Ferrihydrite | |
---|---|
General | |
Category | Oxide minerals |
Formula (repeating unit) | (Fe3+)2O3·0.5H2O |
IMA symbol | Fhy [1] |
Strunz classification | 4.FE.35 |
Dana classification | 04.03.02.02 |
Crystal system | Hexagonal |
Crystal class | Dihexagonal pyramidal (6mm) H-M symbol: (6mm) |
Space group | P63mc |
Unit cell | a = 5.958, c = 8.965 [Å]; Z = 1 |
Identification | |
Formula mass | 168.70 g/mol |
Color | Dark brown, yellow-brown |
Crystal habit | Aggregates, microscopic crystals |
Streak | Yellow-brown |
Diaphaneity | Opaque |
Density | 3.8 g/cm3 |
References | [2] [3] [4] [5] |
Ferrihydrite (Fh) is a widespread hydrous ferric oxyhydroxide mineral at the Earth's surface, [6] [7] and a likely constituent in extraterrestrial materials. [8] It forms in several types of environments, from freshwater to marine systems, aquifers to hydrothermal hot springs and scales, soils, and areas affected by mining. It can be precipitated directly from oxygenated iron-rich aqueous solutions, or by bacteria either as a result of a metabolic activity or passive sorption of dissolved iron followed by nucleation reactions. [9] Ferrihydrite also occurs in the core of the ferritin protein from many living organisms, for the purpose of intra-cellular iron storage. [10] [11]
Ferrihydrite only exists as a fine grained and highly defective nanomaterial. The powder X-ray diffraction pattern of Fh contains two scattering bands in its most disordered state, and a maximum of six strong lines in its most crystalline state. The principal difference between these two diffraction end-members, commonly named two-line and six-line ferrihydrites, is the size of the constitutive crystallites. [12] [13] The six-line form has been classified as a mineral by the IMA in 1973 [14] with the nominal chemical formula 5Fe
2O
3·9H
2O. [15] Other proposed formulas are Fe
5HO
8·4H
2O [16] and Fe
2O
3·2FeO(OH)·2.6H
2O. [17] However, its formula is fundamentally indeterminate as its water content is variable. The two-line form is also called hydrous ferric oxides (HFO).
Due to the nanoparticulate nature of ferrihydrite, the structure has remained elusive for many years and is still a matter of controversy. [18] [19] [20] Drits et al., using X-ray diffraction data, [12] proposed in 1993 a multiphase structure model for six-line ferrihydrite with three components: (1) defect-free crystallites (f-phase) with double-hexagonal stacking of oxygen and hydroxyl layers (ABAC sequence) and disordered octahedral Fe occupancies, (2) defective crystallites (d-phase) with a short-range feroxyhite-like (δ-FeOOH) structure, and (3) subordinate ultradisperse hematite (α-Fe2O3). The diffraction model has been confirmed in 2002 by neutron diffraction, [21] and the three components were observed by high-resolution transmission electron microscopy. [22] [23] [24] A single phase model for both ferrihydrite and hydromaghemite [25] has been proposed by Michel et al., [26] [27] in 2007–2010, based on pair distribution function (PDF) analysis of x-ray total scattering data. The structural model, isostructural with the mineral akdalaite (Al10O14(OH)2), contains 20% tetrahedrally and 80% octahedrally coordinated iron. Manceau et al. showed in 2014 [28] that the Drits et al. [12] model reproduces the PDF data as well as the Michel et al. [26] model, and he suggested in 2019 [20] that the tetrahedral coordination arises from maghemite and magnetite impurities observed by electron microscopy. [23] [29] [30]
Because of the small size of individual nanocrystals, Fh is nanoporous yielding large surface areas of several hundred square meters per gram. [31] In addition to having a high surface area to volume ratio, Fh also has a high density of local or point defects, such as dangling bonds and vacancies. These properties confer a high ability to adsorb many environmentally important chemical species, including arsenic, lead, phosphate, and organic molecules (e.g., humic and fulvic acids). [32] [33] [34] [35] Its strong and extensive interaction with trace metals and metalloids is used in industry, at large-scale in water purification plants, as in North Germany and to produce the city water at Hiroshima, and at small scale to clean wastewaters and groundwaters, for example to remove arsenic from industrial effluents and drinking water. [36] [37] [38] [39] [40] Its nanoporosity and high affinity for gold can be used to elaborate Fh-supported nanosized Au particles for the catalytic oxidation of CO at temperatures below 0 °C. [41] Dispersed six-line ferrihydrite nanoparticles can be entrapped in a vesicular state to increase their stability. [42]
Ferrihydrite is a metastable mineral. It is known to be a precursor of more crystalline minerals like hematite and goethite [43] [44] [45] [46] by aggregation-based crystal growth. [47] [48] However, its transformation in natural systems generally is blocked by chemical impurities adsorbed at its surface, for example silica as most of natural ferrihydrites are siliceous. [49]
Under reducing conditions as those found in gley soils, or in deep environments depleted in oxygen, and often with the assistance of microbial activity, ferrihydrite can be transformed in green rust, a layered double hydroxide (LDH), also known as the mineral fougerite. However, a short exposure of green rust to atmospheric oxygen is sufficient to oxidize it back to ferrihydrite, making it a very elusive compound.
Better crystallized and less hydrated iron oxy-hydroxides are amongst others:
Hematite, also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of Fe
2O
3. It has the same crystal structure as corundum (Al
2O
3) and ilmenite (FeTiO
3). With this it forms a complete solid solution at temperatures above 950 °C (1,740 °F).
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 times for its use as a pigment. Evidence has been found of its use in paint pigment samples taken from the caves of Lascaux in France. It was first described in 1806 based on samples found in the Hollertszug Mine in Herdorf, Germany. The mineral was named after the German polymath and poet Johann Wolfgang von Goethe (1749–1832).
Iron oxides are chemical compounds composed of iron and oxygen. Several iron oxides are recognized. Often they are non-stoichiometric. Oxyhydroxides are a related class of compounds, perhaps the best known of which is rust.
Magnesite is a mineral with the chemical formula MgCO
3. Iron, manganese, cobalt, and nickel may occur as admixtures, but only in small amounts.
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 (Fe3O4) and is also ferrimagnetic. It is sometimes spelled as "maghaemite".
Todorokite is a complex hydrous manganese oxide mineral with generic chemical formula (Na,Ca,K,Ba,Sr)
1-x(Mn,Mg,Al)
6O
12·3-4H
2O. It was named in 1934 for the type locality, the Todoroki mine, Hokkaido, Japan. It belongs to the prismatic class 2/m of the monoclinic crystal system, but the angle β between the a and c axes is close to 90°, making it seem orthorhombic. It is a brown to black mineral which occurs in massive or tuberose forms. It is quite soft with a Mohs hardness of 1.5, and a specific gravity of 3.49 – 3.82. It is a component of deep ocean basin manganese nodules.
Romanèchite ((Ba,H2O)2(Mn4+,Mn3+)5O10) is the primary constituent of psilomelane, which is a mixture of minerals. Most psilomelane is not pure romanechite, so it is incorrect to consider them synonyms. Romanèchite is a valuable ore of manganese, which is used in steelmaking and sodium battery production. It has a monoclinic crystal structure, a hardness of 6 and a specific gravity of 4.7–5. Romanèchite's structure consists of 2 × 3 tunnels formed by MnO6 octahedra.
Birnessite (nominally MnO2·nH2O), also known as δ-MnO2, is a hydrous manganese dioxide mineral with a chemical formula of Na0.7Ca0.3Mn7O14·2.8H2O. It is the main manganese mineral species at the Earth's surface, and commonly occurs as fine-grained, poorly crystallized aggregates in soils, sediments, grain and rock coatings (e.g., desert varnish), and marine ferromanganese nodules and crusts. It was discovered at Birness, Aberdeenshire, Scotland.
Iron(III) oxide-hydroxide or ferric oxyhydroxide is the chemical compound of iron, oxygen, and hydrogen with formula FeO(OH).
Red beds are sedimentary rocks, typically consisting of sandstone, siltstone, and shale, that are predominantly red in color due to the presence of ferric oxides. Frequently, these red-colored sedimentary strata locally contain thin beds of conglomerate, marl, limestone, or some combination of these sedimentary rocks. The ferric oxides, which are responsible for the red color of red beds, typically occur as a coating on the grains of sediments comprising red beds. Classic examples of red beds are the Permian and Triassic strata of the western United States and the Devonian Old Red Sandstone facies of Europe.
In inorganic chemistry, mineral hydration is a reaction which adds water to the crystal structure of a mineral, usually creating a new mineral, commonly called a hydrate.
Schwertmannite is an iron-oxyhydroxysulfate mineral with an ideal chemical formula of Fe8O8(OH)6(SO4) · n H2O or Fe3+
16O
16(OH,SO4)
12–13·10-12H
2O. It is an opaque tetragonal mineral typically occurring as brownish yellow encrustations. It has a Mohs hardness of 2.5 - 3.5 and a specific gravity of 3.77 - 3.99.
The surface color of the planet Mars appears reddish from a distance because of rusty atmospheric dust. From close up, it looks more of a butterscotch, and other common surface colors include golden, brown, tan, and greenish, depending on minerals.
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.
Green rust is a generic name for various green crystalline chemical compounds containing iron(II) and iron(III) cations, the hydroxide (HO−
) anion, and another anion such as carbonate (CO2−
3), chloride (Cl−
), or sulfate (SO2−
4), in a layered double hydroxide structure. The most studied varieties are
Maricite or marićite is a sodium iron phosphate mineral (NaFe2+PO4), that has two metal cations connected to a phosphate tetrahedron. It is structurally similar to the much more common mineral olivine. Maricite is brittle, usually colorless to gray, and has been found in nodules within shale beds often containing other minerals.
Buserite is a hydrated layered manganese-oxide mineral with nominal chemical formula MnO2·nH2O. It was named after Swiss chemist professor W. Buser, who first identified it in 1952 in deep-sea manganese nodules. Buser named it 10 Å manganate because the periodicity in the layer stacking direction was 10 Å. It was renamed buserite in 1970 by the nomenclature commission of the International Mineralogical Association (IMA).
CM chondrites are a group of chondritic meteorites which resemble their type specimen, the Mighei meteorite. The CM is the most commonly recovered group of the 'carbonaceous chondrite' class of meteorites, though all are rarer in collections than ordinary chondrites.
Alain Manceau, born September 19, 1955, is a French environmental mineralogist and biogeochemist. He is known for his research on the structure and reactivity of nanoparticulate iron and manganese oxides and clay minerals, on the crystal chemistry of strategic metals and rare-earth elements, and on the structural biogeochemistry of mercury in natural systems, animals, and humans.
Iron ochre or iron ocher (Ancient Greek: ὠχρός, pale yellow, orange) — at least three iron ore minerals, common abrasives and pigments with a red-brown or brown-orange hue and the powdery consistency of ocher, were known under such a trivial name. The term “iron ocher” was primarily used among mineral collectors, geologists, miners and representatives of related craft professions. It may refer to: