Different forms of structural and chemical heterogeneity are considered including mixed-layer minerals, disordered layer structures containing rotational and translational stacking faults, interstratification of trans-vacant (tv) and cis-vacant (cv) layers in true micas, illites and illitesmectite (I-S), short-range order in isomorphous cation distribution etc.

Because determination of various structural and chemical imperfections requires elaboration of new diffraction and spectroscopic methodologies, special attention is paid to recent achievements in the development of new methodological approaches such as a multispecimen simulation of experimental X-ray diffraction (XRD) patterns from mixed-layer minerals, with account taken of layer-thickness fluctuations of the second type and possible difference between structures of outer and core layers; experimental determination of thickness distribution of illite crystals by HRTEMand the modified Bertaut-Warren-Averbach technique; XRD and thermal methods for determination of cv and tv layers in true micas, illites and I-S; generalization of Méring's rules to account for the behaviour of non-basal reflections for any defective structure in which two translations are irregularly interstratified; various ab initio calculations devoted to modelling infrared OH vibrations, octahedral cation distribution in dioctahedral 2:1 layer silicates, etc. It is shown that these recentlydeveloped methodologies have revealed new diversity in the structural and chemical heterogeneity of phyllosilicates and clay minerals, provided new insight into the structural mechanisms of their transformation in different geological environments, and discovered new natural processes.

The mechanisms governing the adsorption of a commercial humic acid (HA) on a kaolinitic clay were determined. The amount of HA fixed increased with the ionic strength of the medium and the presence of divalent ions (Ca2+). The effect of Ca2+ is due to its ability to establish (1) intramolecular bridges causing condensation of the HA, and (2) intermolecular bridges between the clay and the HA. A stable clay-humic complex containing only the fraction of HA that withstands washing with water was prepared and characterized by high-resolution Ar adsorption volumetry. The overall results show that (1) HA interacts strongly with the basal surfaces of the clay, (2) Ca serves to establish Ca2+ bridges between HA and clay, and (3) HA and clay interact via at least two distinct adsorption mechanisms.

The hydrothermal reaction of kaolinite in the system Na2O-K2O-MgO-Al2O3-SiO2- H2O-HCl, at near-neutral pH conditions, has been investigated at 200ºC, for times from 12 h to 180 days. X-ray diffraction (XRD) study of the solid products indicates that the phases formed from 15 days’ reaction time are randomly ordered mixed-layer chlorite-smectite, dioctahedral on average, with a chlorite:smectite ratio of ∼1:2. No structural evolution was observed with increasing reaction time. Investigation by transmission electron microscopy revealed, on the contrary, that very thin packets with basal spacing of either 10 Å (smectite) or 14 Å (chlorite) are dominant. In addition, packets with periodicities of 12 –13 Å are also observed. Only rarely, randomly to ordered sequences of 10 and 14 Å are observed in the packets. These observations indicate that the mixture of these phases behaves in XRD as randomly ordered mixed-layer chlorite-smectite. Chemical analysis of the solutions suggests that the neo-formed phases are metastable and would evolve, at longer reaction times, toward ordered mixed-layer chlorite-smectite or to clinochlore.

The Puncoviscana Formation, largely cropping out in NW Argentina, is mainly composed of a pelite-greywacke turbidite sequence affected by incipient regional metamorphism and polyphase deformation. Metapelites, composed mainly of quartz, albite, dioctahedral mica and chlorite, were sampled in the Lules-Puncoviscana and Choromoro belts. Lattice-fringe images, selected area electron diffraction and analytical electron microscopy analyses, coupled with previous data from white mica crystallinity index, indicate a state of reaction progress for Puncoviscana slates consistent with medium anchizone- to epizone-grade metamorphism. The 2M polytype prevails in dioctahedral micas, coexisting in a few cases with the 1Md polytype as a consequence of lack of equilibrium. The 2Mpolytype coexists with 3T in two slates and long-range four-layer and ten-layer stacking sequences were identified in another sample. Samples with 3T and long-range stacking sequences present b values characteristic of intermediate–high pressure metamorphism and ordered chlorites (1L, 2L, 3L and 7L) prevail.

Based on the Si contents of dioctahedral micas and considering peak temperatures of ∼350 –400ºC, pressures from 5 kbar and 5 –7 kbar were derived for metapelites from the Lules- Puncoviscana and Choromoro belts, respectively. These values agree with facies series derived from the b values. Micas with a wide range of phengitic substitution, as evidenced by Fe + Mg and Si contents, coexist. These variations could not arise from the disturbing effect of detrital white K-mica because TEM evidence indicates that they are absent or represent <10% of the mica population. Thus, compositional variations suggest that dioctahedral micas of individual slates crystallized at different pressure conditions in response to the P-T path of the metamorphism. Moreover, in several biotite-free slates the illite crystallinity (IC) values lead to an underestimation of the metamorphic grade attained in these rocks.

The coexistence of IC corresponding to anchizone and the occurrence of biotite in some slates and felsic metavolcanic rocks intercalated in the Puncoviscana metasediments are interpreted to be the result of a metamorphic path including a relatively high-pressure/ low-temperature (HP/LT) event, followed by a lower-pressure overprint possibly at higher temperatures than the HP/LTevent. Small micas formed during the high-pressure stage would prevail in the <2 mm fraction, producing anchizone IC.

The adsorption of the anionic dye Congo Red (CR) by Na-, Cs-, Mg-, Cu-, Al- and Fe-montmorillonite was investigated by electronic spectroscopy. Spectra of the aqueous suspensions of different clay concentrations and different loadings were recorded. The spectra were curve fitted and were compared to spectra of aqueous solutions of CR at different pH values. Four bands representing anionic varieties and two representing protonated varieties of CR were identified in spectra of CR-treated Na-, Cs-, Mg-, Cu- and Al-montmorillonite. Spectra of CR-treated Femontmorillonite were slightly different, showing three bands representing anionic varieties and four representing protonated CR. The ratio between areas of bands, which represent the protonated varieties, and those representing the anionic varieties were determined showing correlation with the acidity of the metallic cation. The clay in the aqueous suspensions became coloured after the adsorption of CR. The following stainings were obtained, Na- and Mg-clay, red, Cs-clay, violet-red, Cu-clay, reddish-violet, Al-clay, dark violet and Fe-clay, dark blue. It appears that CR can serve as an indicator of the surface acidity of montmorillonite. The effects of aging on the sorption of the dye and on the surface-acidity of the CR-clay complex were investigated.

Four different types of natural clay were tested as potential adsorbents for toxic Pb2+ ions. Based on the preliminary screening studies, the adsorbents were effective at retaining Pb2+ ions from solution. A strong correlation was observed between the cation exchange capacity of clay samples and their function as adsorbents of Pb2+ ions. An adsorption isotherm of Pb ions on Petra clay was measured at 30ºC and at a concentration range of 0 –200 mg dm–3. Over the entire concentration range, the Langmuir isotherm gave a good representation of adsorption data, which confirms the formation of one molecular layer of adsorbate on the clay surface. Two variables were investigated to elucidate the rate-limiting steps of adsorption: the effect of initial concentration of Pb2+ and the effect of solution temperature. It is concluded that external diffusion was the only mechanism in operation in the adsorption process. It has been noted that adsorption of Pb2+ by natural clay is a fast process, where 80% of equilibrium capacity was established within the first minutes of interaction.

The clay mineralogy of soils and of the main calcareous sedimentary parent rocks of southern Iran were investigated to determine their origin and factors controlling their distribution pattern in soils. The results revealed that the soil-available moisture plays the major role in the distribution pattern of palygorskite and smectite clay minerals in the arid and semi-arid areas studied. There is an inverse correlation between palygorskite and smectite with regard to the soil-available moisture as expressed by P/ETº (ratio of mean annual precipitation to mean annual reference crop evapotranspiration). At P/ETº values >0.4 palygorskite transforms to smectite. Smectite is thought to be mainly of ‘transformed’ origin. It is detected in trace amounts in soils of more arid areas and increases in soils having greater available moisture. The general decrease in illite content with depth is related mainly to its transformation to smectite under favourable moisture conditions of the deeper horizons. Palygorskite is considered to be inherited in plateau soils of the arid regions whereas in saline and alkaline soils and soils with high gypsum, it is mainly of authigenic origin. The P/ETº and gypsum content show a significant correlation with the palygorskite content. The occurrence of kaolinite in some soils is due to its inheritance from the surrounding kaolinite-bearing Cretaceous rocks. Illite and chlorite abundance in soils is also largely related to their presence in parent rocks. The rare occurrence of vermiculite in the studied calcareous soils is mainly related to its lower stability under high pH, low Al activity and the presence of large amounts of Si and Mg in soils.

In the area of S° ile, NW Turkey, Upper Cretaceous calc-alkaline volcanic rocks with compositions ranging from andesite to rhyolite have been recognized. The most widespread rocks of the suite are andesites, which can be grouped into altered and fresh. The oldest altered andesites are the parent rocks for the kaolin deposits of the study area. The Upper Cretaceous volcanic suite consists of spilite, basalt, andesite, trachyandesite, trachyandesitic and hyaloandesitic dacite, rhyolite lavas, tuffs and agglomerates. The highly altered andesites are composed of plagioclase, pyroxene, hornblende, biotite, augite and very fine opaque minerals. During the Turonian, an E –W trending extensional magmatic arc was developed in the Istanbul Tectonic Zone of the oceanic Western Black Sea basin and intermediate volcanic rocks were emplaced, mostly calc-alkaline andesites, suggesting multi-stage magmatism. The significant features of the andesites are: (1) enrichment of LILE (Rb, Ba, K) over HFSE (Zr, Nb, Hf, Ti, Th, U, Y) and LREE (La –Sm), resulting in high Ba/Nb, Th/Nb, Ba/La, K/Ti and Th/La ratios; (2) depletion of LREE over HFSE, MREE and HREE, generating high La/Nb, Ce/Ti, La/Sm and La/Y values; and (3) depletion of Nb, Sr and Ti; all of which are typical of island arc magmatism, with possible back arc signature. The Th-Hf-Ta diagram for tectonomagmatic classification shows that the S° ile calc-alkaline rocks are similar to volcanic rocks from the Mariana Arc, the Aeolian Arc of Salina, Italy, the Skaros island in the Aegean Sea and Sardinia's ignimbrites. Moreover, relatively low La/Th and Ce/Pb ratios suggest that the source region of volcanism was enriched in LILE with respect to REE, indicating crustal contamination during melting.

Highly weathered andesitic rocks, rich in smectite, were transported gradually and deposited in a lacustrine basin, a coal-forming dysaerobic environment, in which they were subject to post-depositional alteration, or in situkaolinization, to form a kaolin deposit in the presence of humic and fulvic acids. The mobility of major and trace elements and REEs during the progressive kaolinization of andesitic materials has been investigated to reveal the geochemical characteristics of Upper Cretaceous volcanic parent rocks and to explain mineralogical processes in a kaolin deposit as a daughter rock ‘end-product’ . Alteration is characterized by the loss of Si, Fe, Ca, Na and K, and by the gain of Al, Ti, Zr and LOI. Moreover, Ho, Er and Yb are immobile, and Hf, Zr and Nb are mobile. Th and U are slightly enriched in clay horizons with respect to the andesitic rocks. In addition, Cr, Ga, Nb and Ta enrichments indicate variable sources of terrigenous sediments and differential mobilities of elements in lake waters rich in organic acids. The anatase concentration increases in the <2 mm size fractions as subspherical particles and these precipitate at acidic conditions (pH ≈ 5) during early diagenesis.

The thermal transformations of kaolinite have been studied using 27Al and 29Si magic angle spinning nuclear magnetic resonance (MAS NMR), X-ray diffraction (XRD), differential thermal analysis (DTA) and thermogravimetric analysis (TG). The experimental results show that this sample is a pure kaolinite which contains ∼3% carbonaceous material as impurity. 27Al and 29Si MAS NMR spectra show that the microstructural evolution of the thermal transformation of kaolinite at 450 –1050ºC is similar to that of the kaolinite– mullite reaction series previously published by many authors. 29Si MAS NMR spectra of mullite at 1190 and 1250ºC display two resonances at ∼ – 87 and –92 ppm, corresponding to sillimanite-type geometry around Si and the typical Si environment of mullite, respectively. At 1350ºC, the splitting of (hk0) and (kh0) of mullite occurs, indicating that the primary mullite transforms into orthorhombic mullite. Simultaneously, the resonance at ∼ – 92 ppm splits into two signals at ∼ –90 and –94 ppm. 27Al MAS NMR spectra of the mullite consist of three signals centred at ∼ –4, 45 and 60 ppm, corresponding to octahedral, distorted tetrahedral and tetrahedral Al sites, respectively.

Cationic dye, methylene blue (MB), was intercalated into films of expandable clay minerals with low, moderate and high layer charges (saponite, montmorillonite and synthetic expandable mica-fluorohectorite, respectively) . Tilted orientation of the dye cations on the silicate surface was observed by polarized ultraviolet-visible (UV-Vis) transmission spectroscopy. The tilting angle of the dye cations increased with the formation of high-order H-aggregates that absorb light at 525 nm. These dye species were formed only on the surface of fluorohectorite, which has the highest layer charge, and exhibited dichroism. Models for the orientation of MB cations on a clay surface were proposed based on MB orientation models previously reported, and compared with the basal spacings determined by X-ray diffraction.