# Greigite

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> Source: https://en.wikipedia.org/wiki/Greigite
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{{short description|Iron sulfide mineral of spinel structure}}
{{Infobox mineral
| name        = Greigite
| image       = Greigite structure 110 SFe4 tetrahedra.png
| alt         = 
| caption     = Greigite structure, SFe<sub>4</sub> tetrahedra
| category    = [Sulfide mineral](/source/Sulfide_mineral) <br />[Thiospinel group](/source/Thiospinel_group) <br />Spinel structural group
| formula     = {{chem2|Fe^{2+}Fe^{3+}2S4}}
| IMAsymbol   = Grg<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   = 
| strunz      = 2.DA.05
| dana        = 
| system      = [Cubic](/source/Cubic_crystal_system)
| class       = Hexoctahedral (m{{overline|3}}m) <br/>[H-M symbol](/source/H-M_symbol): (4/m {{overline|3}} 2/m)
| symmetry    = ''F''d{{overline|3}}m
| unit cell   = a = 9.876&nbsp;Å; Z&nbsp;=&nbsp;8
| color       = Pale pink, tarnishes to metallic blue-black
| colour      = 
| habit       = Spheres of intergrown octahedra and as disseminated microscopic grains
| twinning    = 
| cleavage    = 
| fracture    = 
| tenacity    = 
| mohs        = 4 to 4.5
| luster      = Metallic to earthy
| streak      = 
| diaphaneity = Opaque
| gravity     = 4.049
| density     = 
| polish      = 
| opticalprop = 
| refractive  = 
| birefringence = 
| pleochroism = 
| 2V          = 
| dispersion  = 
| extinction  = 
| length fast/slow =
| fluorescence = 
| absorption  = 
| melt        = 
| fusibility  = 
| diagnostic  = 
| solubility  = 
| impurities  = 
| alteration  = 
| other       = Strongly magnetic
| prop1       = 
| prop1text   = 
| references  = <ref name=Handbook>{{cite book|editor1=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, VA, US|chapter-url=http://rruff.geo.arizona.edu/doclib/hom/greigite.pdf |chapter=Greigite |access-date=December 5, 2011|isbn=0-9622097-0-8
|volume=I (Elements, Sulfides, Sulfosalts)|year=1990}}</ref><ref name=Mindat>[http://www.mindat.org/min-1747.html Greigite]. Mindat.org</ref><ref name=Webmin>[http://webmineral.com/data/Greigite.shtml Greigite]. Webmineral</ref>
}}
'''Greigite''' is an [iron](/source/iron) [sulfide](/source/sulfide) mineral with the chemical formula {{chem2|Fe^{2+}Fe^{3+}2S4}}. It is the sulfur equivalent of the iron oxide [magnetite](/source/magnetite) (Fe<sub>3</sub>O<sub>4</sub>). It was first described in 1964 for an occurrence in [San Bernardino County, California](/source/San_Bernardino_County%2C_California), and named after the mineralogist and physical chemist [Joseph W. Greig](/source/Joseph_W._Greig) (1895–1977).<ref name=Webmin/><ref>{{cite journal | url =  http://www.minsocam.org/ammin/AM49/AM49_543.pdf | title = Greigite, the thio-spinel of iron; a new mineral | journal = American Mineralogist |first1 = Brian J. | last1 = Skinner | first2 = Richard C. | last2= Erd | first3 = Frank S. | last3 = Grimaldi | pages = 543–55 | volume = 49 | year = 1964}}</ref>

==Natural occurrence and composition==
{{See also|Iron-sulfur protein}}
It occurs in [lacustrine](/source/Lake) sediments with [clays](/source/Clay_mineral), [silt](/source/silt)s and [arkosic sand](/source/Arkose) often in [varve](/source/varve)d [sulfide](/source/sulfide) rich clays. It is also found in [hydrothermal](/source/hydrothermal) [veins](/source/Vein_(geology)).  Greigite is formed by [magnetotactic bacteria](/source/magnetotactic_bacteria) and sulfate-reducing bacteria.<ref name=Handbook/> Greigite has also been identified in the [sclerite](/source/sclerite)s of [scaly-foot gastropod](/source/scaly-foot_gastropod)s.<ref>{{Cite web|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|archive-date=November 10, 2003|title=Armor-Plated Snail Discovered in Deep Sea|website=news.nationalgeographic.com|access-date=2016-08-29}}</ref> 
  
The mineral typically appears as microscopic (< 0.03&nbsp;mm) isometric hexoctahedral crystals and as minute sooty masses. Association minerals include [montmorillonite](/source/montmorillonite), [chlorite](/source/Chlorite_group), [calcite](/source/calcite), [colemanite](/source/colemanite), [veatchite](/source/veatchite), [sphalerite](/source/sphalerite), [pyrite](/source/pyrite), [marcasite](/source/marcasite), [galena](/source/galena) and [dolomite](/source/dolomite_(mineral)).<ref name=Handbook/><ref name=Mindat/>

Common impurities include Cu, Ni, Zn, Mn, Cr, Sb and As.<ref name=Mindat/> Ni impurities are of particular interest because the structural similarity between Ni-doped greigite and the [{{chem2|(Fe,Ni)S}} clusters](/source/Iron%E2%80%93nickel_clusters) present in biological enzymes has led to suggestions that greigite or similar minerals could have acted as catalysts for the [origin of life](/source/origin_of_life).<ref name="RussellMartin2004">{{cite journal|last1=Russell|first1=Michael J.|last2=Martin|first2=William|title=The rocky roots of the acetyl-CoA pathway|journal=Trends in Biochemical Sciences|volume=29|issue=7|year=2004|pages=358–363|issn=0968-0004|doi=10.1016/j.tibs.2004.05.007|pmid=15236743}}</ref> In particular, the cubic Fe<sub>4</sub>S<sub>4</sub> unit of greigite is found in the Fe<sub>4</sub>S<sub>4</sub> thiocubane units of proteins of relevance to the [acetyl-CoA](/source/acetyl-CoA) pathway.

==Crystal structure==
Greigite has the [spinel](/source/spinel) structure. The crystallographic unit cell is cubic, with [space group](/source/space_group) Fd3m. The S anions form a cubic close-packed lattice, and the Fe cations occupy both tetrahedral and octahedral sites.<ref name=Handbook/><ref name=Vaughan>Vaughan, D. J.; Craig, J. R. "Mineral Chemistry of Metal Sulfides" Cambridge University Press, Cambridge: 1978. {{ISBN|0-521-21489-0}}.</ref>

==Magnetic and electronic properties==
Like the related oxide [magnetite](/source/magnetite) (Fe<sub>3</sub>O<sub>4</sub>), greigite is [ferrimagnetic](/source/ferrimagnetic), with the spin magnetic moments of the Fe cations in the tetrahedral sites oriented in the opposite direction as those in the octahedral sites, and a net magnetization.  It is a [mixed-valence compound](/source/mixed-valence_compound), featuring both Fe(II) and Fe(III) centers in a 1:2 ratio. Both metal sites have high [spin quantum number](/source/spin_quantum_number)s. The electronic structure of greigite is that of a [half metal](/source/half_metal).<ref name=devey09>{{cite journal|last1=Devey|first1=A.J.|last2=Grau-Crespo|first2=R.|last3=Leeuw|first3=N.H.|title=Electronic and magnetic structure of Fe<sub>3</sub>S<sub>4</sub>: GGA+U investigation|journal=Physical Review B|year=2009|volume=79|article-number=195126| doi=10.1103/PhysRevB.79.195126|issue=19|bibcode = 2009PhRvB..79s5126D }}</ref><ref>{{cite journal| title=The Curie temperature and magnetic exchange energy in half-metallic greigite Fe<sub>3</sub>S<sub>4</sub>|doi=10.1088/0031-8949/83/04/045702|year=2011|volume=83|article-number=045702| last1=Wang| first1=Jun| last2=Cao| first2=Shi-He| last3=Wu| first3=Wei| last4=Zhao| first4=Guo-Meng| journal=Physica Scripta| issue=4|bibcode = 2011PhyS...83d5702W |s2cid=121375069 }}</ref>

== On Mars ==
A September 10, 2025 paper published in ''[Nature](/source/Nature_(journal))'' reported the "likely" detection of greigite and [vivianite](/source/vivianite) in the [Jezero crater](/source/Jezero_(crater)) on [Mars](/source/Mars), by the ''[Perseverance](/source/Perseverance_(rover))'' rover.<ref name="Nature2025"/> It is considered a potential [biosignature](/source/biosignature).<ref name="NASA2025"/>

==References==
{{Reflist| refs=

<ref name="Nature2025">{{cite journal |last1=Hurowitz |first1=J. A. |last2=Tice |first2=M. M. |last3=Allwood |first3=A. C. |title=Redox-driven mineral and organic associations in Jezero Crater, Mars |journal=Nature |date=11 September 2025 |volume=645 |pages=332–340 |doi=10.1038/s41586-025-09413-0 |doi-access=free }}</ref>

<ref name="NASA2025">{{cite web |last1=Taveau |first1=Jessica |title=NASA Says Mars Rover Discovered Potential Biosignature Last Year |url=https://www.nasa.gov/news-release/nasa-says-mars-rover-discovered-potential-biosignature-last-year/ |website=nasa.gov |publisher=NASA|date=2025-09-10}}</ref>

}}

Category:Thiospinel group
Category:Iron(II,III) minerals
Category:Ferromagnetic materials
Category:Magnetic minerals
Category:Cubic minerals
Category:Minerals in space group 227

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Adapted from the Wikipedia article [Greigite](https://en.wikipedia.org/wiki/Greigite) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Greigite?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.