Vermiculite minerals are locally available in the Mozambique Belt of Tanzania but are not currently commercially exploited. In part this may be due to lack of any precise characterization. This study was carried out as a first step to assess the suitability of these vermiculites for crop production by characterization of their mineralogical and chemical compositions. X-ray diffraction and scanning electron microscopy combined with an energy-dispersive X-ray system were used to establish the mineralogy. Electron microprobe analysis and inductively coupled plasma-mass spectrometry were used to study the chemical compositions and to identify any possible issues related to chemical composition that might affect their use if applied as soil conditioners. The samples were characterized as vermiculites and hydrobiotites with a wide variety of accessory minerals. Accessory minerals that might be of some concern are galena, fibrous amphiboles and sepiolite. The total levels of Ni in all vermiculites, and Cr in some, were also found to be high relative to common European standards and this might limit their potential as soil conditioners. It is clear that a field assessment of the bioavailability of various elements would be necessary before decisions relating to potential agricultural use could be made.

A new structural model for ferrihydrite that challenges the standard ferrihydrite model established by X-ray diffraction and confirmed by neutron diffraction and single-crystal electron nanodiffraction was recently proposed by Michel et al. (2007a) from the simulation of the pair distribution function obtained by Fourier transformation of diffraction data measured at λ = 0.137 Å. The new ferrihydrite model is isostructural to akdalaite (Al10O14(OH)2), a mineral having the Baker-Figgis δ-isomer of the Al13-Keggin structure as its structural motif. The new model is unrealistic because: (1) it is completely periodic (i.e. defect-free); (2), it has 20% tetravalent octahedral iron (VIFe4+), 20% divalent tetrahedral iron (IVFe2+), and some IVFe–O distances equal to or larger than the VIFe3+–O distances, thus violating Pauling's 2nd rule; (3) it does not describe X-ray diffraction and EXAFS spectroscopic data; and, (4) it is inconsistent with electron microscopy results and contradicts previous X-ray scattering studies.

Melt blending using a twin-screw extruder was used to prepare composites of polypropylene (PP)/organic rectorite (PR). The organic rectorite (OREC) was modified with dodecyl benzyl dimethyl ammonium bromide (1227). Wide-angle X-ray diffraction (WAXD) and transmission electron microscopy were used to investigate the dispersion of OREC in the composites. The d spacings of OREC in PR composites was greater than in OREC itself. The dispersion of OREC particles in the PP polymer matrix was fine and uniform when the clay content was small (2 wt.%). The rheology was characterized using a capillary rheometer. The processing behaviour of the PR system improved as the amount of OREC added increased. Non-isothermal crystallization kinetics were analysed using differential scanning calorimetry. It was shown that the addition of OREC had a heterogeneous nucleation effect on PP, and can accelerate the crystallization. However, only when fine dispersion was achieved, and at lower rates of temperature decrease, was the crystallinity greater. Wide-angle X-ray diffraction and polarized light microscopy were used to observe the crystalline form and crystallite size. The PP in the PR composites exhibited an a-monoclinic crystal form, as in pure PP, and in both cases a spherulite structure was observed. However, the smaller spherulite size in the PR systems indicated that addition of OREC can reduce the crystal size significantly, which might improve the ‘toughness’ of the PP. The mechanical properties (tensile and impact strength) improved when the amount of OREC added was appropriate. Dynamic mechanical analysis showed that the storage modulus (E′) and loss modulus (E″) of the nanocomposites were somewhat greater than those of pure PP when an appropriate amount of OREC was added. Finally, thermogravimetric analysis showed that the PR systems exhibited a greater thermal stability than was seen with pure PP.

The clay mineralogy and chemical composition of the white veins, red matrix and both Fe- and Mn-bearing nodules occurring in a laterite profile in Hubei, south China were investigated using X-ray diffraction, scanning electron microscopy equipped with an energy-dispersive spectrometer, and high-resolution transmission electron microscopy. The results show that the mineral components of the red matrix are mainly quartz, kaolinite, halloysite, goethite and minor illite, whereas the white net-like veins contain mostly quartz, kaolinite, halloysite, and illite. In the net-like horizon, the chemical index of alteration (CIA, the ratio of Al2O3/(Al2O3+CaO+K2O+Na2O)) and the TiO2/Al2O3 ratio are 89.8% and 0.021 for the white vein and 90.7% and 0.025 for the red matrix, respectively. Both white-vein and red-matrix components have similar TiO2/Al2O3 ratios, and are similar to the ratio 0.027 of the unaltered bedrock. The similarity in TiO2/Al2O3 values indicates that all three portions of the laterite soil share the same origin. Also, although the white-vein and red-matrix components differ in Fe2O3 abundance, the similar CIA values do imply similar degrees of alteration. The Fe-bearing and Mn-bearing nodules were produced by the local accumulation of Fe2O3 and MnO, respectively. Halloysite in the weathering profile occurs in two different morphologies, tubular and platy crystals. Tubular halloysite occurs both in the red matrix and the Fe-bearing nodule whereas platy halloysite occurs only in the white vein and Mn-bearing nodule assemblages. Crystallization of small tubular halloysite from Si and Al concretions in the red matrix is observed, indicating that the morphology of these crystals in the weathering environment is mainly controlled by Fe3+ cations, whereas platy halloysite may be derived from the hydration of kaolinite.

Alteration minerals dickite and kaolinite were detected in two hydrothermal Pb-Zn-Ag sulphide deposits in the northern Kosovo region. Dickite is associated with skarn mineralization in the Trepča (Stari Trg) deposit and kaolinite occurs in vein sulphide parageneses in the Crnac deposit. The mineralogical characteristics of dickite and kaolinite were determined by X-ray powder diffraction, Raman spectroscopy and scanning electron microscopy with EDS detector. Fluid-inclusion microthermometry and ion chromatography of leachates provided information on the P-T-X conditions of the genesis of dickite at Trepča. It was formed at temperatures between 290 and 330ºC and pressures between 12 and 60 MPa from a fluid with salinity in the range 6–8.5 wt.% NaCl eq. and pH <5.5. Kaolinite was deposited from a fluid with minimum temperatures between 210 and 250ºC, minimum pressure of 1.7 to 3.7 MPa, and salinity between 4.6 and 5.1 wt.% NaCl eq. Both dickite and kaolinite are related to the acidic pre-mineralization phase in the deposits.

The conductivity of La-montmorillonite was measured in the domain of water relative pressures (p/p0) of <1, and compared with the conductivites of Li- and Na-montmorillonite. La-montmorillonite shows smaller conductivity over the whole range of p/p0 studied. To explain this, theoretical considerations of the polarizing power and of the local stacking order induced by the exchangeable cation were addressed.

The Taşoluk kaolinite deposits of Afyonkarahisar (western Anatolia) are hosted by both pre-Early Cambrian sericitic mica-chlorite schists and Neogene volcanites, the latter comprising tuffs and agglomerates. These units have been affected by hydrothermal alteration controlled by faults resulting in complex, irregular, lateral mineralogical zonation. The occurrence of a siliceous cap on altered schists and in claystone, of quartz veins in schists and tuffs, and the development of explosion cones and pit fillings indicate that alteration in both the schists and the volcanites is due to hydrothermal processes. Altered schists have generally large (locally small) Fe contents, and claystones are generally silicified and have small Fe contents. Kaolinite predominates south and west of Taşoluk, whereas high (Fe+Ti)-bearing illite + kaolinite predominate in other altered sections. The kaolinite exhibits a stacked micromorphology within altered schists, and the altered volcanites record in situ precipitation, derived from a mechanism of paired dissolution and precipitation. Illite fibres coexist with kaolinite, smectite, chlorite, mica and sericitized feldspar in markedly altered schists, revealing that the illite formed either authigenically or by conversion of smectite to illite. A relative increase in Cr+Ni and decrease in Sr+Ba in the kaolinite deposits and their schistose host rock relative to the upper level of the kaolinite deposits and their volcanic parent rocks came about by the alteration of chlorite, mica and feldspar in the sericitic mica-chlorite schists, and feldspar, glass shards and schist fragments in the volcanites as a result of extensive faulting, fracturing and hydrothermal activity during Late Miocene-Pliocene volcanism, which contributed to the development of kaolinite deposits under acidic environmental conditions. With regard to industrial applications, the low-Fe kaolinized schists are suitable for use in refractories and paper coatings, while the claystone is suitable for use in ceramics and in the white-cement industry.

Acid mine-drainage from an abandoned Cu-S mine adit, located in the Avoca–Avonmore catchment in the southeast of Ireland, results in low-value ochre deposition. Ochre found on-site had similar physical (particle size 97.7% <2 mm and dry bulk density 0.8 g cm3), but dissimilar maximum P-retention characteristics (16–21 g P kg–1) to coal-mining ochre found in the UK. Stereomicroscopy identified oolites and diatoms in the ochre that were indicative of acidic environments. X-ray diffraction showed Fe mineralogy consisting of goethite, jarosite and minor amounts of ferrihydrite. Investigations by inductively coupled plasma-mass spectrometry and bulk energy-dispersive spectroscopy showed potentially toxic concentrations of Fe, Zn, Pb, As and Cu. Rapid mobilization of metals occurred during P-adsorption tests, which makes Avoca ochre unsuitable for use in a surface-water environmental technology.

L-cysteine (Cys) was adsorbed by bentonite (Ben) from aqueous solutions of variable concentrations and pHs. The raw materials and the adsorbed molecules (Ben-Cys) were characterized using X-ray diffraction (XRD), infrared spectroscopy (IR), thermal analysis methods (TG, DTG and DSC). The results indicated that the adsorption process depended strongly on pH, temperature and concentration of amino acid. Cysteine is specifically adsorbed on bentonite surface sites, probably through its NH3+ moiety. The pH dependence suggests that these sites may be silanolate groups (≡Si-O–). It is presumed that ion exchange interaction governs the adsorption process. The experimental data of adsorption isotherms obtained and analysed with the Langmuir model showed that this model fitted the adsorption data. Calculated thermodynamic parameters (ΔHº, ΔSº, and ΔGº) indicate that the adsorption processes were exothermic.

The literature on the formation, structure and properties of allophane and imogolite is reviewed, with particular emphasis on the seminal contributions by Colin Farmer. Allophane and imogolite occur not only in volcanic-ash soils but also in other environments. The conditions required for the precipitation of allophane and imogolite are discussed. These include pH, availability of Al and Si, rainfall, leaching regime, and reactions with organic matter. Because of their excellent water storage and physical properties, allophanic soils can accumulate large amounts of biomass. In areas of high rainfall, these soils often occur under rain forest, and the soil organic matter derived from the forest biomass is stabilized by allophane and aluminium ions. Thus the turnover of soil organicmatter in allophanicsoils is slower than that in non-allophanicsoils. The organic matter appears to be derived from the microbial by-products of the plant material rather than from the plant material itself. The growth of young forests may be limited by nitrogen supply but growth of older forests tends to be P limited. Phosphorus is recycled through both inorganic and organic pathways, but it is also strongly sorbed by Al compounds including allophane. When crops are grown in allophanic soils, large amounts of labile P are required and, accordingly, these soils have to be managed to counteract the large P sorption capacity of allophane and other Al compounds, and to ensure an adequate supply of labile P. Because of their physical and chemical properties, allophanic soils are excellent filters of heavy metals and pathogens.

Kogure and co-workers have published several papers reporting the stacking structures of various 2:1 layer phyllosilicates (e.g. aspidolite, Kogure et al. (2004); wonesite, Kogure et al. (2005); pyrophyllite, Kogure et al. (2006)), mainly by using high-resolution transmission electron microscopy (HR-TEM). However, there is ambiguity in wording that refers to the lateral displacement between two tetrahedral sheets across the interlayer regions. Zvyagin et al. (1969) used the symbol “τ” for this displacement, which describes the structures of pyrophyllite and talc, but no universally accepted wording was used for other 2:1 phyllosilicates or 1:1 phyllosilicates.