Editing Garnierite

{{Short description|Nickel layer silicate}}
[[Image:Garniérite Camp Des Sapins.jpg|thumb|Garnierite]]

'''Garnierite''' is a general name for a green nickel ore which is found in pockets and veins within weathered and [[serpentinite|serpentinized]] [[ultramafic]] rocks. It forms by lateritic weathering of ultramafic rocks and occurs in many [[nickel]] [[laterite]] deposits in the world. It is an important nickel ore, having a large weight percent NiO.<ref name=Pecora>Pecora, W.T., Hobbs, S.W. and Murata, J.K. (1949) Variations in garnierite from the nickel deposit near Riddle, Oregon. Economic Geology, 44, 13–23.</ref><ref name=Roque>Roqué-Rosell, J., Villanova-de-Benavent, C., Proenza, J.A., Tauler, E. and Galí,S. (2011) Distribution and speciation of Ni in sepiolite-falcondoite-type “garnierite” by EXAFS. Macla, 15, 183–184.</ref> As garnierite is not a valid mineral name according to the Commission on New Minerals, Nomenclature and Classification (CNMNC), no definite composition or formula has been universally adopted. Some of the proposed compositions are all hydrous Ni-Mg [[silicate minerals|silicates]],<ref name=Pecora/><ref name=Faust>Faust, G.T. (1966) The hydrous nickel-magnesium silicates – The garnierite group. The American Mineralogist, 51, 279–298.</ref> a general name for the Ni-Mg hydrosilicates which usually occur as an intimate mixture and commonly includes two or more of the following minerals: [[serpentine group|serpentine]], [[talc]], [[sepiolite]], [[smectite]], or [[chlorite group|chlorite]],<ref name=Brindley1973>Brindley, G.W. and Hang, P.T. (1973) The nature of garnierites – I Structures, chemical compositions and color characteristics. Clays and Clay Minerals, 21, 27–40.</ref> and Ni-Mg silicates, with or without alumina, that have x-ray diffraction patterns typical of serpentine, talc, sepiolite, chlorite, [[vermiculite]] or some mixture of them all.<ref name=Springer>Springer, G. (1974) Compositional and structural variations in garnierites. Canadian Mineralogist, 12, 381–388.</ref>

==Composition==
Various studies have examined the composition of garnierite. In 1964, a study was done on the composition of a talc-like garnierite and found the composition to be close to the compositions of [[stevensite]] and [[sepiolite]], but with partial replacement of the Mg content by Ni.<ref name=Shimoda>Shimoda, S. (1964) Mineralogical studies on garnierite and aquacreptite. Clay Science, 2, 1, 8–21.</ref> In 1973, another study found that chemical analysis of garnierite samples yields [[Non-stoichiometric compound|non-stoichiometric]] formulae that can be reduced to formulas like those of [[talc]] and [[Serpentine subgroup|serpentine]]. The authors suggested a talc monohydrate formula of {{chem2|(Mg,Ni)3Si4O10(OH)2·H2O}} for the talc-like garnierite.<ref name=Brindley1973/> A third study found Mg, Si, Fe, Ni and Al in the samples studied. The author determined that the compositions of all of his garnierite samples lie between the serpentine solid solution series and the sepiolite solid solution series.<ref name=Springer/> In 2008, yet another study used [[X-ray diffraction]] to find the composition of garnierite samples collected at the Falcondo mine in the [[Dominican Republic]]. It found that each of the specimens analyzed fell into one of three groups: an Ni-talc to [[willemseite]] (up to 25 weight percent Ni) group, an Ni-[[lizardite]] to [[nepouite]] (up to 34 weight percent Ni) group and an Ni-sepiolite to [[falcondoite]] (up to 24 weight percent Ni) group.<ref name=Proenza>Proenza, J.A. et al. (2008) Garnierite mineralization from Falconda Ni-laterite deposit (Dominican Republic), Revista de la Sociedad Espanola de Mineralogia. Macia no.9 Septiembre 08. http://www.ehu.es/sem/macla_pdf/macla9/macla9_197.pdf {{Webarchive|url=https://web.archive.org/web/20110526091311/http://www.ehu.es/sem/macla_pdf/macla9/macla9_197.pdf |date=2011-05-26 }}</ref> In 2011, the most recent study performed used Extended X-ray Absorption Fine Structure ([[EXAFS]]) analysis to determine the composition of their garnierite samples. It found that garnierite has an almost complete [[solid solution]] between Ni-[[sepiolite]] and [[falcondoite]], with samples analyzed showing between 3 and 77 percent falcondoite composition.<ref name=Roque/> According to X-ray and thermal analysis, the garnierites of the [[Ural Mountains|Ural]] deposits are multiphase formations and consist of a serpentinites ([[pecoraite]] 2McI, [[chrysotile]] 2McI, chrysotile 2OrcI, [[Lizardite|lisardite]] 6T, lisardite 1T, [[népouite]] – nickel lisardite 1T), [[Chlorite group|chlorites]] ([[Chlorite group|clinochlore]] IIB, [[sepiolite]], [[palygorskite]]), clay minerals ([[nontronite]], [[saponite]], [[montmorillonite]], [[vermiculite]]), minerals of the [[mica]] supergroup ([[talc]], vilemsite, [[clintonite]], [[annite]], [[phlogopite]]) and [[quartz]]. [[Calcite]], [[sauconite]], beidellite, [[halloysite]], [[thomsonite]], [[goethite]], [[maghemite]], [[opal]], [[moganite]], nickel [[hexahydrite]], accessory [[Chromite|magnesiochromite]] and rivsite are among the sporadic minerals found in them.<ref name="Talovina">{{Cite journal |last=Talovina |first=I. V. |last2=Lazarenkov |first2=V. G. |last3=Ryzhkova |first3=S. O. |last4=Ugol’kov |first4=V. L. |last5=Vorontsova |first5=N. I. |date=2008-11-01 |title=Garnierite in nickel deposits of the Urals |url=https://doi.org/10.1134/S0024490208060060 |journal=Lithology and Mineral Resources |language=en |volume=43 |issue=6 |pages=588–595 |doi=10.1134/S0024490208060060 |issn=1608-3229 |access-date=2024-05-04 |archive-date=2024-05-04 |archive-url=https://web.archive.org/web/20240504052739/https://link.springer.com/article/10.1134/S0024490208060060 |url-status=live |url-access=subscription }}</ref>

==Structure==
Garnierite is generally a fine grained mineral with poor [[Crystal structure|crystalline structure]].<ref name=Brindley1973/> The [[unit cell]] parameters, found using [[transmission electron microscopy]] (TEM) analysis, are 13.385(4), 26.955(9), 5.271(3) [[angstrom|Å]] and 13.33(1), 27.03(2), 5.250(4) Å. The [[space group]] is Pncn.<ref name=Proenza/>

Based on the [[Ionic radius|ionic radii]] and charge alone, Ni<sup>2+</sup> should easily substitute for Mg<sup>2+</sup> in [[Octahedral molecular geometry|octahedral coordination]].<ref name=Faust/><ref name=Faye>Faye, G.H. (1974) Optical absorption spectrum of Ni<sup>2+</sup> in garnierite: A discussion. Canadian Mineralogist, 12, 389–393.</ref> The fact that Ni readily substitutes for Mg in garnierite explains why as NiO content goes up, MgO content goes down. The nickel in garnierite is not evenly distributed throughout the structure, but is concentrated in small zones of nickel surrounded by magnesium zones.<ref name=Roque/>
 
Garnierite is a [[Silicate mineral|layer silicate]].<ref name=Brindley1973/><ref name=Shimoda/><ref name=Uyeda>Uyeda, N., Hang, P.T. and Brindley, G.W. (1973) The nature of garnierites – II Electron-optical study. Clays and Clay Minerals, 21, 41–50.</ref> The main difference between the serpentine-like and talc-like variants of garnierite is the spacing between layers in the structure, seen in [[X-ray]] [[powder diffraction]] studies. The serpentine-like variants have 7 Å basal spacings while the talc-like variants have a basal spacing of 10 Å.<ref name=Brindley1973/><ref name=Shimoda/> At 10<sup>6</sup> × magnifications, the 7 and 10 Å layer spacings (d(001)) are obvious and measureable, with the 7 Å spacings being better defined than the 10 Å spacings.<ref name=Uyeda/> 7 Å, serpentine-like minerals show rod and tube shaped particles, as well as platy particles and fluffy particles that are most likely aggregates while the 10 Å variety shows much less variation in particles, showing only platy and fluffy forms with very few tube or rod shaped particles. Some particles exhibit interstratification of 7 and 10 Å spacings. There is no correlation between NiO content and the shapes of the particles in the mineral.<ref name=Uyeda/> 7 Å type garnierites usually resemble [[chrysotile]] or [[lizardite]] in their structures, while 10 Å types usually resemble [[pimelite]].<ref name=Brindley1973/><ref name=Uyeda/>

==Physical properties==
Garnierite is a green mineral, ranging from light yellow-green to dark green.<ref name=Faust/><ref name=Springer/> The color comes from the presence of nickel in the mineral structure for magnesium.<ref name=Brindley1973/> [[Noumeaite]] (later determined to be a member of the garnierite family) varies in [[hardness]], from soft and brittle to hard enough to carve into figurines and the like.<ref name=Liversidge>Liversidge, A. (1880) Notes upon some minerals from New Caledonia. Journal and Proceedings of the Royal Society of New South Wales, 14, 227–246.</ref> Some species of garnierite stick to the tongue and dissolve readily in water or even on the tongue.<ref name=Liversidge/> Garnierite commonly has a colloform texture, typical of minerals that fill open spaces from a [[Solution (chemistry)|solution]].<ref name=Proenza/> In general, darker green garnierites have higher Ni content, higher [[specific gravity]] and higher mean [[Refractive index|index of refraction]] than lighter green garnierites, which most likely relates to the inclusion of more Ni in their [[Crystal structure|crystalline structure]]. The [[Relative density|specific gravity]] of garnierite ranges from approximately 2.5 to 3. The mean index of refraction of garnierite ranges from approximately 1.563 to 1.601.<ref name=Pecora/>

==Geologic occurrence==
Light colored garnierite is an alteration of [[olivine]]-rich rock to a clay-like mineral poor in nickel, light green to bright green garnierite is a result of the leaching of manganese oxide, magnesium, nickel and iron from the original dark green garnierite, rich in nickel, which was deposited by groundwater.<ref name=Pecora/> This leads to a very common occurrence of garnierite as fracture fillings of millimeter to centimeter thick veins or as a fabric or coatings at the Falcondo mine in the Dominican Republic.<ref name=Proenza/><ref>{{cite journal|last1=Villanova-de-Benavent|first1=Cristina|last2=Proenza|first2=Joaquín A.|last3=Galí|first3=Salvador|last4=García-Casco|first4=Antonio|last5=Tauler|first5=Esperança|last6=Lewis|first6=John F.|last7=Longo|first7=Francisco|title=Garnierites and garnierites: Textures, mineralogy and geochemistry of garnierites in the Falcondo Ni-laterite deposit, Dominican Republic|journal=Ore Geology Reviews|date=2014|volume=58|pages=91–109|doi=10.1016/j.oregeorev.2013.10.008|hdl=2445/160419|s2cid=128481921 |hdl-access=free}}</ref> X-ray diffraction of samples from that mine show that garnierite veins include sepiolite-falcondoite and [[quartz]] ([[chrysoprase]], a green variety of quartz with a nickel content of less than 2 weight %).<ref name=Proenza/> [[Breccias]] found in faults at the Falcondo mine contain garnierite clasts cemented together by a secondary deposition of garnierite, which is evidence of syn-tectonic deposition of garnierite.<ref name=Proenza/> In the garnierite deposits near [[Riddle, Oregon]], garnierite is found as a weathering product of the underlying [[peridotite]], with the garnierite layer between {{convert|50|and|200|ft|abbr=on}} thick.<ref name=Pecora/>

==Origin of the name==
[[Jules Garnier]], a French geologist, published his work on the geology of [[New Caledonia]] in 1867, announcing the discovery of nickel there.<ref name=Faust/> Garnierite was named for Jules Garnier in a paper by [[Archibald Liversidge]] in 1874.<ref name=Pecora/> When Liversidge sent a copy of his paper to Garnier, Garnier replied that the new mineral [[noumeite]] being described in the paper sounded very much like a mineral he had described in his 1869 paper. Liversidge decided to name the new mineral garnierite in honor of Garnier and gave the name noumeaite to a second mineral found in the same general area in New Caledonia.<ref name=Pecora/><ref name=Liversidge/>

==See also==
* [[List of minerals]]
* [[List of minerals named after people]]

==References==
{{Reflist}}

[[Category:Nickel minerals]]
[[Category:Magnesium minerals]]
[[Category:Silicate minerals]]