Garnierite is a general name for a green nickel ore which is found in pockets and veins within weathered and serpentinized

ultramafic Ultramafic rocks (also referred to as ultrabasic rocks, although the terms are not wholly equivalent) are igneous and meta-igneous rocks with a very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium, and are composed ...

rocks. It forms by lateritic weathering of ultramafic rocks and occurs in many

nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow t ...

laterite Laterite is both a soil and a rock type rich in iron and aluminium and is commonly considered to have formed in hot and wet tropical areas. Nearly all laterites are of rusty-red coloration, because of high iron oxide content. They develop by ...

deposits in the world. It is an important nickel ore, having a large weight percent NiO.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.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. 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 In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name ...

,Faust, G.T. (1966) The hydrous nickel-magnesium silicates – The garnierite group. The American Mineralogist, 51, 279-298. 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 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 a ...

, sepiolite, smectite, or

chlorite The chlorite ion, or chlorine dioxide anion, is the halite with the chemical formula of . A chlorite (compound) is a compound that contains this group, with chlorine in the oxidation state of +3. Chlorites are also known as salts of chlorou ...

,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. and Ni-Mg silicates, with or without alumina, that have x-ray diffraction patterns typical of serpentine, talc, sepiolite, chlorite,

vermiculite Vermiculite is a hydrous phyllosilicate mineral which undergoes significant expansion when heated. Exfoliation occurs when the mineral is heated sufficiently, and commercial furnaces can routinely produce this effect. Vermiculite forms by the we ...

or some mixture of them all.Springer, G. (1974) Compositional and structural variations in garnierites. Canadian Mineralogist, 12, 381-388.

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.Shimoda, S. (1964) Mineralogical studies on garnierite and aquacreptite. Clay Science, 2, 1, 8-21. In 1973, another study found that chemical analysis of garnierite samples yields non-stoichiometric formulae that can be reduced to formulas like those of

and serpentine. The authors suggested a talc monohydrate formula of for the talc-like garnierite. 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. In 2008, yet another study used

X-ray diffraction X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...

to find the composition of garnierite samples collected at the Falcondo mine in the

Dominican Republic The Dominican Republic ( ; es, República Dominicana, ) is a country located on the island of Hispaniola in the Greater Antilles archipelago of the Caribbean region. It occupies the eastern five-eighths of the island, which it shares with ...

. 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 Lizardite is a mineral from the serpentine group with formula , and the most common type of mineral in the group. It is also a member of the kaolinite-serpentine group. Népouite and lizardite form a series; intermediate compositions are pos ...

to nepouite (up to 34 weight percent Ni) group and an Ni-sepiolite to falcondoite (up to 24 weight percent Ni) group.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 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 A solid solution, a term popularly used for metals, is a homogenous mixture of two different kinds of atoms in solid state and have a single crystal structure. Many examples can be found in metallurgy, geology, and solid-state chemistry. The wor ...

between Ni- sepiolite and falcondoite, with samples analyzed showing between 3 and 77 percent falcondoite composition. According to X-ray and thermal analysis, the garnierites of the Ural deposits are multiphase formations and consist of a serpentinites ( pecoraite 2McI,

chrysotile Chrysotile or white asbestos is the most commonly encountered form of asbestos, accounting for approximately 95% of the asbestos in the United StatesOccupational Safety and Health Administration, U.S. Department of Labor (2007)29 C.F.R.&nb ...

2McI, chrysotile 2OrcI, lisardite 6T, lisardite 1T,

népouite 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 type locality), the Né ...

- nickel lisardite 1T), chlorites ( clinochlore IIB, sepiolite, palygorskite), clay minerals ( nontronite, saponite,

montmorillonite Montmorillonite is a very soft phyllosilicate group of minerals that form when they precipitate from water solution as microscopic crystals, known as clay. It is named after Montmorillon in France. Montmorillonite, a member of the smectite gro ...

), minerals of the

mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into extremely thin elastic plates. This characteristic is described as perfect basal cleavage. Mica is ...

supergroup (

, vilemsite, clintonite, annite, phlogopite) and

quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical f ...

Calcite Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scratc ...

sauconite Sauconite is a complex phyllosilicate mineral of the smectite clay group, formula Na0.3 Zn3( Si Al)4 O10(O H)2·4 H2O. It forms soft earthy bluish white to red-brown monoclinic crystals typically massive to micaceous in habit. It has a Mohs har ...

, beidellite, halloysite,

thomsonite Thomsonite is the name of a series of tecto-silicate minerals of the zeolite group. Prior to 1997, thomsonite was recognized as a mineral species, but a reclassification in 1997 by the International Mineralogical Association changed it to a seri ...

goethite Goethite (, ) is a mineral of the diaspore group, consisting of iron(III) oxide-hydroxide, specifically the "α" polymorph. It is found in soil and other low-temperature environments such as sediment. Goethite has been well known since ancient t ...

maghemite Maghemite (Fe2O3, γ-Fe2O3) is a member of the family of iron oxides. It has the same spinel ferrite structure as magnetite and is also ferrimagnetic. It is sometimes spelled as "maghaemite". ''Maghemite'' can be considered as an Fe(II)-deficie ...

opal Opal is a hydrated amorphous form of silica (SiO2·''n''H2O); its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Due to its amorphous property, it is classified as a mineraloid, unlike crystalline form ...

moganite Moganite is an oxide mineral with the chemical formula Si O2 ( silicon dioxide) that was discovered in 1976. It was initially described as a new form of silica from specimens found in the Barranco de Medio Almud, in the municipality of Mogán ...

, nickel hexahydrite, accessory

magnesiochromite Chromite is a crystalline mineral composed primarily of iron(II) oxide and chromium(III) oxide compounds. It can be represented by the chemical formula of FeCr2O4. It is an oxide mineral belonging to the spinel group. The element magnesium can su ...

and rivsite are among the sporadic minerals found in them.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

Structure

Garnierite is generally a fine grained mineral with poor

crystalline structure In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric patterns ...

. The

unit cell In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector, for example) does not necessaril ...

parameters, found using

transmission electron microscopy Transmission electron microscopy (TEM) is a microscopy technique in which a beam of electrons is transmitted through a specimen to form an image. The specimen is most often an ultrathin section less than 100 nm thick or a suspension on a ...

(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 In mathematics, physics and chemistry, a space group is the symmetry group of an object in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of an object that leave it uncha ...

is Pncn. Based on the

ionic radii Ionic radius, ''r''ion, is the radius of a monatomic ion in an ionic crystal structure. Although neither atoms nor ions have sharp boundaries, they are treated as if they were hard spheres with radii such that the sum of ionic radii of the cation ...

and charge alone, Ni²⁺ should easily substitute for Mg²⁺ in octahedral coordination.Faye, G.H. (1974) Optical absorption spectrum of Ni²⁺ in garnierite: A discussion. Canadian Mineralogist, 12, 389-393. 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. Garnierite is a layer silicate.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. 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 An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

powder diffraction Powder diffraction is a scientific technique using X-ray, neutron, or electron diffraction on powder or microcrystalline samples for structural characterization of materials. An instrument dedicated to performing such powder measurements is call ...

studies. The serpentine-like variants have 7 Å basal spacings while the talc-like variants have a basal spacing of 10 Å. 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. 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. 7 Å type garnierites usually resemble

in their structures, while 10 Å types usually resemble pimelite.

Physical properties

Garnierite is a green mineral, ranging from light yellow-green to dark green. The color comes from the presence of nickel in the mineral structure for magnesium. Noumeaite (later determined to be a member of the garnierite family) varies in

hardness In materials science, hardness (antonym: softness) is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion. In general, different materials differ in their hardness; for example hard ...

, from soft and brittle to hard enough to carve into figurines and the like.Liversidge, A. (1880) Notes upon some minerals from New Caledonia. Journal and Proceedings of the Royal Society of New South Wales, 14, 227-246. Some species of garnierite stick to the tongue and dissolve readily in water or even on the tongue. Garnierite commonly has a colloform texture, typical of minerals that fill open spaces from a

solution Solution may refer to: * Solution (chemistry), a mixture where one substance is dissolved in another * Solution (equation), in mathematics ** Numerical solution, in numerical analysis, approximate solutions within specified error bounds * Solutio ...

. In general, darker green garnierites have higher Ni content, higher

specific gravity Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water at its dens ...

and higher mean

index of refraction In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, or ...

than lighter green garnierites, which most likely relates to the inclusion of more Ni in their

. The

of garnierite ranges from approximately 2.5 to 3. The mean index of refraction of garnierite ranges from approximately 1.563 to 1.601.

Geologic occurrence

Light colored garnierite is an alteration of

olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers qui ...

-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. 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. X-ray diffraction of samples from that mine show that garnierite veins include sepiolite-falcondoite and

( chrysoprase, a green variety of quartz with a nickel content of less than 2 weight %).

Breccias Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of d ...

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. In the garnierite deposits near Riddle, Oregon, garnierite is found as a weathering product of the underlying

peridotite Peridotite ( ) is a dense, coarse-grained igneous rock consisting mostly of the silicate minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium (Mg2+), reflecting the high pr ...

, with the garnierite layer between thick.

Origin of the name

Jules Garnier, a French geologist, published his work on the geology of

New Caledonia ) , anthem = "" , image_map = New Caledonia on the globe (small islands magnified) (Polynesia centered).svg , map_alt = Location of New Caledonia , map_caption = Location of New Caledonia , mapsize = 290px , subdivision_type = Sovereign st ...

in 1867, announcing the discovery of nickel there. Garnierite was named for Jules Garnier in a paper by

Archibald Liversidge Archibald Liversidge FRS FRSE FRSNSW LLD (17 November 1847 – 26 September 1927) was an English-born chemist and a co-founder of the Australasian Association for the Advancement of Science. Early life Liversidge was born at Turnham Green, ...

in 1874. 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.

References