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The formation of hematite from amorphous Fe(III)hydroxide in aqueous systems at pH 6 and 70°C, both with and without oxalate, was followed by kinetic measurements, electron microscopy, i.r. spectroscopy and thermal analysis. In the absence of oxalate, small amorphous particles coalesce into aggregates which eventually become single crystals of hematite. When oxalate is present, crystal growth is much faster and does not proceed through the intermediate stage of aggregation. Aggregates, when formed, consist of groups of single crystals. It is suggested that oxalate accelerates the nucleation of hematite crystals by acting as a template, the Fe-Fe distance in Fe-oxalate ions being similar to that in hematite.

Vermiculite (particles 2 to 0.2 microns in diameter), after being treated with H‐Amberlite IR‐120, aged for 97 days, and suspended in 1NKNO3, showed a third buffer range between pH 5.5 and 7.6 on continuous titration with dilute NaOH. This third buffer range is attributed to neutralization of excess protons of Al‐OH2groups in positively charged hydroxy aluminum polymers formed on interlayer surfaces of vermiculite under the influence of their negative charge. This conclusion was reached on the basis of observance of the same additional buffer range in titration curves of partially neutralized and aged AlCl3‐solutions (OH/Al ratios ranging from 1 to 2.25) and of vermiculite treated with the aged hydroxy aluminum solutions. The hydroxy aluminum polymers are only partly exchangeable by 1NKCl, and also are fairly resistant to treatment of the clay with H‐resin. The X‐ray diffractogram of the vermiculite shows an enhanced 7.2Å. (002) peak after H‐resin treatment and aging, indicating more interlayer material. Hydroxy aluminum treated vermiculite and aged acid vermiculite showed reduced collapsibility on K saturation and heat treatment, pointing also to the occurrence of the hydroxy polymers in the interlayer position. Compared with similar reactions with montmorillonite from bentonite previously reported, these compounds form with greater avidity in vermiculite, have a greater stability to subsequent H‐resin treatment, and have a higher resistance to exchange in KCl. These differences presumably arise because of the higher net negative charge of the vermiculite layers. Soil clays which give X‐ray diffraction evidence of interlayer hydroxy aluminum show the third buffer range on treatment with H resin, without aging time or treatment with hydroxy aluminum solutions.

Ferruginous concretions from various Australian and German soils and samples of bog iron ore from various European localities were examined by X-ray diffraction and electron microprobe techniques. The association between phosphorus and iron in these samples was looked at from the point of view of differences in iron mineralogy and genesis. When surface area is considered it appears that hematite, goethite and possibly maghemite show phosphorus adsorption levels in the same order of magnitude as those obtained on synthetic preparations of these minerals. In most cases a high phosphorus content is associated with a high iron, but the converse is not true, so that although the iron minerals are definite sinks for the phosphorus in the environment a linear relation cannot be expected due to the variation in time and spatial distribution of these two elements. In the younger European soils the phosphorus/iron ratios are generally higher (average 0.015), reaching values as high as 0.05 in some bog iron ores formed in gleys, whereas in the older Australian soils the average ratio is 0.002.

Various methods for the extraction of pedogenic oxides of Al, Fe, and Mn are described and their applicability for interpreting soil profile genesis is demonstrated. Representative great soil groups can be differentiated by typical depth functions of the pedogenic oxides. Furthermore, intergrades between the end members, which cannot be recognized in the field, have distinctly different depth functions. As an example crypto podzolization can be recognized by a maximum of “free Al” in the subsoil. By means of these depth functions three types of imperfectly drained Gray Brown Podzolic Soils with and without lateral iron removal and with lateral iron addition may be distinguished.

The conversion of lepidocrocite (-γFeOOH) to its more stable polymorph, goethite (αFeOOH) was followed by observing changes in crystal morphology, oxalate solubility, surface area and X-ray diffraction. In conjunction, kinetics were measured as functions of surface area, temperature, alkalinity and seeding with goethite crystals. The results suggest that the transformation is not topochemical, but proceeds through the solution phase. The main steps governing the rate of transformation are, (1) the dissolution of lepidocrocite, and (2) the formation of goethite nuclei and subsequent growth. Either of these processes can be rate-determining under appropriate conditions. La conversion de la lépidocrocite (γ FeOOH) en son polymorphe plus stable, la goethite (αFeOOH) a été suivie en observant les changements de la morphologie cristalline, de la solubilité à l’oxalate, de la surface spécifique et de la diffraction X. Parallèlement, on a effectué des mesures cinétiques en fonction de la surface spécifique, de la température, de l’alcalinité et de l’ensemencement avec des cristaux de goethite. Les résultats suggèrent que la transformation n’est pas topochimique, mais qu’elle se fait par l’intermédiaire d’une phase solution. Les étapes principales qui gouvernent la vitesse de la transformation sont, (1) la dissolution de la lépidocrocite, et (2) la formation des nucléi de goethite et leur croissance ultérieure. Chacun de ces processus peut être un facteur limitant de la vitesse dans des conditions appropriées. Die Umwandlung von synthetischem Lepidokrokit (γ FeOOH) in seine stabilere polymorphe Form Goethit (a FeOOH) wurde verfolgt durch Beobachtung von Änderungen in der Kristallmorphologie, der Oxalatlöslichkeit, der spezifischen und der Röntgenbeugung. In diesem Zusammenhang wurde die Kinetik als Funktion Oberfläche des Ausgangs-Lepidokrokits, der Temperatur, der Alkalinität und des Impfens mit Goethitkristallen gemessen. Die Ergebnisse deuten darauf hin, dass die Umwandlung nicht topochemisch ist, sondern über die Lösungsphase erfolgt. Die Hauptstufen, die die Umwandlungsgeschwindigkeit bestimmen, sind, (1) die Auflösung von Lepidokrokit, und (2) die Bildung von Goethitkeimen und deren Wachstum. Je nach den Bedingungen kann der eine oder der andere dieser Prozesse geschwindigkeitsbestimmend sein. Превращение лепидокрокита (γ РеООН) в его более стабильное полиморфное соединение—гетит (α РеООН) исследовалось наблюдением изменений кристаллической морфологии, растворимости оксалатов, поверхности и дифракции рентгеновских лучей. В связи с этим измерялась кинетика, как функции площади поверхности, температуры, мелочности и затравливания кристаллами гетита. Результаты указывают на то, что это превращение не топохимическое, а происходит через фазу растворения. Основные стадии, управляющие скоростью превращения, следующие: (1) растворение лепидокрокита и (2) образование ядер гетита с последующим ростом. При соответствующих условиях любой из этих процессов может определять скорость превращения.