... in the oxide zone of 0.88 and 0.12 % . Goethite is the most abundant mineral in the oxide zone and the most important Ni-Co-Sc–bearing mineral, with median NiO, CoO, and Sc contents of 0.78 wt % , 0.07 wt % , and 58 ppm, respectively, and up to 2.77 wt % , 0.26 wt % , and 117 ppm. Maghemite is also widely...

... of hydroxyl-interlayed vermiculite. Among the pedogenic oxides the most frequent are goethite (α-FeOOH), indicated by yellowish colours (2.5Y–10YR; in the absence of hematite), and hematite (α-Fe 2 O 3 ), which imbues reddish colors (2.5YR–5R), even when present in very minor amounts. Maghemite (γ-Fe 2 O 3...

.... The enthalpies of wüstite (FeO) and magnetite (Fe 3 O 4 ) oxidation to hematite (Fe 2 O 3 ) were measured using oxidative drop solution calorimetry in which the final product is dissolved ferric oxide. Two methods were applied: drop solution calorimetry at 1073 K in lead borate solvent and at 973 K in sodium...

... % of Fe tot ) and Fe 3+ (30 % of Fe tot ), both octahedrally coordinated. The spectrum of thermally treated chrysotile clearly shows that the magnetic phases are now oxidized magnetite/maghemite and hematite, and the paramagnetic contribution is quite unaltered, though likely due to the newly formed...

...Figure 1. Simplified scheme for competitive production of magnetite (MGT), maghemite (MHT), and goethite (Goet.) and/or hematite (Hem.) from hydrous ferric oxides (HFO, e.g., ferrihydrite) through cycles of oxidizing and reducing conditions in the presence of dissimilatory iron reducing bacteria...

... of Dronino iron-ung metal weathering in clay sand (fragment No 1) demonstrated that in the internal oxidation layer there is formation of magnetite and maghemite with further transformation into goethite and other ferric hydrous oxides. The composition of the external oxidation layer was different for two...

...-mail: [email protected] 27 04 2000 27 09 1999 © 2000 American Mineralogist 2000 Ferrihydrite, which is also known as “amorphous ferric oxide” and “hydrous ferric oxide,” is a poorly crystalline Fe oxide that forms in low-temperature surface environments such as water wells, lake-bottom...

... is not simply a more crystalline form of 2LFh. † Contact for reprint requests. E-mail: [email protected] 09 11 2000 29 03 2000 © 2001 American Mineralogist 2001 Ferrihydrite is a nanocrystalline ferric oxide that commonly forms in near-surface environments such as lakes, hot...

... play a role in a number of environmentally important reactions, especially those involving redox sensitive contaminants such as Cr, As and Tc. It is therefore important to understand Fe oxidation state changes and magnetite transformations under different environmental settings. Maghemite (γ-Fe 2 O...

... of microwave remote sensing applications in the 0.3 to 300 GHz range. Of special interest are: the pseudosand effect caused by Fe-oxide cementation of clusters of soil particles; the mineralogy; and whether the soil magnetic susceptibility affected by ferromagnetic magnetite and maghemite interferes...

...Kirsty L. Grogan; Robert J. Gilkes; Bernd G. Lottermoser Abstract Evidence for the formation of maghemite from goethite due to a bushfire on acid sulfate soil at East Trinity, Australia, is presented. Oxidation of pyrite-bearing acid sulfate soils led to precipitation of goethite-impregnated leaf...

... of schwertmannite particles makes a complete structural interpretation difficult, but no evidence for a “modified” akaganeite structure was found in this study. END analyses suggest that most schwertmannite whiskers have a structure consistent with the maghemite-like structural component previously described...

... (maghemite) reoxidation depending on oxygen availability. As the formation of spinel requires the reduction of ferric iron, and thus a reductant such as a carbon source, this intermediate IV Fe-containing phase in the transformation of 2Fh into hematite cannot be used as evidence of the existence...

... of the ferromagnetic mineral increases toward the lower latitudes. Inasmuch as the mineral occurs in soils developed on limestone, it undoubtedly is a secondary ferromagnetic ferric oxide (possibly maghemite), and not detrital magnetite. Evidence that maghemite is the red pigment in some sandstone is cited by Hofer...

..., Pot Molle and Laasby) all occur at the feet of slopes and formed from Fe 2+ -containing seepage water. They contain 25– ~100% Fe oxides, originally consisting of ferrihydrite. The well-drained parts of the deposits are at present all dominated by goethite. Hematite and maghemite were also identified...

... enhancement of many paleosols ( Liu et al. 1992 ; Heller and Evans 1995 ; Maher 1998 ; Virina et al. 2000 ). The presence of maghemite in soils has been usually attributed to: (1) oxidation of magnetite; (2) dehydroxylation of lepidocrocite (γ-FeOOH); and (3) heating of goethite (α-FeOOH) in the presence...

... for ferrihydrite include ‘‘protoferrihydrite’’ (the name originally proposed for 2LFh), ‘‘amorphous ferric oxide,’’ and ‘‘hydrous ferric oxide’’ ( e.g., Chukhrov et al., 1973 ; Towe and Bradley, 1976; Farmer, 1992 ; Manceau et al., 1995 ). Although both natural and synthetic ferrihydrite occur in forms...

... and enthalpies of transformation of the studied phases relative to 1/2 α-Fe 2 O 3 ± 1/2H 2 O (liquid). The thermodynamic relations among the Fe-oxide minerals are mirrored in their mode of occurrence in nature. Despite their thermodynamic metastability, lepidocrocite and maghemite form readily in some...