [[Carbide]]s of [[silicon carbide|silicon]], [[tungsten carbide|tungsten]], [[boron carbide|boron]], and [[titanium carbide|titanium]] are among the hardest known materials, and are used as abrasives in cutting and grinding tools. Carbon compounds make up most of the materials used in clothing, such as natural and synthetic textiles and leather, and almost all of the interior surfaces in the built environment other than glass, stone, drywall, and metal.
{{Clear}}

===Diamonds===
The [[diamond]] industry falls into two categories: one dealing with gem-grade diamonds and the other, with industrial-grade diamonds. While a large trade in both types of diamonds exists, the two markets function dramatically differently.

Unlike [[precious metal]]s such as gold or platinum, gem diamonds do not trade as a commodity. There is a substantial mark-up in the sale of diamonds, and there is not a very active market for resale of diamonds.

Industrial diamonds are valued mostly for their hardness and heat conductivity, with the gemological qualities of clarity and color being mostly irrelevant. About 80% of mined diamonds (equal to about 100 million carats or 20&nbsp;tonnes annually) are unsuitable for use as gemstones and relegated for industrial use (known as ''[[bort]])''.<ref>{{cite book |title=Turning And Mechanical Manipulation |first=Ch. |last=Holtzapffel |publisher=Charles Holtzapffel |date=1856 |url=https://archive.org/details/turningandmecha01holtgoog}} [https://archive.org/details/turningmechanica02holtuoft Internet Archive] {{webarchive|url=https://web.archive.org/web/20160326085110/https://archive.org/details/turningmechanica02holtuoft|date=2016-03-26}}</ref> [[Synthetic diamond]]s, invented in the 1950s, found almost immediate industrial applications; 3&nbsp;billion carats (600&nbsp;[[tonne]]s) of synthetic diamond is produced annually.<ref name="USGS-2009">{{cite web |url=http://minerals.usgs.gov/minerals/pubs/commodity/diamond/ |access-date=2009-05-05 |title=Industrial Diamonds Statistics and Information |publisher=United States Geological Survey |url-status=live |archive-url=https://web.archive.org/web/20090506221551/http://minerals.usgs.gov/minerals/pubs/commodity/diamond/ |archive-date=2009-05-06}}</ref>

The dominant industrial use of diamond is in cutting, drilling, grinding, and polishing. Most of these applications do not require large diamonds; in fact, most diamonds of gem-quality except for their small size can be used industrially. Diamonds are embedded in drill tips or saw blades, or ground into a powder for use in grinding and polishing applications.<ref>{{cite journal |first1=R. T. |last1=Coelho |title=The application of polycrystalline diamond (PCD) tool materials when drilling and reaming aluminum-based alloys including MMC |doi=10.1016/0890-6955(95)93044-7 |journal=International Journal of Machine Tools and Manufacture |volume=35 |date=1995 |pages=761–774 |issue=5 |last2=Yamada |first2=S. |last3=Aspinwall |first3=D. K. |last4=Wise |first4=M. L. H.}}</ref> Specialized applications include use in laboratories as containment for [[high-pressure experiments]] (see [[diamond anvil cell]]), high-performance [[bearing (mechanical)|bearings]], and limited use in specialized windows.<ref>{{cite book |pages=303–334 |title=Materials for infrared windows and domes: properties and performance |first=D. C. |last=Harris |publisher=SPIE Press |date=1999 |isbn=978-0-8194-3482-1}}</ref><ref>{{cite book |first=G. S. |last=Nusinovich |title=Introduction to the physics of gyrotrons |publisher=JHU Press |date=2004 |isbn=978-0-8018-7921-0 |page=229}}</ref> With the continuing advances in the production of synthetic diamonds, new applications are becoming feasible. Garnering much excitement is the possible use of diamond as a [[semiconductor]] suitable for [[microchips]], and because of its exceptional heat conductance property, as a [[heat sink]] in electronics.<ref>{{cite journal |title=120 W CW output power from monolithic AlGaAs (800 nm) laser diode array mounted on diamond heatsink |first1=M. |last1=Sakamoto |first2=J. G. |last2=Endriz |first3=D. R. |last3=Scifres |journal=Electronics Letters |date=1992 |volume=28 |issue=2 |pages=197–199 |doi=10.1049/el:19920123 |bibcode=1992ElL....28..197S}}</ref>

==Precautions==
[[File:Worker at carbon black plant2.jpg|thumb|left|upright|Worker at [[carbon black]] plant in [[Sunray, Texas]] (photo by [[John Vachon]], 1942)]]
[[File:Centrilobular emphysema 865 lores.jpg|thumb|upright=1.3|Gross pathology of lung showing centrilobular emphysema characteristic of smoking. Closeup of fixed, cut surface shows multiple cavities lined by heavy black carbon deposits.]]

Pure carbon has extremely low toxicity to humans and can be handled safely in the form of graphite or charcoal. It is resistant to dissolution or chemical attack, even in the acidic contents of the digestive tract. Consequently, once it enters into the body's tissues it is likely to remain there indefinitely. Carbon black was probably one of the first pigments to be used for tattooing, and [[Ötzi the Iceman]] was found to have carbon tattoos that survived during his life and for 5200&nbsp;years after his death.<ref>{{cite journal |first1=Leopold |last1=Dorfer |date=1998 |title=5200-year old acupuncture in Central Europe? |journal=Science |volume=282 |pages=242–243 |doi=10.1126/science.282.5387.239f |pmid=9841386 |last2=Moser |first2=M. |last3=Spindler |first3=K. |last4=Bahr |first4=F. |last5=Egarter-Vigl |first5=E. |last6=Dohr |first6=G. |issue=5387 |bibcode=1998Sci...282..239D |s2cid=42284618}}</ref> Inhalation of coal dust or soot (carbon black) in large quantities can be dangerous, irritating lung tissues and causing the congestive lung disease, [[coalworker's pneumoconiosis]]. Diamond dust used as an abrasive can be harmful if ingested or inhaled. Microparticles of carbon are produced in diesel engine exhaust fumes, and may accumulate in the lungs.<ref>{{cite journal |last1=Donaldson |first1=K. |date=2001 |title=Ultrafine particles |journal=Occupational and Environmental Medicine |volume=58 |pages=211–216 |doi=10.1136/oem.58.3.211 |pmid=11171936 |last2=Stone |first2=V. |last3=Clouter |first3=A. |last4=Renwick |first4=L. |last5=MacNee |first5=W. |issue=3 |pmc=1740105}}</ref> In these examples, the harm may result from contaminants (e.g., organic chemicals, heavy metals) rather than from the carbon itself.

Carbon generally has low toxicity to life on Earth; but carbon nanoparticles are deadly to ''[[Drosophila]]''.<ref>[https://www.sciencedaily.com/releases/2009/08/090807103921.htm Carbon Nanoparticles Toxic To Adult Fruit Flies But Benign To Young] {{webarchive|url=https://web.archive.org/web/20111102130334/https://www.sciencedaily.com/releases/2009/08/090807103921.htm |date=2011-11-02}} ScienceDaily (Aug. 17, 2009)</ref>

Carbon may burn vigorously and brightly in the presence of air at high temperatures. Large accumulations of coal, which have remained inert for hundreds of millions of years in the absence of oxygen, may [[spontaneously combust]] when exposed to air in coal mine waste tips, ship cargo holds and coal bunkers,<ref>{{cite web |url=https://www.geosociety.org/news/pr/04-30.htm |title=Press Release – Titanic Disaster: New Theory Fingers Coal Fire |website=www.geosociety.org |access-date=2016-04-06 |url-status=live |archive-url=https://web.archive.org/web/20160414183351/http://geosociety.org/news/pr/04-30.htm |archive-date=2016-04-14}}</ref><ref>{{cite web |url=http://www.spanamwar.com/mainecoal.html |title=Coal bunker Fire |last=McSherry |first=Patrick |website=www.spanamwar.com |access-date=2016-04-06 |url-status=live |archive-url=https://web.archive.org/web/20160323134109/http://www.spanamwar.com/mainecoal.html |archive-date=2016-03-23}}</ref> and storage dumps.

In nuclear applications where graphite is used as a [[neutron moderator]], accumulation of [[Wigner energy]] followed by a sudden, spontaneous release may occur. [[Annealing (metallurgy)|Annealing]] to at least 250&nbsp;°C can release the energy safely, although in the [[Windscale fire]] the procedure went wrong, causing other reactor materials to combust.

The great variety of carbon compounds include such lethal poisons as [[tetrodotoxin]], the [[lectin]] [[ricin]] from seeds of the [[castor oil plant]] ''[[Ricinus communis]]'', [[cyanide]] (CN{{sup|−}}), and carbon monoxide; and such essentials to life as glucose and protein.

==See also==
{{Div col |small=yes |colwidth=30em}}
* [[Carbon chauvinism]]
* [[Carbon detonation]]
* [[Carbon footprint]]
* [[Carbon star]]
* [[Carbon planet]]
* [[Low-carbon economy]]
* [[Timeline of carbon nanotubes]]
{{Div col end}}

==References==
{{Reflist|30em}}

==Bibliography==
* {{Greenwood&Earnshaw2nd}}
* {{cite book |isbn=978-1-4020-3956-0 |title=Carbon and Its Domestication |last1=Mannion |first1=A. M. |date=12 January 2006 |publisher=[[Springer Science+Business Media|Springer]] |pages=1–319}}

==External links==
* {{In Our Time|Carbon|p003c1cj|Carbon}}
* [http://www.periodicvideos.com/videos/006.htm Carbon] at ''[[The Periodic Table of Videos]]'' (University of Nottingham)
* [https://www.britannica.com/eb/article-80956/carbon-group-element Carbon on Britannica]
* [https://web.archive.org/web/20100618165649/http://invsee.asu.edu/nmodules/Carbonmod/everywhere.html Extensive Carbon page at asu.edu] (archived 18 June 2010)
* [https://web.archive.org/web/20011109080742/http://electrochem.cwru.edu/ed/encycl/art-c01-carbon.htm Electrochemical uses of carbon] (archived 9 November 2001)
* [https://web.archive.org/web/20121109012854/http://www.forskning.no/Artikler/2006/juni/1149432180.36 Carbon—Super Stuff. Animation with sound and interactive 3D-models.] (archived 9 November 2012)

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{{Allotropes of carbon}}
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[[Category:Carbon| ]]
[[Category:Allotropes of carbon]]
[[Category:Chemical elements with hexagonal planar structure]]
[[Category:Chemical elements]]
[[Category:Native element minerals]]
[[Category:Polyatomic nonmetals]]
[[Category:Reactive nonmetals]]
[[Category:Reducing agents]]