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{{Infobox osmium}}

'''Osmium''' ({{etymology|grc|''{{wikt-lang|grc|ὀσμή}}'' ({{grc-transl|ὀσμή}})|smell}}) is a [[chemical element]]; it has [[Symbol (chemistry)|symbol]] '''Os''' and [[atomic number]] 76. It is a hard, brittle, bluish-white [[transition metal]] in the [[platinum group]] that is found as a [[Abundance of elements in Earth's crust|trace element]] in alloys, mostly in [[platinum]] ores. Osmium has the highest [[density]] of any stable element ({{val|22.59|u=g/cm3}}).<ref name="Arblaster1995"/> It is also one of the [[Abundance of elements in Earth's crust|rarest elements]] in the Earth's crust, with an estimated abundance of 50 parts per trillion ([[Parts-per notation#Parts-per expressions|ppt]]).<ref>{{Cite web|url=https://pubs.usgs.gov/circ/1953/0285/report.pdf|title=Recent estimates of the abundances of the elements in the Earth's crust|last=Fleischer|first=Michael|date=1953|publisher=U.S. Geological Survey|access-date=May 10, 2018|archive-date=October 23, 2022|archive-url=https://web.archive.org/web/20221023210114/https://pubs.usgs.gov/circ/1953/0285/report.pdf|url-status=live}}</ref><ref>{{Cite web|url=https://courses.lumenlearning.com/geology/chapter/reading-abundance-of-elements-in-earths-crust/|title=Reading: Abundance of Elements in Earth's Crust {{!}} Geology|website=courses.lumenlearning.com|access-date=2018-05-10|archive-date=May 17, 2022|archive-url=https://web.archive.org/web/20220517201915/https://courses.lumenlearning.com/geology/chapter/reading-abundance-of-elements-in-earths-crust/|url-status=live}}</ref> Manufacturers use [[alloy]]s of osmium with platinum, [[iridium]], and other platinum-group metals for [[fountain pen]] [[Nib (pen)#Nib tipping|nib tipping]], [[electrical contacts]], and other applications that require extreme durability and [[hardness]].{{sfn|Haynes|2011|p=4.25}} 

== Characteristics ==
=== Physical properties ===
[[File:Osmium 1-crop.jpg|thumb|left|upright|Osmium, remelted pellet]]

Osmium is a hard, brittle, blue-gray metal, and the densest [[stable element]]—about twice as dense as [[lead]]. The density of osmium is slightly greater than that of [[iridium]]; the two are so similar (22.587  versus {{val|22.562|ul=g/cm3}} at 20&nbsp;°C) that each was at one time considered to be the densest element. Only in the 1990s were measurements made accurately enough (by means of [[X-ray crystallography]]) to be certain that osmium is the denser of the two.<ref name="Arblaster1995">{{cite journal|title=Osmium, the Densest Metal Known|author=Arblaster, J. W.|journal=[[Platinum Metals Review]]|volume=39|issue=4|year=1995|page=164|doi=10.1595/003214095X394164164 |url=https://technology.matthey.com/article/39/4/164-164/|access-date=November 11, 2023|archive-url=https://web.archive.org/web/20230506024553/https://technology.matthey.com/article/39/4/164-164|archive-date=May 6, 2023|url-status=live|url-access=subscription}}</ref><ref>{{cite journal |last1=Girolami |first1=Gregory |title=Osmium weighs in |journal=Nature Chemistry |date=November 2012 |volume=4 |issue=11 |page=954 |doi=10.1038/nchem.1479|doi-access=free |pmid=23089872 |bibcode=2012NatCh...4..954G }}</ref>

Osmium has a blue-gray tint.{{sfn|Haynes|2011|p=4.25}} The [[reflectivity]] of single crystals of osmium is complex and strongly direction-dependent, with light in the red and near-infrared wavelengths being more strongly absorbed when [[polarization (waves)|polarized]] parallel to the ''c'' crystal axis than when polarized perpendicular to the ''c'' axis; the ''c''-parallel polarization is also slightly more reflected in the mid-ultraviolet range. Reflectivity reaches a sharp minimum at around 1.5&nbsp;eV (near-infrared) for the ''c''-parallel polarization and at 2.0&nbsp;eV (orange) for the ''c''-perpendicular polarization, and peaks for both in the visible spectrum at around 3.0&nbsp;eV (blue-violet).<ref>{{cite journal |last1=Nemoshkalenko |first1=V. V. |last2=Antonov |first2=V. N. |last3=Kirillova |first3=M. M. |last4=Krasovskii |first4=A. E. |last5=Nomerovannaya |first5=L. V. |title=The structure of the energy bands and optical absorption in osmium |journal=Sov. Phys. JETP |date=January 1986 |volume=63 |issue=I |page=115 |bibcode=1986JETP...63..115N |url=http://www.jetp.ras.ru/cgi-bin/dn/e_063_01_0115.pdf |access-date=28 December 2022 |archive-date=March 11, 2023 |archive-url=https://web.archive.org/web/20230311062236/http://www.jetp.ras.ru/cgi-bin/dn/e_063_01_0115.pdf |url-status=live }}</ref>

Osmium is a hard but brittle [[metal]] that remains [[lustrous]] even at high temperatures. It has a very low [[compressibility]]. Correspondingly, its [[bulk modulus]] is extremely high, reported between {{val|395}} and {{val|462|ul=GPa}}, which rivals that of [[diamond]] ({{val|443|u=GPa}}). The hardness of osmium is moderately high at {{val|4|u=GPa}}.<ref>{{cite journal|title=Osmium Metal Studied under High Pressure and Nonhydrostatic Stress|journal=Phys. Rev. Lett.|volume=100|issue=4|article-number=045506|date=2008|doi=10.1103/PhysRevLett.100.045506|pmid=18352299|bibcode=2008PhRvL.100d5506W|last1=Weinberger|first1=Michelle|last2=Tolbert|first2=Sarah|last3=Kavner|first3=Abby|s2cid=29146762}}</ref><ref>{{cite journal|first=Hyunchae|last=Cynn|author2=Klepeis, J. E.|author3=Yeo, C. S.|author4=Young, D. A.|title=Osmium has the Lowest Experimentally Determined Compressibility|journal=Physical Review Letters|volume=88|issue=13|date=2002|doi=10.1103/PhysRevLett.88.135701|article-number=135701|pmid=11955108|bibcode=2002PhRvL..88m5701C|url=https://zenodo.org/record/1233939|access-date=August 27, 2019|archive-date=September 28, 2023|archive-url=https://web.archive.org/web/20230928093417/https://zenodo.org/record/1233939|url-status=live}}</ref><ref>{{cite journal|first=B. R.|last=Sahu|author2=Kleinman, L.|title=Osmium Is Not Harder Than Diamond|journal=Physical Review B|volume=72|date=2005|issue=11|doi=10.1103/PhysRevB.72.113106|article-number=113106|bibcode=2005PhRvB..72k3106S }}</ref> Because of its [[hardness]], brittleness, low [[vapor pressure]] (the lowest of the platinum-group metals), and very high [[melting point]] (the [[List of elements by melting point|fourth highest]] of all elements, after [[carbon]], [[tungsten]], and [[rhenium]]), solid osmium is difficult to machine, form, or work.

=== Chemical properties ===
{{Main article|Osmium compounds}}
<div style="float:right; margin:5px;">
{|class="wikitable"
|-
! colspan=2|Oxidation states of osmium
|-
| −4 || [OsIn<sub>6−''x''</sub>Sn<sub>''x''</sub>]<ref name="MetalAnions">Fe(−4), Ru(−4), and Os(−4) have been observed in metal-rich compounds containing octahedral complexes [MIn<sub>6−''x''</sub>Sn<sub>''x''</sub>]; Pt(−3) (as a dimeric anion [Pt–Pt]<sup>6−</sup>), Cu(−2), Zn(−2), Ag(−2), Cd(−2), Au(−2), and Hg(−2) have been observed (as dimeric and monomeric anions; dimeric ions were initially reported to be [T–T]<sup>2−</sup> for Zn, Cd, Hg, but later shown to be [T–T]<sup>4−</sup> for all these elements) in La<sub>2</sub>Pt<sub>2</sub>In, La<sub>2</sub>Cu<sub>2</sub>In, Ca<sub>5</sub>Au<sub>3</sub>, Ca<sub>5</sub>Ag<sub>3</sub>, Ca<sub>5</sub>Hg<sub>3</sub>, Sr<sub>5</sub>Cd<sub>3</sub>, Ca<sub>5</sub>Zn<sub>3</sub>(structure (AE<sup>2+</sup>)<sub>5</sub>(T–T)<sup>4−</sup>T<sup>2−</sup>⋅4e<sup>−</sup>), Yb<sub>3</sub>Ag<sub>2</sub>, Ca<sub>5</sub>Au<sub>4</sub>, and Ca<sub>3</sub>Hg<sub>2</sub>; Au(–3) has been observed in ScAuSn and in other 18-electron half-Heusler compounds. See {{cite journal|title=Late transition metal anions acting as p-metal elements|year=2008|author1=Changhoon Lee|author2=Myung-Hwan Whangbo|volume=10|issue=4|pages=444–449|journal=Solid State Sciences|doi=10.1016/j.solidstatesciences.2007.12.001|bibcode=2008SSSci..10..444K}} and {{cite journal|doi=10.1002/zaac.200900421|title=Analysis of Electronic Structures and Chemical Bonding of Metal-rich Compounds. 2. Presence of Dimer (T–T)<sup>4–</sup> and Isolated T<sup>2–</sup> Anions in the Polar Intermetallic Cr<sub>5</sub>B<sub>3</sub>-Type Compounds AE<sub>5</sub>T<sub>3</sub> (AE = Ca, Sr; T = Au, Ag, Hg, Cd, Zn)|year=2010|author1=Changhoon Lee|author2=Myung-Hwan Whangbo|author3=Jürgen Köhler|volume=636|issue=1|pages=36–40|journal=Zeitschrift für Anorganische und Allgemeine Chemie}}</ref>
|-
| −2 || {{chem|Na|2|[Os(CO)|4|]}}
|-
| −1 || {{chem|Na|2|[Os|4|(CO)|13|]}}
|-
| 0 ||[[Triosmium dodecacarbonyl|{{chem|Os|3|(CO)|12|}}]]
|-
| +1 ||{{chem|OsI}}
|-
| '''+2''' ||{{chem|OsI|2}}
|-
| '''+3''' || {{chem| OsBr|3|}}
|-
| '''+4''' || [[Osmium dioxide|{{chem|OsO|2}}]], [[Osmium(IV) chloride|{{chem|OsCl|4}}]]
|-
| +5 ||{{chem|OsF|5}}
|-
| +6 ||[[Osmium hexafluoride|{{chem|OsF|6}}]]
|-
| +7 ||{{chem|OsOF|5}}
|-
| '''+8''' ||[[Osmium tetroxide|{{chem|OsO|4}}]], {{chem|Os|(|NCH|3|)|4}}
|}</div>

Osmium forms compounds with [[oxidation state]]s ranging from −4 to +8. The most common oxidation states are +2, +3, +4, and +8. The +8 oxidation state is notable for being the highest attained by any chemical element aside from iridium's +9<ref>{{cite web|url=http://www.rsc.org/chemistryworld/2014/10/iridium-oxide-cation-oxidation-state-9|title=Iridium forms compound in +9 oxidation state|author=Stoye, Emma|work=Chemistry World|date=23 October 2014|publisher=[[Royal Society of Chemistry]]|access-date=December 19, 2014|archive-date=August 9, 2016|archive-url=https://web.archive.org/web/20160809143724/http://www.rsc.org/chemistryworld/2014/10/iridium-oxide-cation-oxidation-state-9|url-status=live}}</ref> and is encountered only in [[xenon]],<ref name="selig">{{cite journal|title=Xenon tetroxide – Preparation + Some Properties|journal=Science| date=1964 |volume=143|pages=1322–1323| doi=10.1126/science.143.3612.1322|pmid=17799234|issue=3612|jstor=1713238|bibcode=1964Sci...143.1322S|last1=Selig|first1=H.|display-authors=4|last2=Claassen|first2=H. H.|last3=Chernick|first3=C. L.|last4=Malm|first4=J. G.|last5=Huston|first5=J. L.|s2cid=29205117}}</ref><ref>{{cite journal|title=Xenon tetroxide – Mass Spectrum|journal=Science|date=1964|volume=143|pages=1162–1163|doi=10.1126/science.143.3611.1161-a|pmid=17833897|issue=3611|jstor=1712675|bibcode=1964Sci...143.1161H|last1=Huston|first1=J. L.|last2=Studier|first2=M. H.|last3=Sloth|first3=E. N.|s2cid=28547895}}</ref> [[ruthenium]],<ref>{{cite journal|doi=10.1595/147106704X10801|title=Oxidation States of Ruthenium and Osmium|date=2004|author=Barnard, C. F. J.|journal=Platinum Metals Review|volume=48|issue=4|page=157|doi-access=free}}</ref> [[hassium]],<ref>{{cite web|url=http://www.gsi.de/documents/DOC-2003-Jun-29-2.pdf|archive-url=https://web.archive.org/web/20120114084650/http://www.gsi.de/documents/DOC-2003-Jun-29-2.pdf|archive-date=2012-01-14|title=Chemistry of Hassium|access-date=2007-01-31|date=2002|work=Gesellschaft für Schwerionenforschung mbH}}</ref> [[iridium]],<ref>{{cite journal|doi=10.1002/anie.200902733|pmid=19593837|title=Formation and Characterization of the Iridium Tetroxide Molecule with Iridium in the Oxidation State +VIII|date=2009|last1=Gong|first1=Yu|last2=Zhou|first2=Mingfei|last3=Kaupp|first3=Martin|last4=Riedel|first4=Sebastian|journal=Angewandte Chemie International Edition|volume=48|issue=42|pages=7879–7883 |bibcode=2009ACIE...48.7879G }}{{dead link|date=June 2019}}</ref> and [[plutonium]].<ref>{{cite journal |last1=Kiselev |first1=Yu. M. |last2=Nikonov |first2=M. V. |last3=Dolzhenko |first3=V. D. |last4=Ermilov |first4=A. Yu. |last5=Tananaev |first5=I. G. |last6=Myasoedov |first6=B. F. |title=On existence and properties of plutonium(VIII) derivatives |journal=Radiochimica Acta |date=17 January 2014 |volume=102 |issue=3 |pages=227–237 |doi=10.1515/ract-2014-2146|s2cid=100915090 }}</ref><ref>{{cite journal |last1=Zaitsevskii |first1=Andréi |last2=Mosyagin |first2=Nikolai S. |last3=Titov |first3=Anatoly V. |last4=Kiselev |first4=Yuri M. |title=Relativistic density functional theory modeling of plutonium and americium higher oxide molecules |journal=The Journal of Chemical Physics |date=21 July 2013 |volume=139 |issue=3 |page=034307 |doi=10.1063/1.4813284 |pmid=23883027 |bibcode=2013JChPh.139c4307Z }}</ref> Examples of the −1 and −2 oxidation states are {{chem|Na|2|[Os|4|(CO)|13|]}} and {{chem|Na|2|[Os(CO)|4|]}}, respectively; these reactive compounds are used to synthesize osmium [[Cluster chemistry#Transition metal carbonyl clusters|cluster compounds]].<ref>{{cite journal|doi=10.1016/0022-328X(93)83250-Y|title=Preparation of [Os<sub>3</sub>(CO)<sub>11</sub>]<sup>2−</sup> and its reactions with Os<sub>3</sub>(CO)<sub>12</sub>; structures of [Et<sub>4</sub>N] [HOs<sub>3</sub>(CO)<sub>11</sub>] and H<sub>2</sub>OsS<sub>4</sub>(CO)|date=1993|last1 =Krause|first1=J.|journal=Journal of Organometallic Chemistry|volume=454|issue=1–2|pages=263–271|display-authors=4|last2=Siriwardane|first2=Upali|last3=Salupo|first3=Terese A.|last4=Wermer|first4=Joseph R.|last5=Knoeppel|first5=David W.|last6=Shore|first6=Sheldon G.}}</ref><ref>{{cite journal|doi=10.1021/ic00141a019|title=Mononuclear hydrido alkyl carbonyl complexes of osmium and their polynuclear derivatives|date=1982|first=Willie J.|last=Carter|display-authors=4|author2=Kelland, John W. |author3=Okrasinski, Stanley J. |author4=Warner, Keith E. |author5= Norton, Jack R. | journal=Inorganic Chemistry|volume=21|issue=11|pages=3955–3960}}</ref>

[[File:Osmiumtetroxide1.jpg|thumb|left|Osmium tetroxide ({{chem2|OsO4}})]]

The most common compound exhibiting the +8 oxidation state, [[osmium tetroxide]] ({{chem2|OsO4}}), is a volatile, water-soluble solid with a "pronounced and nauseating" smell.<ref name="mager">{{cite book| last = Mager Stellman| first = J.| title = Encyclopaedia of Occupational Health and Safety| chapter-url = https://books.google.com/books?id=nDhpLa1rl44C| date = 1998| publisher = International Labour Organization| isbn = 978-92-2-109816-4| oclc = 35279504| pages = [https://archive.org/details/encyclopaediaofo0003unse/page/63 63.34]| chapter = Osmium| url = https://archive.org/details/encyclopaediaofo0003unse/page/63}}</ref> Osmium tetroxide forms red perosmates {{chem|OsO|4|(OH)|2|2-}} upon reaction with a base. With [[ammonia]], it forms the nitrido-osmates [[Potassium osmiamate|{{chem|OsO|3|N|-}}]].<ref name="Holle">{{cite book| author2 = Wiberg, E.| author3 = Wiberg, N.| last = Holleman| first = A. F.| title = Inorganic Chemistry| edition = 1st| date = 2001| publisher = Academic Press| isbn = 978-0-12-352651-9| oclc = 47901436 }}</ref><ref name="Griffith">{{cite journal|journal=Quarterly Reviews, Chemical Society|date=1965|volume=19|issue=3|pages=254–273|doi=10.1039/QR9651900254|title=Osmium and its compounds|first=W. P.|last=Griffith}}</ref><ref>{{cite book| author = ((Subcommittee on Platinum-Group Metals, Committee on Medical and Biologic Effects of Environmental Pollutants, Division of Medical Sciences, Assembly of Life Sciences, National Research Council)) | title = Platinum-group metals| url = https://books.google.com/books?id=yEcrAAAAYAAJ| date = 1977| publisher = National Academy of Sciences| isbn = 978-0-309-02640-6| page = 55 }}</ref> The +4 oxide, [[osmium dioxide]] ({{chem|Os|O|2}}), is a darkly-colored, non-volatile, and much less reactive compound.

Osmium pentafluoride ({{chem|Os|F|5}}) is known, but osmium trifluoride ({{chem|Os|F|3}}) has not yet been synthesized. The lower oxidation states are stabilized by the larger halogens, so that the trichloride, tribromide, triiodide, and even diiodide are known. The oxidation state +1 is known only for osmium monoiodide (OsI), whereas several carbonyl complexes of osmium, such as [[triosmium dodecacarbonyl]] ({{chem|Os|3|(CO)|12}}), represent oxidation state 0.<ref name="Holle" /><ref name="Griffith" /><ref name="greenwood">{{cite book |editor1-last=Greenwood |editor1-first=N.N. |editor2-last=Earnshaw |editor2-first=A. |title=Chemistry of the Elements |date=1997 |publisher=Butterworth-Heinemann |isbn=978-0-7506-3365-9 |pages=1070–1112 |edition=2 |chapter=25 - Iron, Ruthenium and Osmium|doi=10.1016/B978-0-7506-3365-9.50031-6 }}</ref><ref>{{cite journal|title=The chemistry of ruthenium, osmium, rhodium, iridium, palladium, and platinum in the higher oxidation states|journal=Coordination Chemistry Reviews|volume=46|date=1982|pages=1–127|author=Gulliver, D. J|author2=Levason, W.|doi=10.1016/0010-8545(82)85001-7}}</ref>

In general, the lower oxidation states of osmium are stabilized by [[ligand]]s that are good σ-donors (such as [[amines]]) and π-acceptors ([[heterocyclic compound|heterocycles]] containing [[nitrogen]]). The higher oxidation states are stabilized by strong σ- and π-donors, such as {{chem|O|2-}} and {{chem|N|3-}}.<ref>{{cite book| author = Sykes, A. G. | title = Advances in Inorganic Chemistry| url = https://archive.org/details/advancesinorgani39syke | url-access = limited | date = 1992| publisher = Academic Press| isbn = 978-0-12-023637-4| page = [https://archive.org/details/advancesinorgani39syke/page/n227 221]}}</ref>

Despite its broad range of compounds in numerous oxidation states, osmium in bulk form at ordinary temperatures and pressures is stable in air. It resists attack by most acids and bases including [[aqua regia]], but is attacked by {{chem2|F2}} and {{chem2|Cl2}} at high temperatures, and by hot concentrated nitric acid to produce {{chem2|OsO4}}. It can be dissolved by molten alkalis fused with an oxidizer such as [[sodium peroxide]] ({{chem2|Na2O2}}) or [[potassium chlorate]] ({{chem2|KClO3}}) to give osmates such as [[potassium osmate|{{chem2|K2[OsO2(OH)4]}}]].<ref name="greenwood" />

=== Isotopes ===
{{Main|Isotopes of osmium}}
Osmium has seven naturally occurring [[isotope]]s, five of which are stable: {{chem|187|Os}}, {{chem|188|Os}}, {{chem|189|Os}}, {{chem|190|Os}}, and (most abundant) {{chem|192|Os}}. At least 37 artificial radioisotopes and 20 [[nuclear isomer]]s exist, with mass numbers ranging from 160 to 203; the most stable of these is {{chem|194|Os}} with a half-life of 6.0 years.<ref name="nubase">{{NUBASE2020}}</ref>

The two primordial radioisotopes {{chem|184|Os}} and {{chem|186|Os}} are known to undergo [[alpha decay]] with long [[half-life|half-lives]]: the current best values being {{val|1.12e13|0.23}} and {{val|2.0e15|1.1}} years, approximately {{val|140000}} times the [[age of the universe]], that for practical purposes it can be considered stable. Alpha decay is predicted for all the other naturally occurring isotopes, but has not been observed, presumably due to very long half-lives; {{chem|184|Os}} and {{chem|192|Os}} are also predicted to undergo [[double beta decay]], but this not been observed either.<ref name="nubase"/>

<sup>189</sup>Os has a spin of 3/2{{r|"nubase"|page=131}} but <sup>187</sup>Os has a nuclear spin 1/2{{r|"nubase"|page=130}}. Its low natural abundance (1.64%) and low nuclear magnetic moment means that it is one of the most difficult natural abundance isotopes for [[NMR spectroscopy]].<ref>{{cite journal|doi=10.1021/om960053i |title=<sup>187</sup>Os NMR Study of (η<sup>6</sup>-Arene)osmium(II) Complexes: Separation of Electronic and Steric Ligand Effects |date=1996 |last1=Bell |first1=Andrew G. |last2=Koźmiński |first2=Wiktor |last3=Linden |first3=Anthony |last4=von Philipsborn |first4=Wolfgang |journal=Organometallics |volume=15 |issue=14 |pages=3124–3135 }}</ref>

{{chem|187|Os}} is the descendant of {{chem|187|[[rhenium|Re]]}} (half-life {{val|4.12|e=10|u=years}}) and is used extensively in dating terrestrial as well as [[meteorite|meteoric]] [[rock (geology)|rocks]] (see ''[[Rhenium–osmium dating]]''). It has also been used to measure the intensity of continental weathering over geologic time and to fix minimum ages for stabilization of the [[Earth's mantle|mantle]] roots of continental [[craton]]s. This decay is a reason why rhenium-rich minerals are abnormally rich in {{chem|187|Os}}.<ref>{{cite journal|first=Józef|last=Dąbek|author2=Halas, Stanislaw|title=Physical Foundations of Rhenium-Osmium Method – A Review|journal=Geochronometria|volume=27|date=2007|issue=1 |doi=10.2478/v10003-007-0011-4|pages=23–26|bibcode=2007Gchrm..27...23D |doi-access=free}}</ref>

== History ==
Osmium was discovered in 1803 by [[Smithson Tennant]] and [[William Hyde Wollaston]] in [[London]], England.<ref>{{cite journal|title=Osmium|journal=Metallurgist|volume=18|issue= 2|date=1974|doi=10.1007/BF01132596|pages=155–157|first=S. I.|last=Venetskii|s2cid=241230590 }}</ref> The discovery of osmium is intertwined with that of platinum and the other metals of the [[platinum group]]. Platinum reached Europe as ''platina'' ("small silver"), first encountered in the late 17th century in silver mines around the [[Chocó Department]], in [[Colombia]].<ref>{{cite journal|title=The Platinum of New Granada: Mining and Metallurgy in the Spanish Colonial Empire|author=McDonald, M.|journal=Platinum Metals Review|volume=3|issue=4|date=959|pages=140–145|doi=10.1595/003214059X34140145 |url=http://www.platinummetalsreview.com/dynamic/article/view/pmr-v3-i4-140-145|access-date=October 15, 2008|archive-url=https://web.archive.org/web/20110609195507/http://www.platinummetalsreview.com/dynamic/article/view/pmr-v3-i4-140-145|archive-date=June 9, 2011|url-access=subscription}}</ref> The discovery that this metal was not an alloy, but a distinct new element, was published in 1748.<ref>{{cite book|author=Juan, J.|author2=de Ulloa, A.|date=1748|title=Relación histórica del viage a la América Meridional|volume=1|page=606|language=es}}</ref>
Chemists who studied platinum dissolved it in [[aqua regia]] (a mixture of [[hydrochloric acid|hydrochloric]] and [[nitric acid]]s) to create soluble salts. They always observed a small amount of a dark, insoluble residue.<ref name="hunt" /> [[Joseph Louis Proust]] thought that the residue was [[graphite]].<ref name="hunt">{{cite journal|title=A History of Iridium|first=L. B.|last=Hunt|journal=Platinum Metals Review|volume=31|issue=1|date=1987|url=http://www.platinummetalsreview.com/pdf/pmr-v31-i1-032-041.pdf|access-date=2012-03-15|pages=32–41|doi=10.1595/003214087X3113241 |archive-date=March 4, 2012|archive-url=https://web.archive.org/web/20120304225507/http://www.platinummetalsreview.com/pdf/pmr-v31-i1-032-041.pdf}}</ref> [[Victor Collet-Descotils]], [[Antoine François, comte de Fourcroy]], and [[Louis Nicolas Vauquelin]] also observed iridium in the black platinum residue in 1803, but did not obtain enough material for further experiments.<ref name="hunt" /> Later the two French chemists Fourcroy and Vauquelin identified a metal in a platinum residue they called ''ptène''.<ref>{{Cite journal|last1=Haubrichs|first1=Rolf|last2=Zaffalon|first2=Pierre-Leonard|date=2017|title=Osmium vs. 'Ptène': The Naming of the Densest Metal|journal=Johnson Matthey Technology Review|volume=61|issue=3|page=190|doi=10.1595/205651317x695631|doi-access=free}}</ref>

In 1803, [[Smithson Tennant]] analyzed the insoluble residue and concluded that it must contain a new metal. Vauquelin treated the powder alternately with alkali and acids<ref name="Emsley" /> and obtained a volatile new oxide, which he believed was of this new metal—which he named ''ptene'', from the Greek word {{lang|el|πτηνος}} (ptènos) for winged.<ref name="griffith">{{cite journal|doi=10.1595/147106704X4844|title=Bicentenary of Four Platinum Group Metals. Part II: Osmium and iridium – events surrounding their discoveries|author=Griffith, W. P.|journal=Platinum Metals Review|volume=48|issue=4|date=2004|pages=182–189|doi-access=free}}</ref><ref>{{cite book|title=A System of Chemistry of Inorganic Bodies|url=https://archive.org/details/asystemchemistr08thomgoog|author=Thomson, T.|author-link=Thomas Thomson (chemist)|publisher=Baldwin & Cradock, London; and William Blackwood, Edinburgh|date=1831|page=[https://archive.org/details/asystemchemistr08thomgoog/page/n726 693]}}</ref> However, Tennant, who had the advantage of a much larger amount of residue, continued his research and identified two previously undiscovered elements in the black residue, iridium and osmium.<ref name="hunt" /><ref name="Emsley" /> He obtained a yellow solution (probably of ''cis''–<nowiki>[</nowiki>Os(OH)<sub>2</sub>O<sub>4</sub><nowiki>]</nowiki><sup>2−</sup>) by reactions with [[sodium hydroxide]] at red heat. After acidification he was able to distill the formed OsO<sub>4</sub>.<ref name="griffith" /> He named it osmium after [[Greek language|Greek]] ''osme'' meaning "a smell", because of the chlorine-like and slightly garlic-like smell of the volatile [[osmium tetroxide]].<ref name="weeks">{{cite book|title=Discovery of the Elements|url=https://archive.org/details/discoveryofeleme0000week|url-access=registration|pages=[https://archive.org/details/discoveryofeleme0000week/page/414 414–418]|author=Weeks, M. E.|date= 1968|edition=7|publisher=Journal of Chemical Education|isbn=978-0-8486-8579-9|oclc=23991202}}</ref> Discovery of the new elements was documented in a letter to the [[Royal Society]] on June 21, 1804.<ref name="hunt" /><ref>{{cite journal|title=On Two Metals, Found in the Black Powder Remaining after the Solution of Platina|first=S.|last=Tennant|journal=Philosophical Transactions of the Royal Society|volume=94|date=1804|pages=411–418|jstor=107152|doi=10.1098/rstl.1804.0018|url=https://zenodo.org/record/1432312|doi-access=free|access-date=August 27, 2019|archive-date=May 28, 2023|archive-url=https://web.archive.org/web/20230528180903/https://zenodo.org/record/1432312|url-status=live}}</ref>

[[Uranium]] and osmium were early successful [[catalyst]]s in the [[Haber process]], the [[nitrogen fixation]] reaction of [[nitrogen]] and [[hydrogen]] to produce [[ammonia]], giving enough yield to make the process economically successful. At the time, a group at [[BASF]] led by [[Carl Bosch]] bought most of the world's supply of osmium to use as a catalyst. Shortly thereafter, in 1908, cheaper catalysts based on iron and iron oxides were introduced by the same group for the first pilot plants, removing the need for the expensive and rare osmium.<ref>{{cite book| last = Smil| first = Vaclav| title = Enriching the Earth: Fritz Haber, Carl Bosch, and the Transformation of World Food Production| url = https://books.google.com/books?id=G9FljcEASycC| date = 2004| publisher = MIT Press| isbn = 978-0-262-69313-4| pages = 80–86 }}</ref>

Osmium is now obtained primarily from the processing of [[platinum]] and [[nickel]] ores.<ref name="USGS-YB-2006">{{cite web|url=https://minerals.usgs.gov/minerals/pubs/commodity/platinum/myb1-2006-plati.pdf|publisher=United States Geological Survey USGS|access-date=2008-09-16|title=2006 Minerals Yearbook: Platinum-Group Metals|first=Micheal W.|last=George|archive-date=January 11, 2019|archive-url=https://web.archive.org/web/20190111062032/https://minerals.usgs.gov/minerals/pubs/commodity/platinum/myb1-2006-plati.pdf|url-status=live}}</ref>

== Occurrence ==
[[File:Platinum nuggets.jpg|thumb|Native platinum containing traces of the other [[platinum group]] metals]]

Osmium is one of the [[Abundance of elements in Earth's crust|least abundant]] stable elements in Earth's [[crust (geology)|crust]], with an average mass fraction of 50&nbsp;[[parts-per notation|parts per trillion]] in the [[continental crust]].<ref name="wede">{{cite journal|doi=10.1016/0016-7037(95)00038-2|pages=1217–1232|title=The composition of the continental crust|date=1995|issue=7|author=Wedepohl, Hans K|journal=Geochimica et Cosmochimica Acta|volume=59|bibcode=1995GeCoA..59.1217W|url=https://doi.pangaea.de/10.1594/PANGAEA.841674|access-date=August 27, 2019|archive-date=November 3, 2023|archive-url=https://web.archive.org/web/20231103024424/https://doi.pangaea.de/10.1594/PANGAEA.841674|url-status=live|url-access=subscription}}</ref>

Osmium is found in nature as an uncombined element or in natural [[alloy]]s; especially the iridium–osmium alloys, [[osmiridium]] (iridium rich), and [[iridosmium]] (osmium rich).<ref name="Emsley">{{cite book| last = Emsley| first = J.| title = Nature's Building Blocks: An A-Z Guide to the Elements| date = 2003| publisher = Oxford University Press| location = Oxford, England, UK| isbn = 978-0-19-850340-8| pages = [https://archive.org/details/naturesbuildingb0000emsl/page/199 199–201]| chapter = Osmium| chapter-url = https://archive.org/details/naturesbuildingb0000emsl/page/199}}</ref> In [[nickel]] and [[copper]] deposits, the platinum-group metals occur as [[sulfide]]s (i.e., {{chem2|(Pt,Pd)S}}), [[telluride (chemistry)|tellurides]] (e.g., {{chem2|PtBiTe}}), [[antimonide]]s (e.g., {{chem2|PdSb}}), and [[arsenide]]s (e.g., {{chem2|PtAs2}}); in all these compounds platinum is exchanged by a small amount of iridium and osmium. As with all of the platinum-group metals, osmium can be found naturally in alloys with nickel or [[native copper|copper]].<ref>{{cite journal|doi=10.1016/j.mineng.2004.04.001|journal=Minerals Engineering|volume=17|issue=9–10|date=2004|pages=961–979|title=Characterizing and recovering the platinum group minerals—a review|first=Z.|last=Xiao|author2=Laplante, A. R.|bibcode=2004MiEng..17..961X }}</ref>

Within Earth's crust, osmium, like iridium, is found at highest concentrations in three types of geologic structure: igneous deposits (crustal intrusions from below), [[impact crater]]s, and deposits reworked from one of the former structures. The largest known primary reserves are in the [[Bushveld Igneous Complex]] in [[South Africa]],<ref name="kirk-pt">{{cite book |title=Kirk Othmer Encyclopedia of Chemical Technology |first = R. J.|last=Seymour|author2=O'Farrelly, J. I. |chapter=Platinum-group metals|doi=10.1002/0471238961.1612012019052513.a01.pub2|date=2001|publisher=Wiley|isbn = 978-0-471-23896-6}}</ref> though the large copper–nickel deposits near [[Norilsk#Norilsk-Talnakh nickel deposits|Norilsk]] in [[Russia]], and the [[Sudbury Basin]] in [[Canada]] are also significant sources of osmium. Smaller reserves can be found in the United States.<ref name="kirk-pt" /> The [[alluvial]] deposits used by [[pre-Columbian]] people in the [[Chocó Department]], Colombia, are still a source for platinum-group metals. The second large alluvial deposit was found in the [[Ural Mountains]], Russia, which is still mined.<ref name="USGS-YB-2006" /><ref>{{cite web|url=https://minerals.usgs.gov/minerals/pubs/commodity/platinum/mcs-2008-plati.pdf|publisher=United States Geological Survey USGS|access-date=2008-09-16|title=Commodity Report: Platinum-Group Metals|archive-date=January 11, 2019|archive-url=https://web.archive.org/web/20190111015125/https://minerals.usgs.gov/minerals/pubs/commodity/platinum/mcs-2008-plati.pdf|url-status=live}}</ref>

== Production ==
[[File:Osmium cluster.jpg|thumb|Osmium [[crystal]]s, grown by [[Chemical transport reaction|chemical vapor transport]]]]
Osmium is obtained commercially as a by-product from [[nickel]] and [[copper]] mining and processing. During [[Copper extraction techniques#Electrorefining|electrorefining of copper]] and nickel, noble metals such as silver, gold and the platinum-group metals, together with non-metallic elements such as [[selenium]] and [[tellurium]], settle to the bottom of the cell as ''anode mud'', which forms the starting material for their extraction.<ref name="usgs2008-summary">{{cite journal|author=George, M. W.|title=Platinum-group metals|journal=U.S. Geological Survey Mineral Commodity Summaries|date=2008|url=https://minerals.usgs.gov/minerals/pubs/commodity/platinum/mcs-2008-plati.pdf|access-date=September 16, 2008|archive-date=January 11, 2019|archive-url=https://web.archive.org/web/20190111015125/https://minerals.usgs.gov/minerals/pubs/commodity/platinum/mcs-2008-plati.pdf|url-status=live}}</ref><ref name="MinYb2006">{{cite book|url=https://minerals.usgs.gov/minerals/pubs/commodity/platinum/myb1-2006-plati.pdf|publisher=United States Geological Survey USGS|access-date=2008-09-16|title=2006 Minerals Yearbook: Platinum-Group Metals|first=M. W.|last=George|archive-date=January 11, 2019|archive-url=https://web.archive.org/web/20190111062032/https://minerals.usgs.gov/minerals/pubs/commodity/platinum/myb1-2006-plati.pdf|url-status=live}}</ref> Separating the metals requires that they first be brought into solution. Several methods can achieve this, depending on the separation process and the composition of the mixture. Two representative methods are fusion with [[sodium peroxide]] followed by dissolution in [[aqua regia]], and dissolution in a mixture of [[chlorine]] with [[hydrochloric acid]].<ref name="kirk-pt" /><ref name="ullmann-pt">{{cite book |author=Renner, H. |display-authors=4 |author2=Schlamp, G. |author3=Kleinwächter, I. |author4=Drost, E. |author5=Lüschow, H. M. |author6=Tews, P. |author7=Panster, P. |author8=Diehl, M. |author9=Lang, J. |author10=Kreuzer, T. |author11=Knödler, A. |author12=Starz, K. A. |author13=Dermann, K. |author14=Rothaut, J. |author15=Drieselman, R.|chapter=Platinum group metals and compounds|title=Ullmann's Encyclopedia of Industrial Chemistry |publisher=Wiley|date=2002|doi=10.1002/14356007.a21_075|isbn=978-3-527-30673-2 }}</ref> Osmium, ruthenium, rhodium, and iridium can be separated from platinum, gold, and base metals by their insolubility in aqua regia, leaving a solid residue. Rhodium can be separated from the residue by treatment with molten [[sodium bisulfate]]. The insoluble residue, containing ruthenium, osmium, and iridium, is treated with [[sodium oxide]], in which Ir is insoluble, producing water-soluble ruthenium and osmium salts. After oxidation to the volatile oxides, {{chem|RuO|4}} is separated from {{chem|OsO|4}} by precipitation of (NH<sub>4</sub>)<sub>3</sub>RuCl<sub>6</sub> with ammonium chloride.

After it is dissolved, osmium is separated from the other platinum-group metals by distillation or extraction with organic solvents of the volatile osmium tetroxide.<ref>{{cite journal|title=The Platinum Metals|first=Raleigh|last=Gilchrist|journal=Chemical Reviews|date=1943|volume=32|issue=3|pages=277–372|doi=10.1021/cr60103a002|s2cid=96640406 }}</ref> The first method is similar to the procedure used by Tennant and Wollaston. Both methods are suitable for industrial-scale production. Modern methods involve reducing [[ammonium hexachloroosmate(IV)]] using hydrogen, yielding the metal as a powder or [[metal sponge|sponge]] that can be treated using [[powder metallurgy]] techniques.<ref>{{cite journal|first=L. B.|last=Hunt|author2=Lever, F. M.|journal=Platinum Metals Review|volume=13|issue=4|date=1969|pages=126–138|title=Platinum Metals: A Survey of Productive Resources to industrial Uses|doi=10.1595/003214069X134126138 |url=http://www.platinummetalsreview.com/pdf/pmr-v13-i4-126-138.pdf|access-date=2008-10-02|archive-date=October 29, 2008|archive-url=https://web.archive.org/web/20081029205825/http://www.platinummetalsreview.com/pdf/pmr-v13-i4-126-138.pdf}}</ref>

Estimates of annual worldwide osmium production are on the order of several hundred to a few thousand kilograms.<ref>{{cite journal |last1=Girolami |first1=Gregory |title=Osmium weighs in |journal=Nature Chemistry |date=November 2012 |volume=4 |issue=11 |page=954 |doi=10.1038/nchem.1479|doi-access=free |pmid=23089872 |bibcode=2012NatCh...4..954G }}</ref><ref name="greenwood" /> Production and consumption figures for osmium are not well reported because demand for the metal is limited and can be fulfilled with the byproducts of other refining processes.<ref name="greenwood" /> To reflect this, statistics often report osmium with other minor platinum group metals such as iridium and ruthenium. US imports of osmium from 2014 to 2021 averaged 155&nbsp;kg annually.<ref>{{cite web |author1=Singerling, S.A. |author2=Schulte, R.F. |title=2018 Minerals Yearbook: Platinum-Group Metals [Advance Release] |url=https://www.usgs.gov/centers/national-minerals-information-center/platinum-group-metals-statistics-and-information |website=Platinum-Group Metals Statistics and Information |publisher=U.S. Geological Survey |archive-url=https://web.archive.org/web/20230714121323/https://www.usgs.gov/centers/national-minerals-information-center/platinum-group-metals-statistics-and-information |archive-date=July 14, 2023 |date=August 2021 |access-date=September 24, 2023 |url-status=bot: unknown }}</ref><ref>{{cite web |last1=Schulte |first1=R.F. |title=Mineral commodity summaries 2022 - Platinum-Group Metals |url=https://www.usgs.gov/centers/national-minerals-information-center/platinum-group-metals-statistics-and-information |website=Platinum-Group Metals Statistics and Information |publisher=U.S. Geological Survey |archive-url=https://web.archive.org/web/20230714121323/https://www.usgs.gov/centers/national-minerals-information-center/platinum-group-metals-statistics-and-information |archive-date=July 14, 2023 |access-date=September 24, 2023 |url-status=bot: unknown }}</ref>

== Applications ==
Because osmium is virtually unforgeable when fully dense and very fragile when [[sintering|sintered]], it is rarely used in its pure state, but is instead often alloyed with other metals for high-wear applications. Osmium alloys such as [[osmiridium]] are very hard and, along with other platinum-group metals, are used in the tips of [[fountain pen]]s, instrument pivots, and electrical contacts, as they can resist wear from frequent operation. They were also used for the tips of [[phonograph#Stylus|phonograph styli]] during the late 78&nbsp;[[Revolutions per minute|rpm]] and early "[[LP record|LP]]" and "[[Single (music)|45]]" record era, circa 1945 to 1955. Osmium-alloy tips were significantly more durable than steel and chromium needle points, but wore out far more rapidly than competing, and costlier, [[sapphire]] and [[diamond]] tips, so they were discontinued.<ref>{{cite book| author = Cramer, Stephen D. | author2 = Covino, Bernard S. Jr.| name-list-style = amp| title = ASM Handbook Volume 13B. Corrosion: Materials| url = https://books.google.com/books?id=wGdFAAAAYAAJ| date = 2005| publisher = ASM International| isbn = 978-0-87170-707-9 }}</ref>

Only two osmium compounds have major applications: osmium tetroxide for [[staining]] tissue in [[electron microscopy]] and for the oxidation of [[alkenes]] in [[organic synthesis]], and the non-volatile osmates for [[Sharpless asymmetric dihydroxylation|organic oxidation reactions]].<ref name="Bozzola" />

[[Osmium tetroxide]] has been used in [[fingerprint]] detection<ref>{{cite journal|title=The Use of Hydrogen Fluoride in the Development of Latent Fingerprints Found on Glass Surfaces|first=Herbert L.|last=MacDonell|journal=The Journal of Criminal Law, Criminology, and Police Science|volume=51|issue=4|date=1960|pages=465–470|jstor=1140672|doi=10.2307/1140672|url=https://scholarlycommons.law.northwestern.edu/cgi/viewcontent.cgi?article=4971&context=jclc|access-date=December 2, 2018|archive-date=September 28, 2023|archive-url=https://web.archive.org/web/20230928161103/https://scholarlycommons.law.northwestern.edu/cgi/viewcontent.cgi?article=4971&context=jclc|url-status=live|url-access=subscription}}</ref> and in staining [[fat]]ty tissue for optical and [[electron microscopy]]. As a strong oxidant, it cross-links lipids mainly by reacting with unsaturated carbon–carbon bonds and thereby both fixes [[biological membrane]]s in place in tissue samples and simultaneously stains them. Because osmium atoms are extremely electron-dense, osmium staining greatly enhances image contrast in [[transmission electron microscopy]] (TEM) studies of biological materials. Those carbon materials otherwise have very weak TEM contrast.<ref name="Bozzola">{{cite book| author2 = Russell, Lonnie D.| last = Bozzola| first = John J.| title = Electron microscopy: principles and techniques for biologists| chapter-url = https://books.google.com/books?id=zMkBAPACbEkC&pg=PA21| date = 1999| publisher = Jones and Bartlett| location = Sudbury, Mass.| isbn = 978-0-7637-0192-5| pages = 21–31| chapter = Specimen Preparation for Transmission Electron Microscopy }}</ref> Another osmium compound, osmium ferricyanide (OsFeCN), exhibits similar fixing and staining action.<ref>{{cite book| author = Chadwick, D.| title = Role of the sarcoplasmic reticulum in smooth muscle| date = 2002| publisher = John Wiley and Sons| isbn = 978-0-470-84479-3| pages = [https://archive.org/details/roleofsarcoplasm0000unse/page/259 259–264]| url-access = registration| url = https://archive.org/details/roleofsarcoplasm0000unse/page/259}}</ref>

The tetroxide and its derivative [[potassium osmate]] are important oxidants in [[organic synthesis]]. For the [[Sharpless asymmetric dihydroxylation]], which uses osmate for the conversion of a [[double bond]] into a [[Vicinal (chemistry)|vicinal]] [[diol]], [[Karl Barry Sharpless]] was awarded the [[Nobel Prize in Chemistry]] in 2001.<ref>{{cite journal|last=Kolb|first=H. C.|author2=Van Nieuwenhze, M. S.|author3=Sharpless, K. B.|journal=Chemical Reviews|date=1994|volume=94|issue=8|pages=2483–2547|doi=10.1021/cr00032a009|title=Catalytic Asymmetric Dihydroxylation}}</ref><ref>{{cite journal|title=2001 Nobel Prize in Chemistry|last=Colacot|first=T. J.|journal=Platinum Metals Review|volume=46|issue=2|date=2002|pages=82–83|doi=10.1595/003214002X4628283 |url=http://www.platinummetalsreview.com/pdf/pmr-v46-i2-082-083.pdf|access-date=June 12, 2009|archive-date=January 31, 2013|archive-url=https://web.archive.org/web/20130131104016/http://www.platinummetalsreview.com/pdf/pmr-v46-i2-082-083.pdf}}</ref> OsO<sub>4</sub> is very expensive for this use, so KMnO<sub>4</sub> is often used instead, even though the yields are less for this cheaper chemical reagent.

In 1898, the Austrian chemist [[Carl Auer von Welsbach|Auer von Welsbach]] developed the Oslamp with a [[Electrical filament|filament]] made of osmium, which he introduced commercially in 1902. After only a few years, osmium was replaced by [[tungsten]], which is more abundant (and thus cheaper) and more stable. Tungsten has the highest melting point among all metals, and its use in light bulbs increases the luminous efficacy and life of [[incandescent lamp]]s.<ref name="griffith" />

The light bulb manufacturer [[Osram]] (founded in 1906, when three German companies, Auer-Gesellschaft, AEG and Siemens & Halske, combined their lamp production facilities) derived its name from the elements of '''os'''mium and ''Wolf'''ram''''' (the latter is German for tungsten).<ref>{{cite journal|title=Scanning our past from London: the filament lamp and new materials|first=B.|journal=Proceedings of the IEEE|date=2001|volume=89|issue=3|pages=413–415|doi=10.1109/5.915382|last=Bowers, B.|bibcode=2001IEEEP..89..413B |s2cid=28155048}}</ref>

Like [[palladium]], powdered osmium effectively adsorbs hydrogen atoms. This could make osmium a potential candidate for a metal-hydride battery electrode. However, osmium is expensive and would react with potassium hydroxide, the most common battery electrolyte.<ref>{{cite journal|title=The Solubility of Hydrogen in the Platinum Metals under High Pressure|first=V. E.|last=Antonov|author2=Belash, I. T.|author3=Malyshev, V. Yu.|author4=Ponyatovsky, E. G.|journal=Platinum Metals Review|volume=28|issue=4|date=1984|pages=158–163|doi=10.1595/003214084X284158163 |url=http://www.platinummetalsreview.com/pdf/pmr-v28-i4-158-163.pdf|access-date=June 4, 2009|archive-date=January 31, 2013|archive-url=https://web.archive.org/web/20130131165432/http://www.platinummetalsreview.com/pdf/pmr-v28-i4-158-163.pdf}}</ref>

Osmium has high [[reflectivity]] in the [[ultraviolet]] range of the [[electromagnetic spectrum]]; for example, at 600&nbsp;[[Ångström|Å]] osmium has a reflectivity twice that of gold.<ref>{{cite journal|doi=10.1364/AO.24.002959|title=Osmium coated diffraction grating in the Space Shuttle environment: performance|date=1985|author=Torr, Marsha R.|journal=Applied Optics|volume=24|page=2959|pmid=18223987|issue=18|bibcode=1985ApOpt..24.2959T }}</ref> This high reflectivity is desirable in space-based [[Ultraviolet-visible spectroscopy|UV spectrometers]], which have reduced mirror sizes due to space limitations. Osmium-coated mirrors were flown in several space missions aboard the [[Space Shuttle]], but it soon became clear that the oxygen radicals in [[low Earth orbit]] are abundant enough to significantly deteriorate the osmium layer.<ref>{{cite journal|doi=10.1364/AO.24.002660|title=Low earth orbit environmental effects on osmium and related optical thin-film coatings|date=1985|author=Gull, T. R.|journal=Applied Optics|volume=24|page=2660|pmid=18223936|last2=Herzig|first2=H.|last3=Osantowski|first3=J. F.|last4=Toft|first4=A. R.|issue=16|bibcode=1985ApOpt..24.2660G }}</ref>

<gallery widths="200" heights="200">
File:Sharpless Dihydroxylation Scheme.png|The Sharpless dihydroxylation:<br /> R<sub>L</sub> = largest substituent; R<sub>M</sub> = medium-sized substituent; R<sub>S</sub> = smallest substituent
File:NASAmirroroxidation.jpg|Post-flight appearance of Os, Ag, and Au mirrors from the front (left images) and rear panels of the Space Shuttle. Blackening reveals oxidation due to irradiation by oxygen atoms.<ref>{{cite web|publisher=NASA|last1=Linton|first1=Roger C.|last2=Kamenetzky|first2=Rachel R.|url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930019094_1993019094.pdf|title=Second LDEF post-retrieval symposium interim results of experiment A0034|access-date=2009-06-06|year=1992|archive-date=November 4, 2023|archive-url=https://web.archive.org/web/20231104100732/https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930019094_1993019094.pdf|url-status=live}}</ref><ref>{{cite journal|title=LDEF experiment A0034: Atomic oxygen stimulated outgassing|bibcode=1992ldef.symp..763L|last1=Linton|first1=Roger C.|last2=Kamenetzky|first2=Rachel R.|last3=Reynolds|first3=John M.|last4=Burris|first4=Charles L.|date=1992|page=763|journal=NASA Langley Research Center}}</ref>
File:Osmium-2.jpg|A bead of osmium, about 0.5 cm in diameter, displaying the metal's reflectivity
</gallery>

== Precautions ==
The primary hazard presented by metallic osmium is the potential formation of [[osmium tetroxide]] (OsO<sub>4</sub>), which is [[Volatility (chemistry)|volatile]] and very poisonous.<ref>{{cite book |last1=Lebeau |first1=Alex |title=Hamilton & Hardy's Industrial Toxicology |date=20 March 2015 |publisher=John Wiley & Sons, Inc. |isbn=978-1-118-83401-5 |pages=187–192 |language=en |chapter=Platinum Group Elements: Palladium, Iridium, Osmium, Rhodium, and Ruthenium}}</ref> This reaction is thermodynamically favorable at room temperature,<ref>{{cite web |title=Osmium(VIII) oxide |url=https://hbcp.chemnetbase.com/ |website=CRC Handbook of Chemistry and Physics, 103rd Edition (Internet Version 2022) |publisher=CRC Press/Taylor & Francis Group |access-date=6 February 2023 |archive-date=October 28, 2023 |archive-url=https://web.archive.org/web/20231028215703/https://hbcp.chemnetbase.com/contents/ContentsSearch.xhtml?dswid=7699 |url-status=live }}</ref> but the rate depends on the temperature and surface area of the metal.<ref name="Toxic Manifestations of Osmium Tetr">{{cite journal |last1=McLaughlin |first1=A. I. G. |last2=Milton |first2=R. |last3=Perry |first3=Kenneth M. A. |title=Toxic Manifestations of Osmium Tetroxide |journal=Occupational and Environmental Medicine |date=1 July 1946 |volume=3 |issue=3 |pages=183–186 |doi=10.1136/oem.3.3.183|pmid=20991177 |pmc=1035752 }}</ref><ref>{{cite journal |last1=Friedova |first1=Natalie |last2=Pelclova |first2=Daniela |last3=Obertova |first3=Nikola |last4=Lach |first4=Karel |last5=Kesslerova |first5=Katerina |last6=Kohout |first6=Pavel |title=Osmium absorption after osmium tetroxide skin and eye exposure |journal=Basic & Clinical Pharmacology & Toxicology |date=November 2020 |volume=127 |issue=5 |pages=429–433 |doi=10.1111/bcpt.13450|pmid=32524772 |s2cid=219588237 }}</ref> As a result, bulk material is not considered hazardous<ref name="Toxic Manifestations of Osmium Tetr"/><ref>{{cite book |title=Sax's Dangerous Properties of Industrial Materials |date=15 October 2012 |publisher=John Wiley & Sons, Inc. |isbn=978-0-471-70134-7 |language=en |chapter=Osmium 7440-04-2|pages=1–2 |doi=10.1002/0471701343.sdp45229 }}</ref><ref>{{cite journal |last1=Luttrell |first1=William E. |last2=Giles |first2=Cory B. |title=Toxic tips: Osmium tetroxide |journal=Journal of Chemical Health & Safety |date=1 September 2007 |volume=14 |issue=5 |pages=40–41 |doi=10.1016/j.jchas.2007.07.003}}</ref><ref>{{cite journal |last1=Smith |first1=Ivan C. |last2=Carson |first2=Bonnie L. |last3=Ferguson |first3=Thomas L. |title=Osmium: An Appraisal of Environmental Exposure |journal=Environmental Health Perspectives |date=August 1974 |volume=8 |pages=201–213 |doi=10.1289/ehp.748201 |pmid=4470919 |pmc=1474945 |bibcode=1974EnvHP...8..201S |language=en |issn=0091-6765}}</ref> while powders react quickly enough that samples can sometimes smell like OsO<sub>4</sub> if they are handled in air.<ref name="greenwood" /><ref>{{cite web |last1=Gadaskina |first1=I. D. |title=Osmium |url=https://www.iloencyclopaedia.org/part-ix-21851/metals-chemical-properties-and-toxicity/item/178-osmium |website=ILO Encyclopaedia of Occupational Health and Safety |access-date=6 February 2023 |language=en-gb |archive-date=November 3, 2023 |archive-url=https://web.archive.org/web/20231103014706/https://www.iloencyclopaedia.org/part-ix-21851/metals-chemical-properties-and-toxicity/item/178-osmium |url-status=live }}</ref>

== Price ==
Between 1990 and 2010, the nominal price of osmium metal was almost constant, while inflation reduced the real value from ~US{{convert|950|$/ozt|$/kg}} to ~US{{convert|600|$/ozt|$/kg}}<ref name="sv-usgs-2012">{{cite web |title=USGS Scientific Investigations Report 2012–5188: Metal Prices in the United States Through 2010 |url=https://pubs.usgs.gov/sir/2012/5188 |website=pubs.usgs.gov |publisher=U.S. Geological Survey |access-date=11 July 2023 |pages=119–128 |date=2013 |archive-date=November 7, 2023 |archive-url=https://web.archive.org/web/20231107214738/https://pubs.usgs.gov/sir/2012/5188/ |url-status=live }}</ref> Because osmium has few commercial applications, it is not heavily traded and prices are seldom reported.<ref name="sv-usgs-2012" />

== Notes ==
{{notelist}}

== References ==
{{reflist|30em}}

== Cited sources ==
* {{cite book |editor-last=Haynes |editor-first=William M. |year=2011 |title=CRC Handbook of Chemistry and Physics |title-link=CRC Handbook of Chemistry and Physics |edition=92nd |publisher=[[CRC Press]] |isbn=978-1-4398-5511-9}}

== External links ==
{{Commons|Osmium}}
{{Wiktionary|osmium}}
* [http://www.periodicvideos.com/videos/076.htm Osmium] {{Webarchive|url=https://web.archive.org/web/20130322195133/http://periodicvideos.com/videos/076.htm |date=March 22, 2013 }} at ''[[The Periodic Table of Videos]]'' (University of Nottingham)
* Flegenheimer, J. (2014). [https://web.archive.org/web/20150619170958/http://www.uff.br/RVQ/index.php/rvq/article/viewFile/660/450 "The Mystery of the Disappearing Isotope"] (via the Wayback Machine). ''Revista Virtual de Química''. V. XX.
* {{cite EB1911|wstitle=Osmium|volume=20|page=352}}

{{Periodic table (navbox)}}
{{Osmium compounds}}
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[[Category:Osmium| ]]
[[Category:Chemical elements with hexagonal close-packed structure]]
[[Category:Chemical elements]]
[[Category:Native element minerals]]
[[Category:Noble metals]]
[[Category:Platinum-group metals]]
[[Category:Precious metals]]
[[Category:Transition metals]]