Clay Minerals
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The occurrence of palygorskite in Quaternary sediments of the coastal plain of north-west Egypt Abstract Sediments from a Quaternary beach ridge complex along the coastal plain of north-west Egypt have been examined by X-ray diffraction and optical and scanning electron microscopy. Palygorskite was identified in the caliche capping the beach ridges and in the gypsiferous marls between the ridges; petrographic evidence indicated that this had formed authigenically in both environments. Examples are thus provided of the pedogenic and evaporative in situ formation of palygorskite.
Clay Minerals - Tập 15 Số 1 - Trang 77-83 - 1980
Source of Palygorskite in Gypsiferous Aridisols and Associated Sediments from Central Iran
Clay Minerals - Tập 33 Số 4 - Trang 561-578 - 1998
The Experimental Chemical Weathering of Silicates
Clay Minerals - Tập 4 Số 26 - Trang 249-265 - 1961
The origin and formation of clay minerals in soils: past, present and future perspectives Abstract The origin and formation of soil clay minerals, namely micas, vermiculites, smectites, chlorites and interlayered minerals, interstratified minerals and kaolin minerals, are broadly reviewed in the context of research over the past half century. In particular, the pioneer overviews of Millot, Pedro and Duchaufour in France and of Jackson in the USA, are considered in the light of selected examples from the huge volume of work that has since taken place on this topic. It is concluded that these early overviews may still be regarded as being generally valid, although it may be that too much emphasis has been placed upon transformation mechanisms and not enough upon neoformation processes. This review also highlights some of the many problems pertaining to the origin and formation of soil clays that remain to be resolved.
Clay Minerals - Tập 34 Số 1 - Trang 7-25 - 1999
Grafted organic derivatives of kaolinite: I. Synthesis, chemical and rheological characterization Abstract Several new interlayer-grafted derivatives of kaolinite were synthesized by esterification of inner-surface hydroxyl groups with alkanols, diols and glycol mono-ethers starting with the dimethyl sulphoxide intercalate. The derivatives were characterized by X-ray powder diffractometry, thermal analysis, Fourier transform infrared spectroscopy and transmission electron microscopy. The grafted molecules are arranged in monolayers between the kaolinite layers, with typical basal spacings of ~11.3 Å. Rheological studies of aqueous dispersions of the modified kaolinites revealed an exponential increase of the yield value and apparent viscosity with increasing alkyl chain length of the grafted molecules.
Clay Minerals - Tập 40 Số 4 - Trang 537-546 - 2005
ESR and IR Evidence for Chromium in Kaolinites Abstract Evidence obtained from ESR and IR studies is presented for the presence of structural Cr in two natural kaolinites (MILO and GEY) formed in an hydrothermal environment in Sonoma County, California. The XRD patterns show a greater structural disorder for GEY than for MILO, but both have the usual hexagonal shapes as shown by TEM observations. On the basis of EDX analysis of different particles, GEY, on average, appears to be richer in Cr (2.1% Cr2 03 ) than MILO (0.6% Cr2 03 ). The presence of Fe oxide particles containing some Cr, Ni and V is also indicated by EDX analysis. By FT-IR observation, the octahedral Cr3+ position was easily detected by a well resolved spectral feature at 3586 cm-1 . The adsorbed Cr3+ kaolinite (KMRXCR) presents no band at 3586 cm-1 , but two other bands situated at 3527 and 3477 cm-1 . The main features of the ESR spectra of these two kaolinites are a set of resonances nearg eff 4; a broad resonance centred nearg eff 2 with some modulations; and a set of resonances near gcffl. The broad resonance centred nearg eff 2 is interpreted as the free iron oxide signal with modulations due to VO2+ . The set of resonances nearg eff 4 is similar to that observed for octahedral Fe3+ , but the position is shifted compared to that of octahedral Fe 3+. This set of resonances nearg eff 4 is, therefore, interpreted as belonging to Cr3+ in octahedral position. The resonances atg eff 1 are also interpreted as belonging to Cr3- . Comparison with the Cr3+ surface-adsorbed ESR signal of a Cr-saturated kaolinite (which is a broad resonance centred nearg eff 2) strengthens the interpretation of theg eff 4 resonances belonging to Cr3+ in the octahedral position. The results obtained by the combination of FT-IR and ESR spectroscopics indicate that Cr3+ is present in the octahedral position of the MILO and GEY kaolinites.
Clay Minerals - Tập 28 Số 3 - Trang 353-364 - 1993
Order-disorder in clay mineral structures Abstract Some recent works dealing with the concept of order-disorder in clay minerals are considered, including those aspects of order-disorder which appeared in the Brindley & Brown (1980) monograph, i.e. disorder in the distribution of cations, disorder in layer stacking, orderdisorder in mixed-layer systems and finite crystal size as a lattice disorder. Heterogeneity of samples and polymorphous transformations are also considered as other types of disorder. Most of these works emphasize that accurate structural characterization can only be obtained if several techniques are combined (e.g. XRD and IR, EXAFS and Mo¨ssbauer spectroscopies, etc.). Another conclusion is that accurate structural determination provides the key to the genesis of clays.
Clay Minerals - Tập 36 Số 1 - Trang 1-14 - 2001
New data on the kaolinite-potassium acetate complex Abstract The intercalation complex of kaolinite and potassium acetate (KAc) was studied by HTXRD, IR spectroscopy and DTA-TG. The HTXRD patterns indicate that the 14.06 Å basal spacing of the complex contracts to 11.77 Å and 9.35 Å after heating at 60°C. The DTA-TG data indicate that water is present in these new complexes, the decomposition of which occurs between 290°C and 400°C. Modifications observed in the high-frequency region of the spectra obtained after heating suggest that K ions occupy the ditrigonal holes in the OH surface of the kaolinite layers, whereas water is probably located between the KAc layer and the OH surface of the kaolinite. This structural arrangement would favour the H-bonding between inner-surface OH groups and water and justifies the presence of new bands at lower frequencies. Electrostatic interactions between the keyed K ions and O of the inner OH groups would justify the modifications of the 3619 cm-1 OH-stretching band.
Clay Minerals - Tập 34 Số 4 - Trang 565-577 - 1999
Aluminium coordination and structural disorder in halloysite and kaolinite by <sup>27</sup>Al NMR spectroscopy Abstract It has been suggested that interlayer water in halloysite is due to the presence of hydrated cations that balance the negative layer charge produced by Al for Si substitution. To find evidence of 4-coordinate Al (Al(IV)), we investigated six halloysites and two kaolinites using ‘high-field’ and ‘medium-field’ solid-state 27 Al MAS NMR spectroscopy. We found Al(IV) in both kaolinite and five halloysite samples, but the contents are all <1% and provide no basis for distinguishing between kaolinite and halloysite. Therefore, the presence of interlayer water in halloysite cannot be attributed to Al for Si substitution. There are, however, signals, tentatively assigned to A1(V), present in the kaolinite spectra but not in the halloysite spectra. The shapes of the low-frequency ‘tails’ of Al(VI) signals in medium-field NMR vary from sample to sample. We interpret this variation in terms of a ‘crystallinity index’. Disorder in kaolinite appears to be primarily the result of Al-vacancy displacements in the octahedral sheet. The NMR crystallinity indices correlate with those from IRS and DTA but not with those from XRD.
Clay Minerals - Tập 29 Số 3 - Trang 305-312 - 1994
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