{{Short description|Rare mineral primarily made of copper and aluminum}} {{Infobox mineral | name = Khatyrkite | category = Native element class, alloy | boxwidth = | image = Khatyrkite sample.png | caption = Khatyrkite sample. | formula = {{chem2|(Cu,Zn,Fe)Al2}} | IMAsymbol = Ktk<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> | strunz = 1.AA.15 | system = Tetragonal | class = Ditetragonal dipyramidal (4/mmm) <br/>H-M symbol: (4/m 2/m 2/m) | symmetry = ''I4/mcm'' | unit cell = a = 6.06, c = 4.87&nbsp;[Å]; Z&nbsp;=&nbsp;4 | color = Gray-yellow (reflection) | habit = Prismatic crystals and intergrowths with cupalite | twinning = | cleavage = {100}, distinct | tenacity = Malleable | mohs = 5–6 | luster = Metallic | diaphaneity = Opaque | opticalprop = Distinctly anisotropic, grayish yellow to brownish red | refractive = | birefringence = | streak = Dark gray | gravity = 4.42 (calculated) | melt = | fusibility = | solubility = | other = | references =<ref name = handbook>{{cite web|url=https://www.handbookofmineralogy.org/pdfs/khatyrkite.pdf|title=Khatyrkite|publisher=Mineral Data Publishing|access-date=2009-08-07}}</ref><ref name=mindat>{{cite web|url=http://www.mindat.org/min-2197.html|title=Khatyrkite|publisher=Mindat.org|access-date=2010-08-07}}</ref><ref name=webmin>{{cite web|url=https://webmineral.com/data/Khatyrkite.shtml|title=Khatyrkite|publisher=Webmineral|access-date=2010-08-07}}</ref> }}

'''Khatyrkite''' ({{IPAc-en|ˈ|k|æ|t|i|ər|k|aɪ|t}} {{respell|KAT|ee|ər|kyte}})<ref>[https://webmineral.com/data/Khatyrkite.shtml Khatyrkite Mineral Data]</ref> is a rare mineral which is mostly composed of copper and aluminium, but may contain up to about 15% of zinc or iron.<ref name=webmin/><ref name=j1>{{cite journal|last1=Steinhardt|first1=Paul|last2=Bindi|first2=Luca|title=Once upon a time in Kamchatka: the search for natural quasicrystals|doi=10.1080/14786435.2010.510457|year=2010|pages=1|journal=Philosophical Magazine|volume=91|issue=19–21|url=http://www.physics.princeton.edu/~steinh/naturalquasicrystals.html|bibcode=2011PMag...91.2421S|citeseerx=10.1.1.670.9567|s2cid=120117070|archive-date=2011-09-27|access-date=2010-12-29|archive-url=https://web.archive.org/web/20110927094940/http://www.physics.princeton.edu/~steinh/naturalquasicrystals.html|url-status=dead}}</ref> Its chemical structure is described by an approximate formula {{chem2|(Cu,Zn)Al2}} or {{chem|(Cu,Fe)Al2}}. It was discovered in 1985 in a placer in association with another rare mineral cupalite ({{chem2|(Cu,Zn,Fe)Al}}). These two minerals have only been found at {{coord|62|39|11|N|174|30|02|E|}} in the area of the Iomrautvaam, a tributary of the Khatyrka river, in the Koryak Mountains, in Anadyrsky District (former Beringovsky District), Chukotka, Russia. Analysis of one of the samples containing khatyrkite showed that the small rock was from a meteorite.<ref name=Bindi2011>{{Cite journal| doi = 10.1073/pnas.1111115109| pmid = 22215583| last = Bindi| first = Luca|author2=John M. Eiler |author3=Yunbin Guan |author4=Lincoln S. Hollister|author5=Glenn MacPherson |author6=Paul J. Steinhardt |author7=Nan Yao| title = Evidence for the extraterrestrial origin of a natural quasicrystal| journal = Proceedings of the National Academy of Sciences| volume = 109| issue = 5| pages = 1396–1401| date = 2012-01-03|bibcode = 2012PNAS..109.1396B |pmc=3277151| doi-access = free}}</ref> A geological expedition has identified the exact place of the original discovery and found more specimens of the Khatyrka meteorite.<ref>Nadia Drake, [http://www.sciencenews.org/view/feature/id/345849/description/Prospecting_for_Quasicrystals Prospecting for Quasicrystals], ''Science News'', Print edition: Nov. 3, 2012; Vol.182 #9 (p. 24)/ Web edition: October 19, 2012</ref><ref>A second natural quasicrystal with a different (decagonal) structure has been identified in the samples, Bindi L., and al, ''Natural quasicrystal with decagonal symmetry'', [https://www.nature.com/srep/2015/150313/srep09111/full/srep09111.html Nature - Scientific Reports] 5, Article number: 9111 doi:10.1038/srep09111.</ref> The mineral's name derives from the Khatyrka ({{langx|ru|Хатырка}}) zone where it was discovered.<ref>Razin, L.V., N.S. Rudashevskii, and L.N. Vyal'sov. (1985) New natural intermetallic compounds of aluminum, copper and zinc—khatyrkite CuAI2, cupalite CuAI and zinc aluminides—from hyperbasites of dunite-harzburgite formation. Zap. Vses. Mineral. Obshch., 114,90–100 (in Russian). cf. (1986) Amer. Mineral., 71, 1278</ref> Its type specimen (defining sample) is preserved in the Mining Museum in Saint Petersburg, and parts of it can be found in other museums, such as Museo di Storia Naturale di Firenze.<ref name = handbook/><ref name=mindat/><ref name=j1/>

==Properties== thumb|left|upright|Khatyrkite viewed close to the tetragonal axis. Red balls are copper atoms. In the initial studies of khatyrkite, a negative correlation was observed between copper and zinc, i.e. the higher the copper the lower the zinc content and vice versa, which is why the formula was specified as {{chem2|(Cu,Zn)Al2}}.<ref name=names>{{cite journal|url=https://rruff.info/uploads/AM71_1277.pdf|journal=American Mineralogist|volume=71|pages =1277–1282|year=1986|title=New Mineral Names|author=Hawthorne, F. C.|display-authors=etal}}</ref> It was found later that iron can be substituted for zinc.<ref name=j1/> The mineral is opaque and has a steel-gray yellow tint in reflected light, similar to native platinum. Isotropic sections are light blue whereas anisotropic ones are blue to creamy pink. Strong optical anisotropy is observed when the crystals are viewed in polarized light. Khatyrkite forms dendritic, rounded or irregular grains, typically below 0.5 millimeter in size, which are intergrown with cupalite. They have a tetragonal symmetry with point group 4/m 2/m 2/m, space group I4/mcm and lattice constants ''a'' = 0.607(1) nm, ''c'' = 0.489(1) nm and four formula units per unit cell. The crystalline structure parameters are the same for khatyrkite and synthetic CuAl<sub>2</sub> alloy. The density, as calculated from XRD the lattice parameters, is 4.42 g/cm<sup>3</sup>. The crystals are malleable, that is they deform rather than break apart upon a strike; they have the Mohs hardness is between 5 and 6 and Vickers hardness is in the range 511–568&nbsp;kg/mm<sup>2</sup> for a 20–50&nbsp;gram load and 433–474&nbsp;kg/mm<sup>2</sup> for a 100&nbsp;gram load.<ref name=names/>

Khatyrkite and cupalite are accompanied by spinel, corundum, stishovite, augite, forsteritic olivine, diopsidic clinopyroxene and several Al-Cu-Fe metal alloy minerals. The presence of unoxidized aluminium in khatyrkite and association with the stishovite—a form of quartz which exclusively forms at high pressures of several tens gigapascals—suggest that the mineral was formed in a high-energy impact involving the object that became the Khatyrka meteorite.<ref name=mindat/><ref name=j1/><ref name=j2>{{cite journal|last=Bindi|first=Luca|author2=Paul J. Steinhardt|author3=Nan Yao|author4=Peter J. Lu|date=2009-06-05|title=Natural Quasicrystals|journal=Science|access-date=2009-08-07|pmid=19498165|doi=10.1126/science.1170827|volume=324|issue=5932|pages=1306–9|url=http://www.physics.princeton.edu/~steinh/naturalquasicrystals.html|bibcode=2009Sci...324.1306B|s2cid=14512017|url-access=subscription|archive-date=2011-09-27|archive-url=https://web.archive.org/web/20110927094940/http://www.physics.princeton.edu/~steinh/naturalquasicrystals.html|url-status=dead}}</ref> *{{cite magazine |author=Phillip Broadwith |date=4 June 2009 |title=Natural quasicrystals discovered |magazine=Chemistry World |url=https://www.rsc.org/chemistryworld/News/2009/June/04060904.asp}}

==Relation to quasicrystals== thumb|left|upright|X-ray diffraction pattern of the natural Al<sub>63</sub>Cu<sub>24</sub>Fe<sub>13</sub> quasicrystal.<ref name=j2/> Khatyrkite is remarkable in that it contains micrometre-sized grains of icosahedrite, the first known naturally occurring quasicrystal<ref>{{cite journal | last = Bindi | first = L. | author2 = Paul J. Steinhardt | author3 = Nan Yao | author4 = Peter J. Lu | title = Icosahedrite, Al<sub>63</sub>Cu<sub>24</sub>Fe<sub>13</sub>, the first natural quasicrystal | journal = American Mineralogist | volume = 96 | issue = 5–6 | pages = 928–931 | year = 2011 | url = http://wwwphy.princeton.edu/~steinh/icosahedriteAmMin.pdf | doi = 10.2138/am.2011.3758 | bibcode = 2011AmMin..96..928B | s2cid = 101152220 | access-date = 2012-10-21 | archive-date = 2012-04-04 | archive-url = https://web.archive.org/web/20120404114035/http://wwwphy.princeton.edu/~steinh/icosahedriteAmMin.pdf | url-status = dead }}</ref>—aperiodic and yet ordered in structure. The quasicrystal has a composition of Al<sub>63</sub>Cu<sub>24</sub>Fe<sub>13</sub> which is close to that of a well-characterized synthetic Al-Cu-Fe material.<ref name=j1/><ref>{{cite journal |last=Bindi|first=L.|title=Natural quasicrystals|journal=Science|year=2009|volume=324|issue=5932|pages=1306–1309|doi=10.1126/science.1170827|pmid=19498165|bibcode = 2009Sci...324.1306B |s2cid=14512017|display-authors=etal}}</ref> It is thought that the icosahedrite, like the khatyrkite, was formed in space in a collision involving the parent body of the meteorite.<ref name=Bindi2011/>

A second natural quasicrystal, called decagonite, Al<sub>71</sub>Ni<sub>24</sub>Fe<sub>5</sub> with a decagonal structure has been identified by Luca Bindi in the samples and announced in 2015.<ref>Bindi L., and al, ''Natural quasicrystal with decagonal symmetry'', [https://www.nature.com/srep/2015/150313/srep09111/full/srep09111.html Nature - Scientific Reports] 5, Article number: 9111 doi:10.1038/srep09111</ref><ref>Bindi, Luca, et al. "Decagonite, Al71Ni24Fe5, a quasicrystal with decagonal symmetry from the Khatyrka CV3 carbonaceous chondrite." American Mineralogist 100.10 (2015): 2340–2343.</ref> Another variant was announced the following year.<ref>Bindi L., Chaney Lin, Chi Ma & Paul J. Steinhardt, ''Collisions in outer space produced an icosahedral phase in the Khatyrka meteorite never observed previously in the laboratory'', [https://www.nature.com/articles/srep38117 Nature - Scientific reports], Dec. 2016</ref>

Quasicrystals were first reported in 1984<ref name=s>{{cite journal|doi=10.1103/PhysRevLett.53.1951|title=Metallic Phase with Long-Range Orientational Order and No Translational Symmetry|year=1984|last1=Shechtman|first1=D.|last2=Blech|first2=I.|last3=Gratias|first3=D.|last4=Cahn|first4=J.|journal=Physical Review Letters|volume=53|pages=1951|bibcode=1984PhRvL..53.1951S|issue=20|doi-access=free}}</ref> and named so by Dov Levine and Paul Steinhardt.<ref name=lay1>[https://www.scientificamerican.com/article.cfm?id=natural-quasicrystals Exotic Quasicrystal May Represent New Type of Mineral], Scientific American, 4 June 2009</ref> More than 100 quasicrystal compositions have been discovered by 2009—all synthesized in the laboratory. Steinhardt initiated a large-scale search for natural quasicrystals around the year of 2000 using the database of the International Centre for Diffraction Data. About 50 candidates were selected out of 9,000 minerals based on a set of parameters defined by the structure of the known quasicrystals. The corresponding samples were examined with X-ray diffraction and transmission electron microscopy but no quasicrystals were found. Widening of the search eventually included khatyrkite. A sample of the mineral was provided by Luca Bindi of the Museo di Firenze and was later proven to be part of the Russian holotype specimen. Mapping its chemical composition and crystalline structure revealed agglomerate of grains up to 0.1 millimeter in size of various phases, mostly khatyrkite, cupalite (zinc or iron containing), some yet unidentified Al-Cu-Fe minerals and the Al<sub>63</sub>Cu<sub>24</sub>Fe<sub>13</sub> quasicrystal phase. The quasicrystal grains were of high crystalline quality equal to that of the best laboratory specimens, as demonstrated by the narrow diffraction peaks. The mechanism of their formation is yet uncertain. The specific composition of the accompanying minerals and the location where the sample was collected—far from any industrial activities—confirm that the discovered quasicrystal is of natural origin.<ref name=j1/><ref name="j2"/>

==References== {{reflist|2}}

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==External links== *[https://webmineral.com/specimens/picshow.php?id=3746 Khatyrkite image and a TEM image of the quasicrystal]

Category:Native element minerals Category:Copper minerals Category:Aluminium minerals Category:Geology of Russia Category:Tetragonal minerals Category:Minerals in space group 140