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 usua ...

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

nickel Nickel is a chemical element; it has 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 slo ...

laterite Laterite is a soil 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 intensive and prolo ...

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 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 is also used for an ...

,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 . Talc in powdered form, often combined with corn starch, is used as baby powder. This mineral is used as a thickening agent and lubricant ...

, sepiolite,

smectite A smectite (; ; ) is a mineral mixture of various swelling sheet silicates (phyllosilicates), which have a three-layer 2:1 (TOT) structure and belong to the clay minerals. Smectites mainly consist of montmorillonite, but can often contain secon ...

, or

chlorite The chlorite ion, or chlorine dioxide anion, is the halite (oxyanion), 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 s ...

,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 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 Non-stoichiometric compounds are chemical compounds, almost always solid inorganic compounds, having chemical element, elemental composition whose proportions cannot be represented by a ratio of small natural numbers (i.e. an empirical formula); ...

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 diffraction is a generic term for phenomena associated with changes in the direction of X-ray beams due to interactions with the electrons around atoms. It occurs due to elastic scattering, when there is no change in the energy of the waves. ...

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

Dominican Republic The Dominican Republic is a country located on the island of Hispaniola in the Greater Antilles of the Caribbean Sea in the Atlantic Ocean, North Atlantic Ocean. It shares a Maritime boundary, maritime border with Puerto Rico to the east and ...

. 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.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 homogeneous mixture of two compounds in solid state and having a single crystal structure. Many examples can be found in metallurgy, geology, and solid-state chemistry. The word "solutio ...

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 2McI, chrysotile 2OrcI, lisardite 6T, lisardite 1T, népouite – nickel lisardite 1T), chlorites ( clinochlore IIB, sepiolite, palygorskite), clay minerals ( nontronite,

saponite Saponite is a trioctahedral mineral of the smectite group. Its chemical formula is . It is soluble in sulfuric acid. It was first described in 1840 by Lars Fredrik Svanberg, Svanberg. Varieties of saponite are griffithite, bowlingite and sobotk ...

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 grou ...

, vermiculite), 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 fragile elastic plates. This characteristic is described as ''perfect basal cleavage''. Mica is co ...

supergroup (

, vilemsite, clintonite, annite, phlogopite) and

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

Calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

, sauconite, beidellite,

halloysite Halloysite is an aluminosilicate clay mineral with the empirical formula Al2Si2O5(OH)4. Its main constituents are oxygen (55.78%), silicon (21.76%), aluminium (20.90%), and hydrogen (1.56%). It is a member of the kaolinite group. Halloysite typic ...

, thomsonite,

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 formula as hematite, but the same spinel ferrite structure as magnetite () and is also ferrimagnetic. It is sometimes spelled as "maghaemite". ''Maghemite'' ...

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

, moganite, nickel hexahydrite, accessory magnesiochromite and rivsite are among the sporadic minerals found in them.

Structure

Garnierite is generally a fine grained mineral with poor

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

. The unit cell 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 g ...

(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 a repeating pattern in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of the pattern that ...

is Pncn. Based on the ionic radii 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 (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...

powder diffraction 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 chrysotile or lizardite 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 plastic deformation, such as an indentation (over an area) or a scratch (linear), induced mechanically either by Pressing (metalworking), pressing or abrasion ...

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

specific gravity Relative density, also called specific gravity, is a dimensionless quantity defined as the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for solids and liquids is nea ...

and higher mean index of refraction 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 minerals, silicate with the chemical formula . It is a type of Nesosilicates, nesosilicate or orthosilicate. The primary component of the Earth's upper mantle (Earth), upper mantle, it is a com ...

-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 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 New Caledonia ( ; ) is a group of islands in the southwest Pacific Ocean, southwest of Vanuatu and east of Australia. Located from Metropolitan France, it forms a Overseas France#Sui generis collectivity, ''sui generis'' collectivity of t ...

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