Natural goethite

V.C. (1974) Surface structure of gibbsite, goethite and phosphated goethite. Nature 248 220-221... 

Yapp C. J. and Poths H. (1994) Productivity of pre-vascular biota inferred from Ee(C03)OH content of goethite. Nature 368, 49-51. 

Rosso KM, Becker U, Hochella MF Jr (1999) The interaction of pyrite 100 surfaces with O2 and H2O Fundamental oxidation mechanisms. Am Mineral 84 1549-1561 Russell JD, Parfitt RL, Fraser AR, Farmer VC (1974) Surface structures of gibbsite, goethite and phosphated goethite. Nature 248 220-221... 

On the basis of a number of physico-chemical methods (Mossbauer spectroscopy, electron diffraction, EXAFS) the iron cores of naturally occurring haemosiderins isolated from various iron-loaded animals and man (horse, reindeer, birds and human old age) were consistently shown to have ferrihydrite-like iron cores similar to those of ferritin (Ward et ah, 1992, 2000). In marked contrast, in the tissues of patients with two pathogenic iron-loading syndromes, genetic haemochromatosis and thalassaemia, the haemosiderins isolated had predominantly amorphous ferric oxide and goethite cores, respectively (Dickson etah, 1988 Mann etah, 1988 ... 

Despite the seeming exactitude of the mathematical development, the modeler should bear in mind that the double layer model involves uncertainties and data limitations in addition to those already described (Chapter 2). Perhaps foremost is the nature of the sorbing material itself. The complexation reactions are studied in laboratory experiments performed using synthetically precipitated ferric oxide. This material ripens with time, changing in water content and extent of polymerization. It eventually begins to crystallize to form goethite (FeOOH). 

Adsorption of heavy metal ions to the surface of goethite and of natural particles... 

The comparison between goethite and natural particles at pH = 8 shows a slightly larger tendency of the natural particles to bind Pb2+ than of goethite. 

Recent experiments have determined that the isotopic fractionation between adsorbed and dissolved Cr(VI) is very small (Ellis et al. submitted). In batch experiments, dissolved Cr(VI) was equilibrated with finely ground alumina or goethite. The results of these experiments should be appficable to natural settings, as oxides chemically similar to alumina and goethite provide the main adsorption sites for Cr(VI) anions. Because the analytical precision of the measurements was 0.2%o, it was necessary to amplify any isotopic shifts so that effects smaller than 0.1 %o could be detected. This was accompfished by repeating the sorption step ten or more times, so that a fractionation between dissolved and adsorbed Cr(VI) of 0.04%o was detectable at the 95% confidence level. 

Manceau A, Schlegel ML, Musso M, Sole VA, Gauthier C, Petit PE, Trolard F (2000) Crystal chemistry of trace elements in natural and synthetic goethite. Geochim Cosmochim Acta 64 3643-3661 Marchitto Jr. TM, Curry WB, Oppo DW (2000) Zinc concentrations in benthic foraminifera reflect seawater chemistry. Paleoceanogr 15 299-306. 

Yapp Cl (1983) Stable hydrogen isotopes in iron oxides - isotope effects associated with the dehydration of a natural goethite. Geochim Cosmochim Acta 47 1277-1287... 

Al-for-Fe substitution in natural goethites was originally discovered, with the aid of X-ray diffraction, in marine, oolithic, iron ores from the Jurassic era by Correns von Engelhardt as early as in 1941 and twenty years later found in soils by Norrish and Taylor (1961). Since then, a large number of studies has revealed that Al substitution in goethites from the weathered zone, e.g. in soils (see chap. 16), appears to be the rule rather than the exception. It should be noted that Al located in the struc-... 

Nothing is known about whether anions can enter the structure of synthetic goethites. Under ambient conditions in an aqueous system. Si interferes with the crystallization of goethite in both acid and alkaline media but, so far, no analytical proof of incorporation in the structure has been obtained (Glasauer, 1995). Furthermore, there is hardly any information about the replacement of Fe in natural goethites by cations other than A1 and by anions. Congruent release of Fe with... 

Fig. 4.6 High resolution electron micrograph of natural goethite a) Diamond-shaped cross sections of domains running along [010] and bounded by 101 faces. Lattice fringes correspond to the c -parameter. b) Higher magnification shows the a fringes (ca. 1 nm) and structural distortions. (Smith Eggleton, 1983 with permission courtesy R.A. Eggleton).

Goethite crystals produced by oxidation of Fe solutions at ambient temperature in neutral solution (Fig. 4.7 right) - a process likely to occur in nature - are usually much less developed and the crystals are smaller (MCLb 10 nm) than those obtained in alkaline Fe " solutions. If Al is taken up in the structure, these crystals become extremely small (MCL 5 nm) and show almost no particular habit. At higher pH (-12) the crystals are again acicular (MCL -30 nm) despite containing structural Al (Al/(Al-i-Fe) -0.3) they show internal disorder, however, and stars are frequent. This morphology is also observed for soil goethites (see Chap. 16). 

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