Bangladesh has been divided into 30 Agroecological Regions (AEZs) and the applied agricultural research has currently been conducted on this basis. In context of the lack of enough mineralogical information on the AEZ basis, an attempt has been taken to study mineralogy of important soils from all AEZs of Bangladesh in order to provide basic information for applied research. As a part of this attempt, the mineralogy of ten soils from the Lower Atrai Basin (AEZ 5) and six soils from the Lower Purnabhaba Floodplain (AEZ 6) has been reported in this paper. The soils of both AEZs were acidic in nature, had moderate to high amounts of clay, and the texture was medium (silt loam) to heavy (clay). The 2-20μm silt fraction of the soils having more than 25% of clay (Laskara-1, Laskara-2, Tarash-1 and Tarash-2 soils of AEZ 5 and all soils of AEZ 6) was composed mainly of quartz, with small amounts of mica, plagioclase, K-feldspar and chlorite, while other six soils of AEZ 5 (having less than 25% of clay) had relatively lower amounts of quartz (but still dominant) with fairly good amounts of mica, chlorite and plagioclase and low amounts of K-feldspar. Similarly, the <2μm clay fraction wasd ominated by mica along with interstratified kaolinite-smectite and mica-vermiculite-smectite minerals in the former group of soils having the higher clay content while with vermiculite in the latter group of soils having the lower clay content. The impact of mineralogy on the genesis and classification of soils in AEZs 5 and 6 has been discussed.

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Adsorption of water is a one of important physicochemical properties of clays, and allophane has extremely high water adsorption capacity due to its high specific surface. The water vapor adsorption of two allophane samples with low and high Si/Al ratios (0.67: KyP; 0.99: KnP), under various relative humidities (RHs), decreased with preheating treatment up to 400°C for 2h. The decrease in water adsorption at monolayer level (RH=0.45) was greater for KnP sample than for KyP sample, whereas the decrease in water adsorption due to capillary condensation between allophane unit particles (RH=0.6) was greater for KyP sample. These indicate that allophane hollow spheric particles in KyP sample were directly connected each other with the preheating, but those in KnP sample were not. The difference in the way of bonding between unit particles in the two types of allophane was ascribed to the presence of polymerized silicate ‘tails’ exposed outside of hollow spheric allophane particles. In the KnP with higher Si/Al ratio, many ‘tails’ are exposed, and the ‘tails’ might prevented direct attachment between particles by forming connection between the ‘tails’. The presence of the ‘tails’ in allophane with higher Si/Al ratio was also related to dispersion property of allophane of this type.

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Characteristics of clay-humus complexes in mangrove surface soils along a mangrove creek in Fukido river, Ishigaki island, Okinawa were investigated under this study. Six locations from the lower site to upper site in the river were selected, and surface soils (0.5cm thick) were collected at two different sides of the bank and the forest. The degree of humification of NaOH soluble (NaOH-HA) and Na₄P₂O₇soluble (Na₄P₂O₇-HA) humic acids of mangrove surface soils were Rp and B types, respectivTh e degree of humification of humic acids was gradual degradation from upper to lower sites in the mangrove forest. Humic substances were accumulated in larger quantities in surface soils while are closer to waterside of the bank and were tended to sediment in larger quantities at about 220m from downstream in the mangrove forest. Contents of clay minerals (Kaolinite, Illite, Vermiculite and Vermiculite-Chlorite integrade), extracted bases (Na, K, Mg and Ca) and metals (Fe and Al) in humic substances showed a similar accumulating tendency to the humic substances.
It can be concluded that the clay-humus complexes were formed with clay minerals, metals and basesi n mangrove surface soils. It was apparent the complexes were accumulated in mangrove surface soils, based on the characteristics of the topography.

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Cathodoluminescence (CL) measurements of clay minerals were performed at both room temperature and low temperature. Panchromatic CL images of kaolinite and dickite show blue emission at room temperature. Their CL spectra exhibit an intense broad band peak at around 375nm. This emission band related to radiation induced defect centers (RID) disappears at low temperature. Effect of sample temperature on CL intensity of kaolinite and dickite can not be interpreted on the basis of a temperature quenching theory. In halloysite, serpentine minerals, sericite and sepiolite, the intensity of a broad band between 400 and 450nm is higher at low temperature than at room temperature. CL spectra of serpentine minerals are characterized by a broad band centered at 720nm, which can be assigned to Fe³⁺ impurity center.
Natural TL glow curve of sepiolite presents two glow peaks around at 210 and 260°C in the high temperature region, of which intensities are weak. This implies that it is rather a possibility of applying TL of sepiolite to the dating. The other minerals show no emission in natural TL measurements. X-ray induced TL of kaolin minerals exhibit intense several TL glow peaks below room temperature. Serpentine minerals have glow curves with a relative large peak between 70 and 90°C. Sericite, montmorillonite and sepiolite show a combination of emission peaks in their TL glow curves, while their intensities are weak compared to kaolin and serpentine minerals. Clay minerals might have characteristic TL related to their crystal structure.

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We synthesized a nano-scale aluminum germanate tubular material with a similar structure of clay mineral imogolite. This nano-tubular material can be obtained from a concentratedinorganic solution using GeO₂ dissolved in NaOH as the source of germanium. The IR spectrum, powder X-ray diffraction profile and TEM image are similar to those of previously reported aluminum germanate tubular material prepared using GeCl₄. Tapping mode atomic force microscopy revealed that our novel material had tubes which were shorter in length and wider in diameter than those of synthetic imogolite.

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