View source for Pyrite

{{Short description|Iron (II) disulfide mineral}}
{{distinguish|text = [[Synthesis of precious metals#Gold|Synthetic gold]]}}
{{Redirect|Fool's Gold}}
{{About|iron pyrite|other pyrite minerals|Pyrite group}}

{{Infobox mineral
| name        = Pyrite
| category    = [[Sulfide mineral]]
| boxbgcolor  =
| image       = Pyrite - Huanzala mine, Huallanca, Bolognesi, Ancash, Peru.jpg
| imagesize   = 260px
| caption     = Intergrowth of lustrous, cubic crystals of pyrite, with some surfaces showing characteristic striations, from Huanzala mine, Ancash, Peru. Specimen size: 7.0 × 5.0 × 2.5&nbsp;cm
| formula     = FeS<sub>2</sub>
| IMAsymbol   = Py<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3 |pages=291–320|doi=10.1180/mgm.2021.43 |bibcode=2021MinM...85..291W |s2cid=235729616 |doi-access=free}}</ref>
| molweight   = 119.98 g/mol
| strunz      = 2.EB.05a
| dana        = 2.12.1.1
| system      = [[Cubic (crystal system)|Cubic]]
| class       = Diploidal (m{{overline|3}}) <br/>[[H-M symbol]]: (2/m {{overline|3}})
| symmetry    = ''P''a{{overline|3}}
| unit cell   = a = 5.417&nbsp;[[Ångstrom|Å]], Z&nbsp;=&nbsp;4
| color       = Pale brass-yellow reflective; tarnishes darker and iridescent
| habit       = Cubic, faces may be striated, but also frequently octahedral and pyritohedral. Often inter-grown, massive, radiated, granular, globular, and stalactitic.
| twinning    = Penetration and contact twinning
| cleavage    = Indistinct on {001}; partings on {011} and {111}
| fracture    = Very uneven, sometimes conchoidal
| tenacity    = Brittle
| mohs        = 6–6.5
| luster      = Metallic, glistening
| refractive  =
| opticalprop =
| birefringence =
| pleochroism =
| streak      = Greenish-black to brownish-black
| gravity     = 4.95–5.10
| density     = 4.8–5 g/cm<sup>3</sup>
| melt        =
| fusibility  = 2.5–3 to a magnetic globule
| diagnostic  =
| solubility  = Insoluble in water
| diaphaneity = Opaque
| other       = [[diamagnetism|Diamagnetic]] to [[paramagnetism|paramagnetic]]
| references  =<ref name=Hurlbut>{{cite book |author1=Hurlbut, Cornelius S. |author2=Klein, Cornelis |year=1985 |title=Manual of Mineralogy |edition=20th |publisher=John Wiley and Sons |location=New York, NY |pages=[https://archive.org/details/manualofmineralo00klei/page/285 285–286] |isbn=978-0-471-80580-9 |url-access=registration |url=https://archive.org/details/manualofmineralo00klei/page/285 }}</ref><ref>{{cite web |url=http://webmineral.com/data/Pyrite.shtml |title=Pyrite |website=Webmineral.com |access-date=2011-05-25}}</ref><ref>{{cite web |url=http://www.mindat.org/min-3314.html |title=Pyrite |website=Mindat.org |access-date=2011-05-25}}</ref><ref>{{cite book|editor=Anthony, John W. |editor2=Bideaux, Richard A. |editor3=Bladh, Kenneth W. |editor4=Nichols, Monte C. |title= Handbook of Mineralogy|publisher= Mineralogical Society of America|place= Chantilly, Virginia, US|chapter-url=http://rruff.geo.arizona.edu/doclib/hom/pyrite.pdf|chapter=Pyrite |isbn=978-0962209734 |volume=I (Elements, Sulfides, Sulfosalts)|year=1990}}</ref>
}}

The [[mineral]] '''pyrite''' ({{IPAc-en|ˈ|p|aɪ|r|aɪ|t}} {{respell|PY|ryte}}),<ref>{{Cite web|url=https://dictionary.cambridge.org/dictionary/english/pyrite|title=Pyrite &#124; meaning in the Cambridge English Dictionary|website=dictionary.cambridge.org}}</ref> or '''iron pyrite''', also known as '''fool's gold''', is an [[iron sulfide]] with the [[chemical formula]] [[Iron|Fe]][[Sulfur|S]]<sub>2</sub> (iron (II) disulfide).<!-- Per section on oxidation states, iron (II) is correct. The sulfur is present as persulfide ion.--> Pyrite is the most abundant [[sulfide mineral]].<ref>{{cite book |url=https://books.google.com/books?id=0mXxAAAAMAAJ&pg=PA137 |page=137 |title=Sulfide Deposits in the Coosa Valley Area, Georgia |author1=Vernon J. Hurst |author2=Thomas J. Crawford |publisher=Economic Development Administration, Technical Assistance Project, U. S. Department of Commerce |year=1970}}</ref>
[[File:2780M-pyrite1.jpg|thumb|Pyrite cubic crystals on [[marl]] from [[Navajún]], [[La Rioja (Spain)|La Rioja]], Spain (size: {{convert|95|by|78|mm|disp=sqbr}}, {{convert|512|g|disp=sqbr}}; main crystal: {{convert|31|mm|disp=sqbr}} on edge)]]
Pyrite's metallic [[Lustre (mineralogy)|luster]] and pale brass-yellow [[hue]] give it a superficial resemblance to [[gold]], hence the well-known nickname of ''fool's gold''. The color has also led to the nicknames ''brass'', ''brazzle'', and ''brazil'', primarily used to refer to pyrite found in [[coal]].<ref>{{cite book |author1=Jackson, Julia A. |author2=Mehl, James |author3=Neuendorf, Klaus |url=https://books.google.com/books?id=SfnSesBc-RgC&pg=PA82 |via=Google Books |title=Glossary of Geology |publisher=American Geological Institute |year=2005 |page=82|isbn=9780922152766 }}</ref><ref>{{cite book |author=Fay, Albert H. |url=https://books.google.com/books?id=fB4bAAAAYAAJ&pg=PA103 |via=Google Books |title=A Glossary of the Mining and Mineral Industry |publisher=United States Bureau of Mines |year=1920 |pages=103–104}}</ref>

The name ''pyrite'' is derived from the [[Greek language|Greek]] {{lang|grc|πυρίτης λίθος}} ({{lang|grc-Latn|pyritēs lithos}}), 'stone or mineral which strikes fire',<ref>{{LSJ|puri/ths1|πυρίτης|ref}}.</ref> in turn from {{lang|grc|πῦρ}} ({{lang|grc-Latn|pŷr}}), 'fire'.<ref>{{LSJ|pu{{=}}r|πῦρ|shortref}}.</ref> In ancient Roman times, this name was applied to several types of stone that would create sparks when struck against [[steel]]; [[Pliny the Elder]] described one of them as being brassy, almost certainly a reference to what is now called pyrite.<ref>{{cite book |author1=Dana, James Dwight |author2=Dana, Edward Salisbury |url=https://books.google.com/books?id=lHS7AAAAIAAJ&pg=PA86 |title=Descriptive Mineralogy |edition=6th |publisher=Wiley |location=New York |year=1911 |page=86}}</ref>

By [[Georgius Agricola]]'s time, {{circa|1550}}, the term had become a generic term for all of the [[pyrite group|sulfide minerals]].<ref>{{cite magazine |translator1=Hoover, H.C. |translator1-link=Herbert Clark Hoover |translator2=Hoover, L.H. |translator2-link=Lou Henry Hoover |title=De re metallica |magazine=The Mining Magazine |location=London |orig-year=1912 |publisher=Dover |year=1950 |at=see footnote on p 112|title-link=De re metallica }}</ref>

[[File:Pyrite under Normal and Polarized light.jpg|thumb|Pyrite under normal and polarized light]]
Pyrite is usually found associated with other sulfides or [[oxide]]s in [[quartz]] [[Vein (geology)|veins]], [[sedimentary rock]], and [[metamorphic rock]], as well as in coal beds and as a replacement mineral in [[fossil]]s, but has also been identified in the [[sclerite]]s of [[Scaly-foot snail|scaly-foot gastropods]].<ref>{{cite news |url=http://news.nationalgeographic.com/news/2003/11/1107_031107_snailarmor.html |archive-url=https://web.archive.org/web/20031110015525/http://news.nationalgeographic.com/news/2003/11/1107_031107_snailarmor.html |url-status=dead |archive-date=November 10, 2003 |title=Armor-plated snail discovered in deep sea |website=news.nationalgeographic.com |access-date=2016-08-29 |publisher=National Geographic Society |location=Washington, DC}}</ref> Despite being nicknamed "fool's gold", pyrite is sometimes found in association with small quantities of gold. A substantial proportion of the gold is "invisible gold" incorporated into the pyrite (see [[Carlin-type gold deposit]]). It has been suggested that the presence of both gold and [[arsenic]] is a case of [[coupled substitution]] but as of 1997 the chemical state of the gold remained controversial.<ref>{{cite journal |author1=Fleet, M. E. |author2=Mumin, A. Hamid |url=http://www.minsocam.org/msa/AmMin/toc/Articles_Free/1997/Fleet_p182-193_97.pdf |title=Gold-bearing arsenian pyrite and marcasite and arsenopyrite from Carlin Trend gold deposits and laboratory synthesis |journal=American Mineralogist |volume=82 |issue=1–2 |year=1997 |pages=182–193|doi=10.2138/am-1997-1-220 |bibcode=1997AmMin..82..182F |s2cid=55899431 }}</ref>

== Uses ==
[[File:Stolna pri Perneku.jpg|thumbnail|left|An abandoned pyrite mine near [[Pernek]] in [[Slovakia]]]]

Pyrite gained a brief popularity in the 16th and 17th&nbsp;centuries as a source of [[Combustion|ignition]] in early [[firearm]]s, most notably the [[wheellock]], where a sample of pyrite was placed against a circular file to strike the sparks needed to fire the gun.<ref>{{Cite book|last=Larson|first=Bruce|date=2003|title=An Interpretation of Firearms in the Archaeological Record in Virginia 1607-1625|chapter=Firearms|chapter-url=https://link.gale.com/apps/doc/CX2831100051/GVRL?u=lond95336&sid=GVRL&xid=edf7e554|series=Dissertations, Theses, and Masters Projects|volume=1|pages=413–418}}</ref>

Pyrite is used with [[flint]]stone and a form of [[tinder]] made of [[stringybark]] by the [[Kaurna people]] of [[South Australia]], as a traditional method of starting fires.<ref>{{cite web | last=Schultz | first=Chester | title=Place Name Summary 6/23: Brukangga and Tindale's uses of the word bruki | website=Adelaide Research & Scholarship | publisher=[[University of Adelaide]] | date=22 October 2018 | url=https://www.adelaide.edu.au/kwp/placenames/research-publ/6-23Brukangga.pdf | access-date=16 November 2020 | archive-date=10 September 2021 | archive-url=https://web.archive.org/web/20210910191311/https://www.adelaide.edu.au/kwp/placenames/research-publ/6-23Brukangga.pdf | url-status=dead }}</ref>

Pyrite has been used since classical times to manufacture ''copperas'' ([[Iron(II) sulfate|ferrous sulfate]]). Iron pyrite was heaped up and allowed to weather (an example of an early form of [[heap leaching]]). The acidic runoff from the heap was then boiled with iron to produce iron sulfate. In the 15th century, new methods of such leaching began to replace the burning of sulfur as a source of [[sulfuric acid]]. By the 19th&nbsp;century, it had become the dominant method.<ref>{{cite journal |title=Industrial England in the Middle of the Eighteenth Century |journal=Nature |volume=83 |issue=2113 |date=1910-04-28 |pages=264–268 |doi=10.1038/083264a0|bibcode = 1910Natur..83..264. |hdl=2027/coo1.ark:/13960/t63497b2h |s2cid=34019869 |url=https://archive.org/details/industrialenglan00woodrich |hdl-access=free }}</ref>

Pyrite remains in commercial use for the production of [[sulfur dioxide]], for use in such applications as the [[Pulp and paper industry|paper industry]], and in the manufacture of sulfuric acid. Thermal decomposition of pyrite into FeS ([[iron(II) sulfide]]) and elemental sulfur starts at {{cvt|540|C|||}}; at around {{cvt|700|C|||}}, ''p''<sub>S<sub>2</sub></sub> is about {{nowrap|1 atm}}.<ref>{{cite book |title=Principles of extractive metallurgy |author=Rosenqvist, Terkel |edition=2nd |publisher=Tapir Academic Press |year=2004 |isbn=978-82-519-1922-7 |page=52 |url=https://books.google.com/books?id=I2mg2ine4AEC&pg=PA52 }}</ref>

A newer commercial use for pyrite is as the [[cathode]] material in [[Energizer]] brand non-rechargeable [[Lithium metal battery|lithium metal batteries]].<ref>{{cite book |publisher=Energizer Corporation |url=http://data.energizer.com/PDFs/lithiuml91l92_appman.pdf |title=Lithium-Iron Disulfide (Li-FeS<sub>2</sub>) |series=Handbook and Application Manual |date=2017-09-19 |article=Cylindrical Primary Lithium [battery] |access-date=2018-04-20 |archive-date=2006-03-17 |archive-url=https://web.archive.org/web/20060317180835/http://data.energizer.com/PDFs/lithiuml91l92_appman.pdf |url-status=dead }}</ref>

Pyrite is a [[semiconductor material]] with a [[band gap]] of 0.95 [[Electronvolt|eV]].<ref>{{cite journal |url=http://www.esqsec.unibe.ch/%5Cpub%5Cpub_51.htm |title=Iron Disulfide (Pyrite) as Photovoltaic Material: Problems and Opportunities |author1=Ellmer, K. |author2=Tributsch, H. |name-list-style=amp |journal=Proceedings of the 12th Workshop on Quantum Solar Energy Conversion – (QUANTSOL 2000) |date=2000-03-11 |url-status=dead |archive-url=https://web.archive.org/web/20100115000025/http://www.esqsec.unibe.ch/pub/pub_51.htm |archive-date=2010-01-15 }}</ref> Pure pyrite is naturally n-type, in both crystal and thin-film forms, potentially due to sulfur vacancies in the pyrite crystal structure acting as n-dopants.<ref name="auto">{{cite journal |title=Potential resolution to the doping puzzle in iron pyrite: Carrier type determination by Hall effect and thermopower |author1=Xin Zhang |author2=Mengquin Li |name-list-style=amp |journal=Physical Review Materials |volume=1 |date=2017-06-19 |issue=1 |page=015402 |doi=10.1103/PhysRevMaterials.1.015402 |bibcode=2017PhRvM...1a5402Z |doi-access=free }}</ref>

During the early years of the 20th&nbsp;century, pyrite was used as a [[Cat's-whisker detector|mineral detector]] in [[radio]] receivers, and is still used by [[crystal radio]] hobbyists. Until the [[vacuum tube]] matured, the crystal detector was the most sensitive and dependable [[detector (radio)|detector]] available—with considerable variation between mineral types and even individual samples within a particular type of mineral. Pyrite detectors occupied a midway point between [[galena]] detectors and the more mechanically complicated [[Cat's-whisker detector#Types|perikon]] mineral pairs. Pyrite detectors can be as sensitive as a modern 1N34A [[germanium]] [[diode]] detector.<ref>{{cite book |url=https://books.google.com/books?id=eSguAAAAYAAJ&pg=PA302 |title=The Principles Underlying Radio Communication |series=Radio Pamphlet |volume=40 |department=U.S. Army Signal Corps |date=1918 |at=section&nbsp;179, pp 302–305 |via=Google Books}}</ref><ref>{{cite book |author=Thomas H. Lee |url=https://books.google.com/books?id=DzcMK-2mFQUC&pg=PA4 |title=The Design of Radio Frequency Integrated Circuits |edition=2nd |publisher=Cambridge University Press |location=Cambridge, UK |year=2004 |pages=4–6 |via=Google Books|isbn=9780521835398 }}</ref>

Pyrite has been proposed as an abundant, non-toxic, inexpensive material in low-cost [[photovoltaic]] solar panels.<ref>{{cite journal |title=Materials availability expands the opportunity for large-scale photovoltaics deployment |year=2009 |last1=Wadia |first1=Cyrus |last2=Alivisatos |first2=A. Paul |last3=Kammen |first3=Daniel M. |journal=Environmental Science & Technology |volume=43 |issue=6 |pages=2072–7 |doi=10.1021/es8019534 |bibcode=2009EnST...43.2072W |pmid=19368216|s2cid=36725835 }}</ref> Synthetic iron sulfide was used with [[copper sulfide]] to create the photovoltaic material.<ref>{{cite news |url=http://www.berkeley.edu/news/media/releases/2009/02/17_solar.shtml |title=Cheaper materials could be key to low-cost solar cells |publisher=University of California – Berkeley |location=Berkeley, CA |author=Sanders, Robert |date=17 February 2009}}</ref> More recent efforts are working toward thin-film solar cells made entirely of pyrite.<ref name="auto"/>

Pyrite is used to make [[marcasite jewelry]]. Marcasite jewelry, using small faceted pieces of pyrite, often set in [[silver]], has been made since ancient times and was popular in the [[Victorian era]].<ref>{{cite book|last = Hesse|first = Rayner W.|title = Jewelrymaking Through History: An Encyclopedia|publisher = [[Greenwood Publishing Group]]|year = 2007|page = 15|url = https://books.google.com/books?id=IVgU0icm948C&pg=PA15|isbn =978-0-313-33507-5}}</ref> At the time when the term became common in jewelry making, "marcasite" referred to all iron sulfides including pyrite, and not to the orthorhombic FeS<sub>2</sub> mineral [[marcasite]] which is lighter in color, brittle and chemically unstable, and thus not suitable for jewelry making. [[Marcasite jewellery|Marcasite jewelry]] does not actually contain the mineral marcasite. The specimens of pyrite, when it appears as good quality crystals, are used in decoration. They are also very popular in mineral collecting. Among the sites that provide the best specimens are [[Province of Soria|Soria]] and [[La Rioja]] provinces (Spain).<ref>{{Cite journal |last1=Calvo |first1=Miguel |last2=Sevillano |first2=Emilia |date=1989 |title=Pyrite crystals from Soria and La Rioja provinces, Spain |url=https://mineralogicalrecord.com/back_issues/none-50/ |journal=The Mineralogical Record |volume=20 |issue=6 |pages=451–456}}</ref>

In value terms, [[China]] ($47&nbsp;million) constitutes the largest market for imported unroasted iron pyrites worldwide, making up 65% of global imports. China is also the fastest growing in terms of the unroasted iron pyrites imports, with a [[Compound annual growth rate|CAGR]] of +27.8% from 2007 to 2016.<ref>{{Cite web|url=https://www.indexbox.io/blog/which-country-imports-the-most-unroasted-iron-pyrites-in-the-world/|title=Which Country Imports the Most Unroasted Iron Pyrites in the World? – IndexBox|website=www.indexbox.io|access-date=2018-09-11}}</ref>

==Research==
In July 2020 scientists reported that they have observed a voltage-induced transformation of normally [[diamagnetic]] pyrite into a [[ferromagnetic]] material, which may lead to applications in devices such as solar cells or magnetic data storage.<ref>{{cite news |title='Fool's gold' may be valuable after all |url=https://phys.org/news/2020-07-gold-valuable.html |access-date=17 August 2020 |work=phys.org |language=en}}</ref><ref>{{cite journal |last1=Walter |first1=Jeff |last2=Voigt |first2=Bryan |last3=Day-Roberts |first3=Ezra |last4=Heltemes |first4=Kei |last5=Fernandes |first5=Rafael M. |last6=Birol |first6=Turan |last7=Leighton |first7=Chris |title=Voltage-induced ferromagnetism in a diamagnet |journal=Science Advances |date=1 July 2020 |volume=6 |issue=31 |pages=eabb7721 |doi=10.1126/sciadv.abb7721 |pmid=32832693 |pmc=7439324 |bibcode=2020SciA....6.7721W |language=en |issn=2375-2548|doi-access=free }}</ref>

Researchers at [[Trinity College Dublin]], Ireland have demonstrated that FeS<sub>2</sub> can be exfoliated into few-layers just like other two-dimensional layered materials such as graphene by a simple liquid-phase exfoliation route. This is the first study to demonstrate the production of non-layered 2D-platelets from 3D bulk FeS<sub>2</sub>. Furthermore, they have used these 2D-platelets with 20% single walled carbon-nanotube as an anode material in lithium-ion batteries, reaching a capacity of 1000 mAh/g close to the theoretical capacity of FeS<sub>2</sub>.<ref>{{cite journal |last1=Kaur |first1=Harneet |last2=Tian |first2=Ruiyuan |last3=Roy |first3=Ahin |last4=McCrystall |first4=Mark |last5=Horváth |first5=Dominik V. |last6=Onrubia |first6=Guillermo L. |last7=Smith |first7=Ross |last8=Ruether |first8=Manuel |last9=Griffin |first9=Aideen |last10=Backes |first10=Claudia |last11=Nicolosi |first11=Valeria |last12=Coleman |first12=Jonathan N. |title=Production of Quasi-2D Platelets of Non-Layered Iron Pyrite (FeS<sub>2</sub>) by Liquid-Phase Exfoliation for High Performance Battery Electrodes |journal=ACS Nano |date=22 September 2020 |volume=14 |issue=10 |pages=13418–13432 |doi=10.1021/acsnano.0c05292 |pmid=32960568 |url=https://pubs.acs.org/doi/10.1021/acsnano.0c05292|hdl=2262/93605 |s2cid=221864018 |hdl-access=free }}</ref>

In 2021, a natural pyrite stone has been crushed and pre-treated followed by liquid-phase exfoliation into two-dimensional nanosheets, which has shown capacities of 1200 mAh/g as an anode in lithium-ion batteries.<ref>{{cite journal |last1=Kaur |first1=Harneet |last2=Tian |first2=Ruiyuan |last3=Roy |first3=Ahin |last4=McCrystall |first4=Mark |last5=Smith |first5=Ross |last6=Horváth |first6=Dominik V. |last7=Nicolosi |first7=Valeria |last8=Coleman |first8=Jonathan N. |title=2D nanosheets from fool's gold by LPE:High performance lithium-ion battery anodes made from stone |journal=FlatChem |date=November 2021 |volume=30 |issue=10 |pages=13418–13432 |doi=10.1016/j.flatc.2021.100295|hdl=2262/98387 |s2cid=243657098 |hdl-access=free }}</ref>

==Formal oxidation states for pyrite, marcasite, molybdenite and arsenopyrite==

From the perspective of classical [[inorganic chemistry]], which assigns formal oxidation states to each atom, pyrite and marcasite are probably best described as Fe<sup>2+</sup>[S<sub>2</sub>]<sup>2−</sup>. This formalism recognizes that the sulfur atoms in pyrite occur in pairs with clear S–S bonds. These [[Disulfide|persulfide]] [<sup>–</sup>S–S<sup>–</sup>] units can be viewed as derived from [[hydrogen disulfide]], H<sub>2</sub>S<sub>2</sub>. Thus pyrite would be more descriptively called iron persulfide, not iron disulfide. In contrast, [[molybdenite]], [[molybdenum|Mo]]S<sub>2</sub>, features isolated sulfide S<sup>2−</sup> centers and the oxidation state of molybdenum is Mo<sup>4+</sup>. The mineral [[arsenopyrite]] has the formula Fe[[arsenic|As]]S. Whereas pyrite has [S<sub>2</sub>]<sup>2–</sup> units, arsenopyrite has [AsS]<sup>3–</sup> units, formally derived from [[deprotonation]] of arsenothiol (H<sub>2</sub>AsSH). Analysis of classical oxidation states would recommend the description of arsenopyrite as Fe<sup>3+</sup>[AsS]<sup>3−</sup>.<ref name=Vaughan>{{cite book |author1=Vaughan, D. J. |author2=Craig, J. R. |title=Mineral Chemistry of Metal Sulfides |publisher=Cambridge University Press |location=Cambridge, UK |year=1978 |isbn=978-0-521-21489-6}}</ref>

==Crystallography==
[[Image:FeS2structure.png|thumb|right|Crystal structure of pyrite. In the center of the cell a S<sub>2</sub><sup>2−</sup> pair is seen in yellow.]]

Iron-pyrite FeS<sub>2</sub> represents the prototype compound of the [[Crystallography|crystallographic]] pyrite structure. The structure is [[cubic crystal system|cubic]] and was among the first [[crystal structures]] solved by [[X-ray diffraction]].<ref name=Brag1913>{{cite journal|author=Bragg, W. L.|title=The structure of some crystals as indicated by their diffraction of X-rays|journal=[[Proceedings of the Royal Society A]]|volume=89|pages=248–277|year=1913|doi=10.1098/rspa.1913.0083|bibcode=1913RSPSA..89..248B|issue=610|jstor=93488|doi-access=free}}</ref> It belongs to the crystallographic [[space group]] ''Pa''{{overline|3}} and is denoted by the [[Zeitschrift für Kristallographie|Strukturbericht]] notation C2. Under thermodynamic standard conditions the [[lattice constant]] <math>a</math> of stoichiometric iron pyrite FeS<sub>2</sub> amounts to {{nowrap|541.87 pm}}.<ref name=Birk1991>{{cite journal|title=Sulfur deficiency in iron pyrite (FeS<sub>2−x</sub>) and its consequences for band structure models|journal=Physical Review B|volume=43|pages=11926–11936|year=1991|doi=10.1103/PhysRevB.43.11926|bibcode=1991PhRvB..4311926B|issue=14|last1=Birkholz|first1=M.|last2=Fiechter|first2=S.|last3=Hartmann|first3=A.|last4=Tributsch|first4=H.|pmid=9996968}}</ref> The [[cubic crystal system#Voids in the unit cell|unit cell]] is composed of a Fe [[Bravais lattice|face-centered cubic sublattice]] into which the {{chem|S|2}} ions are embedded. (Note though that the iron atoms in the faces are not equivalent by translation alone to the iron atoms at the corners.) The pyrite structure is also seen in other ''MX''<sub>2</sub> compounds of [[transition metals]] ''M'' and [[chalcogen]]s ''X'' = [[oxygen|O]], [[sulfur|S]], [[selenium|Se]] and [[tellurium|Te]]. Certain [[pnictide|dipnictides]] with ''X'' standing for [[phosphorus|P]], [[arsenic|As]] and [[antimony|Sb]] etc. are also known to adopt the pyrite structure.<ref name=Bres1994>{{cite journal|title=Bonding Trends in Pyrites and a Reinvestigation of the Structure of PdAs<sub>2</sub>, PdSb<sub>2</sub>, PtSb<sub>2</sub> and PtBi<sub>2</sub>|journal=Z. Anorg. Allg. Chem.|volume=620|issue=3|pages=393–404|year=1994|doi=10.1002/zaac.19946200302|last1=Brese|first1=Nathaniel E.|last2=von Schnering|first2=Hans Georg}}</ref>

The Fe atoms are bonded to six S atoms, giving a distorted octahedron. The material is a [[semiconductor]]. The Fe ions are usually considered to be ''[[low spin]]'' [[divalent]] state (as shown by [[Mössbauer spectroscopy]] as well as XPS). The material as a whole behaves as a Van Vleck [[Paramagnetism|paramagnet]], despite its low-spin divalency.<ref>{{Cite journal|last1=Burgardt|first1=P.|last2=Seehra|first2=M. S.|date=1977-04-01|title=Magnetic susceptibility of iron pyrite (FeS2) between 4.2 and 620 K|journal=Solid State Communications|volume=22|issue=2|pages=153–156|doi=10.1016/0038-1098(77)90422-7|bibcode=1977SSCom..22..153B|issn=0038-1098}}</ref>

The sulfur centers occur in pairs, described as S<sub>2</sub><sup>2−</sup>.<ref>{{cite journal|last1=Hulliger|first1=F.|title=Electrical Properties of Pyrite-Type and Related Compounds with Zero Spin Moment|journal=Nature|date=December 1963|volume=200|issue=4911|pages=1064–1065|doi=10.1038/2001064a0|bibcode=1963Natur.200.1064H|s2cid=32504249}}</ref><!-- Really need a more recent source--> Reduction of pyrite with potassium gives [[potassium dithioferrate]], KFeS<sub>2</sub>. This material features ferric ions and isolated sulfide (S<sup>2-</sup>) centers.

The S atoms are tetrahedral, being bonded to three Fe centers and one other S atom. The site symmetry at Fe and S positions is accounted for by [[crystallographic point group|point symmetry groups]] ''C''<sub>3''i''</sub> and ''C''<sub>3</sub>, respectively. The missing [[centrosymmetry|center of inversion]] at S lattice sites has important consequences for the crystallographic and physical properties of iron pyrite. These consequences derive from the crystal electric field active at the sulfur lattice site, which causes a [[Chemical polarity|polarization]] of S ions in the pyrite lattice.<ref name=BJPC1992>{{cite journal|author=Birkholz, M.|url=https://www.researchgate.net/publication/231101585|title=The crystal energy of pyrite|journal=J. Phys.: Condens. Matter|volume=4|pages=6227–6240|year=1992|doi=10.1088/0953-8984/4/29/007|bibcode=1992JPCM....4.6227B|issue=29|s2cid = 250815717 }}</ref> The polarisation can be calculated on the basis of higher-order [[Madelung constant]]s and has to be included in the calculation of the [[lattice energy]] by using a generalised [[Born–Haber cycle]]. This reflects the fact that the covalent bond in the sulfur pair is inadequately accounted for by a strictly ionic treatment.<ref>{{cite journal|last1=Wood|first1=Robert|title=Madelung Constants for the Calcium Carbide and Pyrite Crystal Structures|journal=The Journal of Chemical Physics|date=August 1962|volume=37|issue=3|pages=598–600|doi=10.1063/1.1701381|bibcode=1962JChPh..37..598W }}</ref>

Arsenopyrite has a related structure with heteroatomic As–S pairs rather than S-S pairs. Marcasite also possesses homoatomic anion pairs, but the arrangement of the metal and diatomic anions differs from that of pyrite. Despite its name, chalcopyrite ({{chem|CuFeS|2}}) does not contain dianion pairs, but single S<sup>2−</sup> sulfide anions.

==Crystal habit==
[[File:Pyrite elbe.jpg|thumb|right|[[Pyritohedron]]-shaped crystals from Italy]]
Pyrite usually forms cuboid crystals, sometimes forming in close association to form raspberry-shaped masses called [[framboid]]s. However, under certain circumstances, it can form [[Anastomosis|anastomosing]] filaments or T-shaped crystals.<ref name="Bonev2005">{{Cite journal | last1 = Bonev | first1 = I. K. | last2 = Garcia-Ruiz | first2 = J. M. | last3 = Atanassova | first3 = R. | last4 = Otalora | first4 = F. | last5 = Petrussenko | first5 = S. | title = Genesis of filamentary pyrite associated with calcite crystals | doi = 10.1127/0935-1221/2005/0017-0905 | journal = European Journal of Mineralogy | volume = 17 | issue = 6 | pages = 905–913 | year = 2005 | citeseerx = 10.1.1.378.3304 | bibcode = 2005EJMin..17..905B }}</ref>
Pyrite can also form shapes almost the same as a regular [[dodecahedron]], known as pyritohedra, and this suggests an explanation for the artificial geometrical models found in Europe as early as the 5th century BC.<ref>The pyritohedral form is described as a dodecahedron with [[pyritohedral symmetry]]; Dana J. et al., (1944), ''System of mineralogy'', New York, p 282</ref>{{clarify|date=December 2019}}

==Varieties==
[[Cattierite]] ([[Cobalt|Co]][[sulfur|S]]<sub>2</sub>), [[vaesite]] ([[Nickel|Ni]][[sulfur|S]]<sub>2</sub>) and [[hauerite]] ([[Manganese|Mn]][[sulfur|S]]<sub>2</sub>), as well as [[sperrylite]] ([[Platinum|Pt]][[arsenic|As]]<sub>2</sub>) are similar in their structure and belong also to the pyrite group.

'''{{vanchor|Bravoite}}''' is a nickel-cobalt bearing variety of pyrite, with >&nbsp;50% substitution of [[nickel|Ni]]<sup>2+</sup> for Fe<sup>2+</sup> within pyrite. Bravoite is not a formally recognised mineral, and is named after the Peruvian scientist Jose J. Bravo (1874–1928).<ref>[http://www.mindat.org/min-759.html Mindat&nbsp;– bravoite]. Mindat.org (2011-05-18). Retrieved on 2011-05-25.</ref>

==Distinguishing similar minerals==
Pyrite is distinguishable from [[Gold#Occurrence|native gold]] by its hardness, brittleness and crystal form. Pyrite fractures are very [[Fracture (mineralogy)#Uneven fracture|uneven]], sometimes [[conchoidal fracture|conchoidal]] because it does not cleave along a preferential plane. Native [[gold nugget]]s, or glitters, do not break but deform in a [[ductility|ductile]] way. Pyrite is brittle, gold is malleable.

Natural gold tends to be [[Euhedral and anhedral|anhedral]] (irregularly shaped without well defined faces), whereas pyrite comes as either cubes or multifaceted crystals with well developed and sharp faces easy to recognise. Well crystallised pyrite crystals are [[euhedral]] (''i.e.'', with nice faces). Pyrite can often be distinguished by the striations which, in many cases, can be seen on its surface. [[Chalcopyrite]] ({{Chem2|CuFeS2}}) is brighter yellow with a greenish hue when wet and is softer (3.5–4 on Mohs' scale).<ref>[http://www.minerals.net/mineral/sulfides/pyrite/pyrite.htm Pyrite on]. Minerals.net (2011-02-23). Retrieved on 2011-05-25.</ref> [[Arsenopyrite]] (FeAsS) is silver white and does not become more yellow when wet.

==Hazards==
[[File:GoldinPyriteDrainage acide.JPG|thumb|A pyrite cube (center) has dissolved away from a host rock, leaving behind trace gold]]
Iron pyrite is unstable when exposed to the [[redox|oxidizing]] conditions prevailing at the Earth's surface: iron pyrite in contact with atmospheric [[oxygen]] and water, or damp, ultimately decomposes into [[iron oxides|iron oxyhydroxides]] ([[ferrihydrite]], FeO(OH)) and [[sulfuric acid]] ({{chem|H|2|S|O|4}}). This process is accelerated by the action of ''[[Acidithiobacillus]]'' bacteria which oxidize pyrite to first produce [[ferrous ion]]s ({{chem|Fe|2+}}), [[sulfate]] ions ({{chem|SO|4|2-}}), and release protons ({{H+}}, or {{H3O+}}). In a second step, the ferrous ions ({{chem|Fe|2+}}) are oxidized by {{O2}} into [[ferric ion]]s ({{chem|Fe|3+}}) which [[hydrolysis|hydrolyze]] also releasing {{H+}} ions and producing FeO(OH). These oxidation reactions occur more rapidly when pyrite is finely dispersed (framboidal crystals initially formed by [[Sulfate-reducing microorganisms|sulfate reducing bacteria]] (SRB) in argillaceous sediments or dust from mining operations).

===Pyrite oxidation and acid mine drainage===
{{Main article|Acid mine drainage}}
Pyrite oxidation by atmospheric {{O2}} in the presence of moisture ({{H2O}}) initially produces ferrous ions ({{chem|Fe|2+}}) and [[sulfuric acid]] which dissociates into [[sulfate]] ions and [[hydronium|protons]], leading to [[acid mine drainage]] (AMD). An example of acid rock drainage caused by pyrite is the [[2015 Gold King Mine waste water spill]].<ref>{{cite web| url = http://www.westech-inc.com/en-usa/industry-solutions/mineral-overview/acid-mine-drainage| title = Acid Mine Drainage}}</ref>

:{{chem2 | 2 FeS2 (s) + 7 O2 (g) + 2 H2O (l) -> 2 Fe(2+) (aq) + 4 SO4(2-) (aq) + 4 H+ (aq) }}

===Dust explosions===
Pyrite oxidation is sufficiently [[exothermic]] that underground [[coal mine]]s in high-sulfur coal seams have occasionally had serious problems with [[spontaneous combustion]].<ref>{{cite journal |last1=Deng |first1=Jun |last2=Ma |first2=Xiaofeng |last3=Zhang |first3=Yutao |last4=Li |first4=Yaqing |last5=Zhu |first5=Wenwen |title=Effects of pyrite on the spontaneous combustion of coal |journal=International Journal of Coal Science & Technology |date=December 2015 |volume=2 |issue=4 |pages=306–311 |doi=10.1007/s40789-015-0085-y|doi-access=free |bibcode=2015IJCST...2..306D }}</ref> The solution is the use of buffer blasting and the use of various sealing or cladding agents to [[Hermetic seal|hermetically seal]] the mined-out areas to exclude oxygen.<ref>{{cite journal |last1=Onifade |first1=Moshood |last2=Genc |first2=Bekir |title=A review of spontaneous combustion studies – South African context |journal=International Journal of Mining, Reclamation and Environment |date=17 November 2019 |volume=33 |issue=8 |pages=527–547 |doi=10.1080/17480930.2018.1466402|bibcode=2019IJMRE..33..527O |s2cid=116125498 }}</ref>

In modern coal mines, [[limestone]] dust is sprayed onto the exposed coal surfaces to reduce the hazard of [[dust explosion]]s. This has the secondary benefit of neutralizing the acid released by pyrite oxidation and therefore slowing the oxidation cycle described above, thus reducing the likelihood of spontaneous combustion. In the long term, however, oxidation continues, and the [[hydrated]] [[sulfate]]s formed may exert crystallization pressure that can expand cracks in the rock and lead eventually to [[cave-in|roof fall]].<ref>{{cite journal |doi=10.1016/j.coal.2005.03.013 |title=Colliery and surface hazards through coal-pyrite oxidation (Pennsylvanian Sydney Coalfield, Nova Scotia, Canada) |year=2005 |last1=Zodrow |first1=E |journal=International Journal of Coal Geology |volume=64 |issue=1–2 |pages=145–155|bibcode=2005IJCG...64..145Z }}</ref>

===Weakened building materials===
{{Main article|Concrete degradation|Sulfate attack in concrete and mortar}}
Building stone containing pyrite tends to stain brown as pyrite oxidizes. This problem appears to be significantly worse if any [[marcasite]] is present.<ref>Bowles, Oliver (1918) [https://books.google.com/books?id=OksMAAAAYAAJ&lpg=PA25&pg=PA25 The structural and ornamental stones of Minnesota]. Bulletin 663, United States Geological Survey, Washington. p. 25.</ref> The presence of pyrite in the [[Construction aggregate|aggregate]] used to make [[concrete]] can lead to severe deterioration as pyrite oxidizes.<ref>{{cite journal|doi=10.1016/j.cemconres.2004.06.030|title=Internal deterioration of concrete by the oxidation of pyrrhotitic aggregates|year=2005 |last1=Tagnithamou|first1=A|last2=Sariccoric|first2=M |last3=Rivard|first3=P |journal=Cement and Concrete Research|volume=35|pages=99–107}}</ref> In early 2009, problems with [[Chinese drywall]] imported into the [[United States]] after [[Hurricane Katrina]] were attributed to pyrite oxidation, followed by microbial sulfate reduction which released [[hydrogen sulfide]] gas ({{H2S}}). These problems included a foul odor and [[corrosion]] of [[copper]] wiring.<ref>Angelo, William (28 January 2009) [http://www.enr.com/articles/2472-a-material-odor-mystery-over-foul-smelling-drywall A material odor mystery over foul-smelling drywall]. Engineering News-Record.</ref> In the United States, in Canada,<ref>"[https://acqc.ca/sites/default/files/pdf/pyrihouse.pdf Pyrite and your house, what home-owners should know] {{webarchive|url=https://web.archive.org/web/20120106014634/http://www.consommateur.qc.ca/acqc/PyriHouse.pdf |date=2012-01-06 }}" – {{ISBN|2-922677-01-X}} – Legal deposit – National Library of Canada, May 2000</ref> and more recently in Ireland,<ref>Shrimer, F. and Bromley, AV (2012) "Pyritic Heave in Ireland". ''Proceedings of the Euroseminar on Building Materials''. International Cement Microscopy Association (Halle Germany)</ref><ref>[http://www.irishtimes.com/newspaper/ireland/2011/0611/1224298735366.html Homeowners in protest over pyrite damage to houses]. The Irish Times (11 June 2011</ref><ref>Brennan, Michael (22 February 2010) [http://www.independent.ie/irish-news/devastating-pyrite-epidemic-hits-20000-newly-built-houses-26634603.html Devastating 'pyrite epidemic' hits 20,000 newly built houses]. ''Irish Independent''</ref> where it was used as underfloor infill, pyrite contamination has caused major structural damage. [[Concrete]] exposed to sulfate ions, or sulfuric acid, degrades by [[sulfate attack]]: the formation of expansive mineral phases, such as [[ettringite]] (small needle crystals exerting a huge crystallization pressure inside the concrete pores) and [[gypsum]] creates inner [[tensile force]]s in the concrete matrix which destroy the hardened [[cement]] paste, form cracks and fissures in concrete, and can lead to the ultimate ruin of the structure. Normalized tests for [[construction aggregate]]<ref>I.S. EN 13242:2002 [https://www.roadstone.ie/revision-s-r-21/ Aggregates for unbound and hydraulically bound materials for use in civil engineering work and road construction] {{Webarchive|url=https://web.archive.org/web/20180802162539/https://www.roadstone.ie/revision-s-r-21/ |date=2018-08-02 }}</ref> certify such materials as free of pyrite or marcasite.

==Occurrence==
Pyrite is the most common of sulfide minerals and is widespread in igneous, metamorphic, and sedimentary rocks. It is a common accessory mineral in igneous rocks, where it also occasionally occurs as larger masses arising from an [[Miscibility|immiscible]] sulfide phase in the original magma. It is found in metamorphic rocks as a product of [[contact metamorphism]]. It also forms as a high-temperature [[hydrothermal mineralization|hydrothermal mineral]], though it occasionally forms at lower temperatures.<ref name="Hurlbut"/>
 
Pyrite occurs both as a primary mineral, present in the original sediments, and as a secondary mineral, deposited during [[diagenesis]].<ref name="Hurlbut"/> Pyrite and [[marcasite]] commonly occur as replacement [[pseudomorph]]s after [[fossils]] in [[black shale]] and other [[sedimentary rocks]] formed under [[Redox|reducing]] environmental conditions.<ref>{{Cite journal|last1=Briggs|first1=D. E. G.|last2=Raiswell|first2=R.|last3=Bottrell|first3=S. H.|last4=Hatfield|first4=D.|last5=Bartels|first5=C.|date=1996-06-01|title=Controls on the pyritization of exceptionally preserved fossils; an analysis of the Lower Devonian Hunsrueck Slate of Germany|journal=American Journal of Science|language=en|volume=296|issue=6|pages=633–663|doi=10.2475/ajs.296.6.633|issn=0002-9599|bibcode=1996AmJS..296..633B}}</ref> Pyrite is common as an accessory mineral in shale, where it is formed by precipitation from anoxic seawater, and coal beds often contain significant pyrite.<ref>{{cite book |last1=Nesse |first1=William D. |title=Introduction to mineralogy |date=2000 |publisher=Oxford University Press |location=New York |isbn=9780195106916 |page=390}}</ref>

Notable deposits are found as lenticular masses in Virginia, U.S., and in smaller quantities in many other locations. Large deposits are mined at Rio Tinto in Spain and elsewhere in the Iberian Peninsula.<ref>{{Cite journal |last=J.M. Leistel, E. Marcoux , D. Thiéblemont , C. Quesada, A. Sánchez, G.R. Almodóvar, E. Pascualand R. Sáez |title=The volcanic-hosted massive sulphide deposits of the Iberian Pyrite Belt |journal=Mineralium Deposita |date=1997 |volume=33 |issue=1–2 |pages=2–30|doi=10.1007/s001260050130 |bibcode=1997MinDe..33....2L }}</ref>

==Cultural beliefs==
In the beliefs of the Thai people (especially those in the south), pyrite is known as ''Khao tok [[Phra Ruang]]'', ''Khao khon bat Phra Ruang'' (ข้าวตอกพระร่วง, ข้าวก้นบาตรพระร่วง) or ''Phet na tang'', ''Hin na tang'' (เพชรหน้าทั่ง, หินหน้าทั่ง). It is believed to be a [[amulet|sacred item]] that has the power to prevent evil, [[black magic]] or demons.<ref>{{cite web|url=https://www.dailynews.co.th/regional/736100/|title=ไขข้อข้องใจ'เพชรหน้าทั่ง' สรรพคุณรองจาก'เหล็กไหล'|date=2019-10-11|accessdate=2021-08-26|work=Daily News|language=thai|trans-title=Solve the question of 'Phet na tang', secondary properties after 'Lek Lai'}}</ref><ref>{{cite web|url=https://www.komchadluek.net/news/local/458649|work=Komchadluek|language=Thai|date=2021-02-17|accessdate=2021-08-26|title=ของดีหายาก "ข้าวตอกพระร่วง-ข้าวก้นบาตรพระร่วง" หินศักดิ์สิทธิ์แห่งกรุงสุโขทัย|trans-title=A rare good item "Khao tok Phra Ruang - Khao khon bat Phra Ruang", a sacred stone of Sukhothai kingdom}}</ref>

==Images==
<gallery widths="133px" heights="130px">
File:Bullypyrite2.jpg|As a [[Fossil#Replacement and recrystallization|replacement mineral]] in an [[ammonite]] from France
File:Pyrite from Ampliación a Victoria Mine, Navajún, La Rioja, Spain 2.jpg|Pyrite from Ampliación a Victoria Mine, Navajún, La Rioja, Spain
File:Pyrite-Tetrahedrite-Quartz-184642.jpg|Pyrite from the [[Sweet Home Mine]], with golden striated cubes intergrown with minor tetrahedrite, on a bed of transparent quartz needles
File:Pyrite-200582.jpg|Radiating form of pyrite
File:Paraspirifer bownockeri.fond.jpg|''[[Paraspirifer|Paraspirifer bownockeri]]'' in pyrite
File:Fluorite-Pyrite-tmu38b.jpg|Pink fluorite perched between pyrite on one side and metallic galena on the other side
File:Pyrite in pyrrhotite SEM image.png|SEM image of intergrowth of pyrite cuboctahedral crystals (yellow) and pyrrhotite (pinkish yellow)
</gallery>

==See also==
* [[Iron–sulfur world hypothesis]]
* [[Sulfur isotope biogeochemistry]]

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

==Further reading==
* American Geological Institute, 2003, ''Dictionary of Mining, Mineral, and Related Terms'', 2nd ed., Springer, New York, {{ISBN|978-3-540-01271-9}}.
* David Rickard, ''Pyrite: A Natural History of Fool's Gold'', Oxford, New York, 2015, {{ISBN|978-0-19-020367-2}}.

==External links==

{{Commons category|Pyrite}}
* [http://museomine.unizar.es/pirita  Pyrite.Virtual Museum of Mineralogy. Universidad de Zaragoza, Spain]
* [https://web.archive.org/web/20150618122745/http://www.spanishminerals.com/blog/?p=31 Educational article about the famous pyrite crystals from the Navajun Mine]
* [https://web.archive.org/web/20061124083320/http://www.geo.uw.edu.pl/ZASOBY/PYRITE/pyrite6.htm How Minerals Form and Change] "Pyrite oxidation under room conditions".
* {{cite web|last=Poliakoff|first=Martyn|title=Fool's Gold|url=http://www.periodicvideos.com/videos/feature_fools_gold.htm|work=[[The Periodic Table of Videos]]|publisher=[[University of Nottingham]]|author-link=Martyn Poliakoff|year=2009}}

{{sulfur compounds}}
{{Disulfides}}
{{Authority control}}

[[Category:Disulfides]]
[[Category:Fire making]]
[[Category:Pyrite group]]
[[Category:Iron(II) minerals]]
[[Category:Cubic minerals]]
[[Category:Minerals in space group 205]]
[[Category:Sulfide minerals]]
[[Category:Alchemical substances]]
[[Category:Semiconductor materials]]
[[Category:Transition metal dichalcogenides]]
[[Category:Blendes]]