Garnierite
Encyclopedia
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. 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 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
, 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.
. It found that each of the specimens analyzed fell into one of three groups: an Ni-talc to willemsiete (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. 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.
and 13.33(1), 27.03(2), 5.250(4) Å. The space group
is Pncn.
Based on the ionic radii and charge alone, Ni2+ should easily substitute for Mg2+ in octahedral coordination. 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. 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. At 106X 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
.
and higher mean index of refraction than lighter green garnierites, which most likely relates to the inclusion of more Ni in the 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.
-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 quartz
(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
, with the garnierite layer between 50 and 200 feet thick.
in 1867, announcing the discovery of nickel there. Garnierite was named for Jules Garnier in a paper by a man named A. 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 named a second mineral found in the same general area in New Caledonia noumeaite.
Serpentinite
Serpentinite is a rock composed of one or more serpentine group minerals. Minerals in this group are formed by serpentinization, a hydration and metamorphic transformation of ultramafic rock from the Earth's mantle...
ultramafic rocks. It forms by lateritic weathering of ultramafic rocks and occurs in many nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
laterite
Laterite
Laterites are soil types rich in iron and aluminium, formed in hot and wet tropical areas. Nearly all laterites are rusty-red because of iron oxides. They develop by intensive and long-lasting weathering of the underlying parent rock...
deposits in the world. It is an important nickel ore, having a large weight percent NiO. 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
Silicate minerals
The silicate minerals make up the largest and most important class of rock-forming minerals, constituting approximately 90 percent of the crust of the Earth. They are classified based on the structure of their silicate group...
, 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
Talc is a mineral composed of hydrated magnesium silicate with the chemical formula H2Mg34 or Mg3Si4O102. In loose form, it is the widely-used substance known as talcum powder. It occurs as foliated to fibrous masses, its crystals being so rare as to be almost unknown...
, sepiolite
Sepiolite
Sepiolite is a clay mineral, a complex magnesium silicate, a typical formula for which is Mg4Si6O152·6H2O. It can be present in fibrous, fine-particulate, and solid forms....
, smectite, or chlorite
Chlorite group
The chlorites are a group of phyllosilicate minerals. Chlorites can be described by the following four endmembers based on their chemistry via substitution of the following four elements in the silicate lattice; Mg, Fe, Ni, and Mn....
, and Ni-Mg silicates, with or without alumina, that have x-ray diffraction patterns typical of serpentine, talc, sepiolite, chlorite, vermiculite
Vermiculite
Vermiculite is a natural mineral that expands with the application of heat. The expansion process is called exfoliation and it is routinely accomplished in purpose-designed commercial furnaces. Vermiculite is formed by weathering or hydrothermal alteration of biotite or phlogopite...
or some mixture of them all.
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. 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 H2O(Mg,Ni)3Si4O10(OH)2 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 to find the composition of garnierite samples collected at the Falcondo mine in the Dominican RepublicDominican Republic
The Dominican Republic is a nation on the island of La Hispaniola, part of the Greater Antilles archipelago in the Caribbean region. The western third of the island is occupied by the nation of Haiti, making Hispaniola one of two Caribbean islands that are shared by two countries...
. It found that each of the specimens analyzed fell into one of three groups: an Ni-talc to willemsiete (up to 25 weight percent Ni) group, an Ni-lizardite to nepouite
Népouite
Népouite is a rare nickel silicate mineral which has the apple green colour typical of such compounds. It was named by E Glasser in 1907 after the place where it was first described , the Népoui Mine, Népoui, Nouméa Commune, Northern Province, New Caledonia...
(up to 34 weight percent Ni) group and an Ni-sepiolite to falcondoite (up to 24 weight percent Ni) group. 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.
Structure
Garnierite is generally a fine grained mineral with poor crystalline structure. The unit cell parameters, found using TEM analysis, are 13.385(4), 26.955(9), 5.271(3) ÅÅngström
The angstrom or ångström, is a unit of length equal to 1/10,000,000,000 of a meter . Its symbol is the Swedish letter Å....
and 13.33(1), 27.03(2), 5.250(4) Å. The space group
Space group
In mathematics and geometry, a space group is a symmetry group, usually for three dimensions, that divides space into discrete repeatable domains.In three dimensions, there are 219 unique types, or counted as 230 if chiral copies are considered distinct...
is Pncn.
Based on the ionic radii and charge alone, Ni2+ should easily substitute for Mg2+ in octahedral coordination. 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. 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. At 106X 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
Chrysotile
Chrysotile or white asbestos is the most commonly encountered form of asbestos, accounting for approximately 95% of the asbestos in place in the United States and a similar proportion in other countries. It is a soft, fibrous silicate mineral in the serpentine group of phyllosilicates; as such, it...
or lizardite in their structures, while 10 Å types usually resemble pimelite
Pimelite
Pimelite was discredited as a mineral species by the International Mineralogical Association 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...
.
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, from soft and brittle to hard enough to carve into figurines and the like. 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 gravitySpecific gravity
Specific gravity is the ratio of the density of a substance to the density of a reference substance. Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance is nearly always water for...
and higher mean index of refraction than lighter green garnierites, which most likely relates to the inclusion of more Ni in the 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.
Geologic Occurrence
Light colored garnierite is an alteration of olivineOlivine
The mineral olivine is a magnesium iron silicate with the formula 2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface....
-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 quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
(chrysoprase
Chrysoprase
Chrysoprase, chrysophrase or chrysoprasus is a gemstone variety of chalcedony that contains small quantities of nickel. Its color is normally apple-green, but varies to deep green. The darker varieties of chrysoprase are also referred to as prase...
, 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
Riddle, Oregon
Riddle is a city in Douglas County, Oregon, United States. The population was 1,014 at the 2000 census.-Geography:According to the United States Census Bureau, the city has a total area of , all of it land.Riddle was founded by George Abner Riddle....
, garnierite is found as a weathering product of the underlying peridotite
Peridotite
A peridotite is a dense, coarse-grained igneous rock, consisting mostly of the minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium, reflecting the high proportions of magnesium-rich olivine, with appreciable iron...
, with the garnierite layer between 50 and 200 feet thick.
Origin of the Name
Jules Garnier, a French geologist, published his work on the geology of New CaledoniaNew Caledonia
New Caledonia is a special collectivity of France located in the southwest Pacific Ocean, east of Australia and about from Metropolitan France. The archipelago, part of the Melanesia subregion, includes the main island of Grande Terre, the Loyalty Islands, the Belep archipelago, the Isle of...
in 1867, announcing the discovery of nickel there. Garnierite was named for Jules Garnier in a paper by a man named A. 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 named a second mineral found in the same general area in New Caledonia noumeaite.