D. Papoulis

PROGRESSIVE STAGES IN THE FORMATION OF KAOLIN MINERALS OF DIFFERENT MORPHOLOGIES IN THE WEATHERING OF PLAGIOCLASE

Halloysite and kaolinite occur in gneissic weathering profiles developed under a temperate climate in the Leucogia area of NE Greece. X-ray diffraction analyses of samples from three profiles of partially weathered gneisses have revealed that kaolinite becomes more abundant than halloysite with increasing intensity of the decomposition processes. To resolve the genetic relationship between halloysite and kaolinite, microtextures were examined by scanning electron microscopy using polished thin-sections and freshly exposed fracture surfaces, and their chemical compositions were determined using an analytical scanning electron microscope fitted with energy dispersive and wavelength dispersive spectrometers. Different morphological forms of halloysite and kaolinite were detected within the same rock mass. In the earliest stage of weathering, spheroidal aggregates consisting of microcrystalline halloysite are formed on the plagioclase surface. With progressive weathering, spheroidal halloysite converts to tubular halloysite. As weathering advances, tubular halloysite converts to platy halloysite, which in turn converts to kaolinite. Halloysite and kaolinite may coexist in the upper parts of the profiles. Electron microprobe analyses of spheroidal, tubular and platy halloysite and kaolinite show that the chemical composition of the various forms indicate a progressive Fe enrichment and Al depletion with advancing kaolinization, from VIFe0.08VIAl3.70 a.p.f.u. in spheroidal halloysite through VIFe0.29VIAl3.50in platy halloysite to VIFe0.53VIAl3.32 in newly formed kaolinite. Final-stage, book-type kaolinite approaches its ideal chemical composition (VIFe0.04VIAl3.95). The mineralogy and composition of the kaolin minerals and the development of the various morphological forms of halloysite and kaolinite in different parts of the profiles are attributed to the chemistry of the ambient solutions. However, other physical and microenvironmental conditions (e.g. time and space available) also seem to have strong influence on the precipitation processes producing the morphological variations.

Attachment of Pseudomonas putida onto differently structured kaolinite minerals: a combined ATR-FTIR and 1H NMR study.

The attachment of Pseudomonas (P.) putida onto well (KGa-1) and poorly (KGa-2) crystallized kaolinite was investigated in this study. Batch experiments were carried out to determine the attachment isotherms of P. putida onto both types of kaolinite particles. The attachment process of P. putida onto KGa-1 and KGa-2 was adequately described by a Langmuir isotherm. Attenuated Total Reflection Fourier Transform Infrared Spectroscopy and Nuclear Magnetic Resonance were employed to study the attachment mechanisms of P. putida. Experimental results indicated that KGa-2 presented higher affinity and attachment capacity than KGa-1. It was shown that electrostatic interactions and clay mineral structural disorders can influence the attachment capacity of clay mineral particles.

Geochemistry of halloysite-7Å formation from plagioclase in trachyandesite rocks from Limnos Island, Greece

Abstract Trachyandesite rocks, occurring over an area of about 1 km2 in the southwest part of Limnos Island, Greece, are altered mainly to halloysite. The samples were collected and analysed by polarizing microscopy, powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and chemical analysis. The alteration of plagioclase to halloysite follows seven discrete stages that are described in detail. The geochemical evaluation of the data shows enrichment of the light REE (LREE) over heavy REE (HREE) as expressed by the (La/Yb)n ratio. The ΣLREE range from 206.44 to 272.30, while the sum of HREE varies from 11.01 to 26.26. The (La/Yb)n ratio ranges from 9.72 to 27.64. Fractionation among ΣLREE expressed as (La/Sm)n and between middle REE (MREE) and HREE is shown as (Tb/Yb)n ratios. The most altered rocks close to the fault zone have high (Tb/Yb)n ratios and low (La/Sm)n and Eu/Eu* ratios. Although mineralogy and clay mineral textures indicate hydrothermal genesis of halloysite, the geochemical data are not conclusive due to a secondary weathering effect.

Clay‐based Nanocomposites Possibilities and Limitations

In the last decades, clay mineral based nanocomposites and polymer–clay nanocomposites (PCNC) have been proposed as very useful materials for many uses including photocatalysis, medicinal uses as tissue engineering or modified drug delivery systems. Clay minerals and especially montmorillonite, kaolinite, halloysite palygorskite and sepiolite are the most used clay minerals because of their high surface areas, colloidal dimensions of their particles and other properties. This lecture aims at reporting on very recent developments in the use of clay minerals and PCNC as materials with photocatalytic and medical interest.

An FT-Raman, Raman and FTIR study of hydrothermally altered volcanic rocks from Kos Island (Southeastern Aegean, Greece)

Abstract Both Tertiary and Quaternary volcanic rocks occur in Kos Island. The Quaternary volcanism produced a successive series of rhyolitic-dacitic volcanic rocks both lavas and pyroclastics. Hydrothermal alteration of rhyolitic rocks at Kefalos peninsula (at southern tip of the island) and Asfendiou (NE Kos) resulted in kaolin formations. At both places, alteration is clearly associated with faults. The mineralogical study of the kaolin samples was carried out using various vibrational spectroscopic techniques, covering a broad wavenumber range (Raman, FT-Raman and FTIR) along with XRD and SEM analytical methods. The study of the kaolin samples showed that mixed-layer kaolinite-smectite developed from the alteration of K-feldspar, while the pure kaolinite from both Kefalos and Asfendiou areas, is the result of Na-plagioclase alteration. Book-type dickite forms after kaolinite and represents peak conditions of hydrothermal alteration. The presence of zunyite, a rare mineral that occurs in hydrothermal alteration regimes, has been verified in the kaolin samples from both areas. The assemblage kaolinite + dickite + zunyite ± pyrophyllite, in the most altered samples, is stable at a temperature range between 250°C and 290°C, at low pH (