Texture and mineralogical composition of Quaternary terrestrial and marine sediments from Macedonia and Thrace, Greece

Clastic sediments collected from land and gulfs of Macedonia and Thrace in Greece are examined on the basis of their texture and mineral composition. All terrestrial samples are coarse-grained and poorly sorted, with angular to sub-angular grains. These are mainly composed of quartz and feldspars, followed by micas, calcite and Fe-Mg minerals. Among the clay minerals illite predominates over smectite and smectite over vermiculite (+chlorite+kaolinite). In addition, the interstratified phases illite/smectite, chlorite/vermiculite, and smectite/vermiculite are present in significant amounts in the clay fraction (<2 μm), signifying the incomplete weathering of the primary minerals. Mixing during transportation, flocculation, differential settling processes and organic matter are the main mechanisms for the distribution of the discharged terrigenous load into the North Aegean Gulfs. All gulf bottom samples are coarse to fine grained and medium sorted, and their grains are angular to sub-angular. Quartz and feldspars predominate. In addition, biogenic calcite, micas and various Fe-Mg minerals exist as primary and/or accessory minerals. Among clay minerals, illite predominates over smectite and smectite over kaolinite (+chlorite+vermiculite). Almost in all gulf sediments the interstratified phase illite/smectite is apparent. The presence of feldspars and Fe-Mg minerals, as well as the high content of clay minerals and the polymodal grain-size distribution with angular to sub-angular grains, signify mineralogical and textural immaturity of all the examined sediments, as well as predominance of mild climatic conditions and thus mild weathering processes. The quartz content in these sediments is usually <70%. Therefore, a sedimentation cycle of these materials has not been completed.

Grain size distribution, clay mineralogy and chemistry of bottom sediments from the outer Thermaikos Gulf, Aegean Sea, Greece

The Thermaikos Gulf constitutes the NW part of the North Aegean Sea and is limited eastward from the Chalkidiki Peninsula and westward from the Pieria Prefecture. Its plateau covers an area of 3,500 km2. The mechanisms responsible for the grain size distribution into the Gulf, the clay mineralogy and the chemistry of some bottom sediments from the outer Thermaikos Gulf, are examined. Source mixing during transportation, flocculation, differential settling processes and organic matter appear to be the main mechanisms for the distribution of clay minerals in shallow waters. All grain size fractions studied present a wide range of values confirming the extreme variations of the discharged load and the variability in marine processes. Plagioclases predominate over K-feldspars, while quartz is the most abundant mineral present. In addition, micas, chlorites, amphiboles and pyroxenes exist as primary and/or accessory minerals in all samples. Among clay minerals, illite predominates over smectite and smectite over chlorite (+ kaolinite). The ordered interstratified phase of I/S, with 30-35% S layers, is present in the 2-0.25µm fraction. The randomly interstratified phase of I/S, with 50% S layers, is present in the <0.25& micro; m fraction. On average the clay mineral content of the studied samples is: 48% I, 23% S, 17% Ch (+K) and 12% others for the 2-0.25µm fraction and 50% I, 30% S and 20% Ch (+K) for the <0.25 µm fraction. All these minerals are the weathering products of the rocks from the drainage basins of the rivers flowing into the Gulf, as well as of the Neogene and Quaternary unconsolidated sediments of the surrounding coasts. The terrigenous input, the water mass circulation and, to a lesser extent, the quality of the discharged material and the differential settling of grains, control the grain size distribution within the outer Thermaikos Gulf. The chemical composition of the analysed samples is generally in agreement with their mineral composition and signifies their terrigenous origin presenting discretely clastic character.

Study of the dehydration process of vermiculites by applying a vacuum pressure: formation of interstratified phases

Structural transformations between the different hydration states of three vermiculite samples from Sta. Olalla (Huelva, Spain), Paulistana (Piaui, Brasil) and West China, have been observed by X-ray diffraction at atmospheric pressure, P = 1.4 x 10–2 mbar and P = 2.4 x 10–4 mbar. The samples were studied in flake and powder forms. The effect of vacuum has been proven to be the same as that of temperature, i.e. it causes dehydration of vermiculite, but with a different evolution through the different hydration states. In fact, under vacuum, the process seems to be inhibited at a one-water layer hydration state (1-WLHS), without a further dehydration of samples to a zero-water layer hydration state (0-WLHS).Furthermore, the dehydration process has been shown to occur through different interstratified states in each vermiculite. This result has been related to the interlayer Mg-cation content, due to its affinity to water molecules. The interstratified states have been analysed by the direct Fourier-transform method. The vermiculite from Sta. Olalla exhibits the most complex process, with formation of three different interstratified phases: two phases characterized by an interstratification of interplanar distances, d = 11.5 –13.8 Å and d = 9.6 –11.5 Å , respectively, and a practically segregated phase characterized by d = 13.8 Å . For the vermiculite from China, an interstratified phase not previously reported has been found, with an interplanar distance of 12.10 Å.The inhibition of dehydration at 1-WLHS, as observed, could be used in applications such as adsorption and separation technology of gases and liquids, or in heterogeneous catalysis processes.

Nature of interstratified kaolin-smectites in some Australian soils

The clay minerals in the < 2 �m, and finer, size fractions of several horizons from each of five Australian soils of different types and from different locations have been analysed by X-ray diffraction, infrared spectroscopy, transmission electron microscopy and X-ray fluorescence. Samples from each profile contained a phase in which layers of smectite and of kaolin (positively identified as kaolinite) were randomly interstratified with each other. The relative proportions of the two types of layers varied widely. One interstratified phase contained 70% smectite. This value for smectite content of kaolin-smectites is as high as any reported in the literature. The charges associated with the interstratified smectite layers also differed substantially. Discrete kaolinite commonly occurred along with interstratified kaolinite-smectite, Towards the surfaces of the soils, the proportions of kaolinite in the interstratified phases increased at the expense of smectite.