New insights into the nature of glauconite

Glauconite must be assessed as mica-rich mica-smectite R3 interstratified mineral, with the pure end-member mica also having intrinsic K-deficient chemical characteristics (K+ ~ 0.8 apfu). This assertion is in accordance with our X-ray diffraction (XRD) and high-resolution tranmission electron microscopy (HRTEM) studies and chemical analyses by electron probe microanalysis (EPMA) of mature glauconites in Cenozoic Antarctic sediments that indicate that: (1) It consists of a glauconite-smectite (R3 ordered) mixed-layer silicate, composed mainly of mica-type layers (>90%), but displaying slightly different proportions of Fe(III)-smectite layers (<10%). (2) More mature glaucony grains are characterized by major K+ and VIFe2+ (mica layers) and minor VIFe3+ (smectite layers) content in the interstratified glauconite-smectite. (3) Potassium is stabilized at the interlayer site by the octahedrally coordinated Fe2+. (4) Microtexture of the glauconite crystals are comparable with those of other micas and illite minerals, with straight, defect-free lattice fringes of ~10 Å spacings glauconite packets characteristic of mica with minor interstratified poorly crystalline smectite layers. In addition, our new findings give insights into the glauconitization process and at the same time investigate the potassium-deficient character of the dioctahedral mica “glauconite.” These findings show that glauconite crystallizes by a layer-growth mechanism at the expense of a poorly crystalline smectite precursor and that smectiteto-glauconite transformations are accompanied by a gradually higher octahedral charge deficiency (Fe2+/Fe3+) stabilized by K+ uptake into the interlayer sheet.

Chemical Reaction Characteristics of HDTMA+ Cations in Interlayer Space of Vermiculite Crystal Layers

Hydrophlogopite, a regular interstratified mineral with 1:1 ratio of vermiculite and phlogopite crystal layers, was modified with sodium and organically intercalated with HDTMAB, and then the samples were examined with XRD. Based on the theoretical geometric dimensions of organic cations, the structure and arrangement model of HDTMA+ cation in the interlayer space of vermiculite crystal layers were studied, the reaction mechanism of organic intercalation was also discussed. The results show that HDTMA+ cations enter into the interlayer space of vermiculite crystal layers only without exchange with the cations in the interlayer space of phlogopite crystal layers, and that the arrangement models of HDTMA+ cations in the interlayer space of vermiculite crystal layers varies with the added amount of HDTMAB. When the added amount is small, the arrangement model of HDTMA+ cations in the interlayer space of vermiculite crystal layers is lateral-bilayer, and when the added amount is larger, the arrangement model is paraffin-type monolayer.

Influence of parent material on clay minerals formation in Podzols of Trentino, Italy

The formation of clay minerals was investigated in Spodosols developed in the subalpine belt, with similar exposure, climate and age, but deriving from different parent materials. All the soils were classified as Haplic Podzols and showed the characteristic eluviation and illuviation features of Fe, Al and organic carbon. However, varying parent material lithology led to different clay mineral assemblages in the soil. Smectite could be found in the E horizons of soils developed from granodiorite and tonalite materials. Its formation was strongly dependent on the presence of chlorite in the parent material. If nearly no other 2:1 mineral components, such as chlorite, are present in the lower soil horizons, then a residual micaceous mineral becomes the dominant clay mineral. The latter derives from a mica-vermiculite interstratified mineral.

Layer charge characteristics of smectites from Vertosols (Vertisols) of New South Wales

Premature senescence in cotton has been attributed to K deficiency in the cotton soils of Australia. The availability, release, and fixation of K+ in soils are mainly dependent on the clay mineralogy and layer charge characteristics of 2 : 1 clay minerals. There is a little information on the mineralogy and charge characteristics of the cotton growing soils (Vertosols) of Australia. The aims of this study were to determine the clay mineralogy, the layer charge density, and layer charge distribution of some cotton growing soils by chemical and X-ray diffraction methods.Most soil clays contain abundant smectite associated with small amounts of mica, kaolinite, and an interstratified mineral. The total layer charge as determined by the alkylammonium method ranged between 0.55 and 0.67 mol(–)/(O10(OH)2), indicating a high interlayer charge density. The layer charge of smectites from different valleys and for different size fractions was similar. The Greene-Kelly test showed that most of the charge originated in the tetrahedral sheet. The chemical analysis indicates that the smectite is an iron-rich beidellite, which has possibly formed from the weathering of mica.

Long-term weathering of silicates in a sandy soil at Nordmoen, southern Norway

Weathering processes have been studied in a podzol profile developed on sand during a postglacial period of 9400 years. Due to disintegration of rock fragments, the particle-size distribution has changed markedly in the upper part of the profile, and minerals have been transferred from sand fractions to silt and clay fractions. The most important weathering processes are the total breakdown of trioctahedral chlorite and biotite, and the transformation of dioctahedral mica (muscovite-phengite) to a regularly interstratified mineral, and further to Al-vermiculite or smectite. By using quartz as an internal standard, the annual loss due to weathering was found to be 3·2 g/m2. The release of elements due to silicate weathering was calculated from depletion curves, and the average annual release of Na + K + Mg + Ca for the postglacial period was 19 mEq/m2.

Study of a chlorite-smectite interstratified mineral by means of the Inter program

A chlorite-smectite interstratified mineral in a pottery stone from Niwatorizawa mine, Izushi-Cho, Hyogo Prefecture (Japan), has been studied by means of Fourier transform methods, together with interlamellar sorption of ethylene glycol and glycerol. The calculations were carried out with the INTER program (using an Olivetti M-24 personal computer with MS-DOS operating system) which allows the analysis of two-component interstratified structures by two Fourier transform based methods: the X-ray diffraction intensity function method, and the interlayer distances distribution function method. The material studied contains a 1:1 chlorite-smectite interstratification and shows a marked tendency to alternation, i.e., the interstratification is almost regular.

SIGNIFICANCE OF CORRENSITE IN SOILS OF SOUTHEASTERN ONTARIO

Samples were collected from Ap/Ah and Bm horizons of 10 soils from southeastern Ontario. The soil reaction ranged from medium acid to mildly alkaline. Mineralogical analysis of the various particle-size fractions showed the presence of corrensite, talc and graphite in the assemblage. These three minerals were also present in large amounts in marble outcrops, where they were formed by hydrothermal alteration and metamorphism. The significance of inherited interstratified minerals in the soils was considered from the analytical aspect: the first-order basal reflection should be confirmed because higher orders could be confounded with other mineral reflections; and from the pedogenetic aspect: failing to recognize an inherited interstratified mineral would be misleading in the interpretation of soil evolution. Key words: Grenville province, interstratified mineral, corrensite, talc, graphite, inherited minerals

Computer Program for Analysing Interstratified Structures by Fourier Transform Methods

A computer program for analysing two-component interstratified structures by two different Fourier transform methods is described. The first method consists of the calculation of the X-ray diffraction intensity function, and in the second one (direct method) the distribution function of interlayer distances is calculated. The programs have been written in compiled GWBASIC for an Olivetti M-24 microcomputer (MS-DOS operating system), and they may also be run on any IBM compatible personal computer. As an example, this program is applied for the analysis of a chlorite-smectite interstratified mineral.

The soil clays of Great Britain: I. England and Wales

The mineralogy of the clay fractions (<2 µm) of the major soils of England and Wales is reviewed, and the data presented in terms of the 1:250 000 National Soil Map. Most soils developed in pre-Rhaetic sediments are dominated by mica with lesser amounts of chlorite and kaolin. Exceptions are soils developed in calcareous Coal Measure shales which have significant smectite contents, and freely drained soils in Keuper Marl which contain swelling chlorite, sepiolite and palygorskite. Soils developed in post-Triassic sediments are dominated generally by expansible minerals, except for those developed in Lower Lias and Estuarine Series rocks (Jurassic) which are dominated by mica and kaolin respectively. The presence of loess in soils seems to be associated with the occurrence of a complex interstratified mineral with X-ray diffraction properties akin to vermiculite. Weathering of soil clays is most marked in the wetter uplands, but over most of lowland England is detectable only by slight changes in non-exchangeable potassium content and cation-exchange capacity towards the soil surface. Applications of soil clay mineralogy in the fields of plant nutrition and soil mechanics are discussed, in particular the production of maps showing mineralogical provinces.