Garnierite

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Garnierite

Garnierite is a general name for a green nickel ore which is found in pockets and veins within weathered and 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. [1] [2] 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 silicates, [1] [3] 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, talc, sepiolite, smectite, or chlorite, [4] 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. [5]

Contents

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. [6] In 1973, another study found that chemical analysis of garnierite samples yields non-stoichiometric formulae that can be reduced to formulas like those of talc and serpentine. The authors suggested a talc monohydrate formula of (Mg,Ni)3Si4O10(OH)2·H2O for the talc-like garnierite. [4] 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. [5] 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. [7] 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. [2] According to X-ray and thermal analysis, the garnierites of the Ural deposits are multiphase formations and consist of a serpentinites (pecoraite 2McI, chrysotile 2McI, chrysotile 2OrcI, lisardite 6T, lisardite 1T, népouite - nickel lisardite 1T), chlorites (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 magnesiochromite and rivsite are among the sporadic minerals found in them. [8]

Structure

Garnierite is generally a fine grained mineral with poor crystalline structure. [4] The unit cell parameters, found using transmission electron microscopy (TEM) analysis, are 13.385(4), 26.955(9), 5.271(3) Å and 13.33(1), 27.03(2), 5.250(4) Å. The space group is Pncn. [7]

Based on the ionic radii and charge alone, Ni2+ should easily substitute for Mg2+ in octahedral coordination. [3] [9] 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. [2]

Garnierite is a layer silicate. [4] [6] [10] 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. [4] [6] At 106 × 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. [10] 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. [10] 7 Å type garnierites usually resemble chrysotile or lizardite in their structures, while 10 Å types usually resemble pimelite. [4] [10]

Physical properties

Garnierite is a green mineral, ranging from light yellow-green to dark green. [3] [5] The color comes from the presence of nickel in the mineral structure for magnesium. [4] 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. [11] Some species of garnierite stick to the tongue and dissolve readily in water or even on the tongue. [11] Garnierite commonly has a colloform texture, typical of minerals that fill open spaces from a solution. [7] In general, darker green garnierites have higher Ni content, higher specific gravity and higher mean index of refraction than lighter green garnierites, which most likely relates to the inclusion of more Ni in their crystalline structure. The 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. [1]

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. [1] 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. [7] [12] 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 %). [7] 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. [7] In the garnierite deposits near Riddle, Oregon, garnierite is found as a weathering product of the underlying peridotite, with the garnierite layer between 50 and 200 ft (15 and 61 m) thick. [1]

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. [3] Garnierite was named for Jules Garnier in a paper by Archibald Liversidge in 1874. [1] 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. [1] [11]

See also

Related Research Articles

<span class="mw-page-title-main">Mineral</span> Crystalline chemical element or compound formed by geologic processes

In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.

<span class="mw-page-title-main">Talc</span> Hydrated magnesium phyllosilicate mineral

Talc, or talcum, is a clay mineral, composed of hydrated magnesium silicate with the chemical formula Mg3Si4O10(OH)2. Talc in powdered form, often combined with corn starch, is used as baby powder. This mineral is used as a thickening agent and lubricant. It is an ingredient in ceramics, paints, and roofing material. It is a main ingredient in many cosmetics. It occurs as foliated to fibrous masses, and in an exceptionally rare crystal form. It has a perfect basal cleavage and an uneven flat fracture, and it is foliated with a two-dimensional platy form.

<span class="mw-page-title-main">Brucite</span> Magnesium hydroxide mineral

Brucite is the mineral form of magnesium hydroxide, with the chemical formula Mg(OH)2. It is a common alteration product of periclase in marble; a low-temperature hydrothermal vein mineral in metamorphosed limestones and chlorite schists; and formed during serpentinization of dunites. Brucite is often found in association with serpentine, calcite, aragonite, dolomite, magnesite, hydromagnesite, artinite, talc and chrysotile.

<span class="mw-page-title-main">Serpentine subgroup</span> Family of hydrous ferromagnesian minerals

Serpentine subgroup are greenish, brownish, or spotted minerals commonly found in serpentinite. They are used as a source of magnesium and asbestos, and as decorative stone. The name comes from the greenish colour and smooth or scaly appearance from the Latin serpentinus, meaning "serpent rock".

<span class="mw-page-title-main">Clay mineral</span> Fine-grained aluminium phyllosilicates

Clay minerals are hydrous aluminium phyllosilicates (e.g. kaolin, Al2Si2O5(OH)4), sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces.

<span class="mw-page-title-main">Chlorite group</span> Type of mineral

The chlorites are the group of phyllosilicate minerals common in low-grade metamorphic rocks and in altered igneous rocks. Greenschist, formed by metamorphism of basalt or other low-silica volcanic rock, typically contains significant amounts of chlorite.

<span class="mw-page-title-main">Ultramafic rock</span> Type of igneous and meta-igneous rock

Ultramafic rocks are igneous and meta-igneous rocks with a very low silica content, generally >18% MgO, high FeO, low potassium, and are composed of usually greater than 90% mafic minerals. The Earth's mantle is composed of ultramafic rocks. Ultrabasic is a more inclusive term that includes igneous rocks with low silica content that may not be extremely enriched in Fe and Mg, such as carbonatites and ultrapotassic igneous rocks.

<span class="mw-page-title-main">Cummingtonite</span> Silicate mineral

Cummingtonite is a metamorphic amphibole with the chemical composition (Mg,Fe2+
)
2(Mg,Fe2+
)
5Si
8O
22(OH)
2, magnesium iron silicate hydroxide.

<span class="mw-page-title-main">Palygorskite</span> Magnesium aluminium phyllosilicate mineral

Palygorskite or attapulgite is a magnesium aluminium phyllosilicate with the chemical formula (Mg,Al)2Si4O10(OH)·4(H2O) that occurs in a type of clay soil common to the Southeastern United States. It is one of the types of fuller's earth. Some smaller deposits of this mineral can be found in Mexico, where its use is tied to the manufacture of Maya blue in pre-Columbian times.

<span class="mw-page-title-main">Komatiite</span> Ultramafic mantle-derived volcanic rock

Komatiite is a type of ultramafic mantle-derived volcanic rock defined as having crystallised from a lava of at least 18 wt% MgO. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. Komatiite was named for its type locality along the Komati River in South Africa, and frequently displays spinifex texture composed of large dendritic plates of olivine and pyroxene.

<span class="mw-page-title-main">Sepiolite</span> Soft and porous white magnesium silicate clay mineral

Sepiolite, also known in English by the German name meerschaum ( MEER-shawm, -⁠shəm; German: [ˈmeːɐ̯ʃaʊm](listen); meaning "sea foam"), is a soft white clay mineral, often used to make tobacco pipes (known as meerschaum pipes). A complex magnesium silicate, a typical chemical formula for which is Mg4Si6O15(OH)2·6H2O, it can be present in fibrous, fine-particulate, and solid forms.

Talc carbonates are a suite of rock and mineral compositions found in metamorphosed ultramafic rocks.

Lateritic nickel ore deposits are surficial, weathered rinds formed on ultramafic rocks. They account for 73% of the continental world nickel resources and will be in the future the dominant source for the mining of nickel.

<span class="mw-page-title-main">Iddingsite</span>

Iddingsite is a microcrystalline rock that is derived from alteration of olivine. It is usually studied as a mineral, and consists of a mixture of remnant olivine, clay minerals, iron oxides, and ferrihydrites. Debates over iddingsite's non-definite crystal structure caused it to be de-listed as an official mineral by the IMA; thus, it is properly referred to as a rock.

<span class="mw-page-title-main">Népouite</span> Nickel ore from the serpentine family (phyllosilicate)

Népouite is a rare nickel silicate mineral which has the apple green colour typical of such compounds. It was named by the French mining engineer Edouard Glasser in 1907 after the place where it was first described, the Népoui Mine, Népoui, Poya Commune, North Province, New Caledonia. The ideal formula is Ni3(Si2O5)(OH)4, but most specimens contain some magnesium, and (Ni,Mg)3(Si2O5)(OH)4 is more realistic. There is a similar mineral called lizardite in which all of the nickel is replaced by magnesium, formula Mg3(Si2O5)(OH)4. These two minerals form a series; intermediate compositions are possible, with varying proportions of nickel to magnesium.

<span class="mw-page-title-main">Pimelite</span> Nickel-rich smectite deprecated as mineral species in 2006

Pimelite was discredited as a mineral species by the International Mineralogical Association (IMA) in 2006, in an article which suggests that “pimelite” specimens are probably willemseite, or kerolite. This was a mass discreditation, and not based on any re-examination of the type material. Nevertheless, a considerable number of papers have been written, verifying that pimelite is a nickel-dominant smectite. It is always possible to redefine a mineral wrongly discredited.

Antigorite Monoclinic mineral

Antigorite is a lamellated, monoclinic mineral in the phylosilicate serpentine subgroup with the ideal chemical formula of (Mg,Fe2+)3Si2O5(OH)4. It is the high-pressure polymorph of serpentine and is commonly found in metamorphosed serpentinites. Antigorite, and its serpentine polymorphs, play an important role in subduction zone dynamics due to their relative weakness and high weight percent of water (up to 13 weight % H2O). It is named after its type locality, the Geisspfad serpentinite, Valle Antigorio in the border region of Italy/Switzerland and is commonly used as a gemstone in jewelry and carvings.

Falcondoite, a member of the sepiolite group, was first discovered in the Dominican Republic, near the town of Bonao. The mineral was found in a deposit mined by Falconbridge Dominica, and so was named "falcondoite" after the company. Falcondoite is frequently associated with sepiolite, garnierite, talc, and serpentine, and is commonly nickel-bearing. While the chemical formula for falcondoite can vary, the mineral must contain more nickel than magnesium to be considered its own species. The ideal chemical formula for falcondoite is (Ni,Mg)4Si6O15(OH)2·6H2O.

References

  1. 1 2 3 4 5 6 7 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.
  2. 1 2 3 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.
  3. 1 2 3 4 Faust, G.T. (1966) The hydrous nickel-magnesium silicates – The garnierite group. The American Mineralogist, 51, 279-298.
  4. 1 2 3 4 5 6 7 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.
  5. 1 2 3 Springer, G. (1974) Compositional and structural variations in garnierites. Canadian Mineralogist, 12, 381-388.
  6. 1 2 3 Shimoda, S. (1964) Mineralogical studies on garnierite and aquacreptite. Clay Science, 2, 1, 8-21.
  7. 1 2 3 4 5 6 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
  8. ↑ Talovina, I.V., Lazarenkov, V.G., Ryzhkova, S.O., Ugolkov, V.L. and Vorontsova, N.I. (2008) Garnierite in nickel deposits of the Urals. Lithology and Mineral Resources, 6, 650–658. https://link.springer.com/article/10.1134/S0024490208060060
  9. ↑ Faye, G.H. (1974) Optical absorption spectrum of Ni2+ in garnierite: A discussion. Canadian Mineralogist, 12, 389-393.
  10. 1 2 3 4 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.
  11. 1 2 3 Liversidge, A. (1880) Notes upon some minerals from New Caledonia. Journal and Proceedings of the Royal Society of New South Wales, 14, 227-246.
  12. ↑ Villanova-de-Benavent, Cristina; Proenza, Joaquín A.; Galí, Salvador; García-Casco, Antonio; Tauler, Esperança; Lewis, John F.; Longo, Francisco (2014). "Garnierites and garnierites: Textures, mineralogy and geochemistry of garnierites in the Falcondo Ni-laterite deposit, Dominican Republic". Ore Geology Reviews. 58: 91–109. doi:10.1016/j.oregeorev.2013.10.008. hdl: 2445/160419 .
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