X-ray diffraction experiment of a granular glauconitic clay and the computer simulation of the X-ray diffraction line profile of the clays from the Minamishiraoi Kuroko-type deposit, southwestern Hokkaido, Japan, were carried out to elucidate its mixed layer structure. The mixed layer structure which shows an intermediateproperty of glauconite and smectite were evaluated to be of a random-type interstratification somewhat deviated from random interstratification towards the direction of segregation structure of glauconite and smectite, through comparison of the measured and the calculated X-ray diffraction line profiles.
It is suggested that the comparisons of the relative intensity ratio of the saddle peak and the (001) reflection corresponding to smectite, and the X-ray diffraction pattern between the measured and calculated ones, can be used efficiently as one of the methods to evaluate the mixed layer structure of glauconite-smectite series mineral in the clay.

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The transformation of two natural siliceous ferrihydrites to hematite has been observed by X-ray diffraction, Moessbauer spectroscopy, weight loss and colour change. Three synthetic ferrihydrites (a 2-line pure sample, a 7-line Si-containing sample and a 7-line Ge-containing sample) have been used for comparison. The inhibitory effect of Si on the transformation, as observed previously, has been confirmed, and Ge has been found to exert a similar effect. Adsorption of soluble silicate onto the 2-line pure ferrihydrite also produced an inhibitory effect. It was possible to reduce OH: Fe ratios in ferrihydrites to the order of 1: 10 or less without an apparent phase change, and the essentiality of H₂O and OW in the ferrihydrite structure is questioned. The results are consistent with a model in which Si-or Ge-hydroxy anions are bonded to, and bridge, the surfaces of crystalline domains within each primary particle of ferrihydrite.

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Clay mineralogical compositions of calcareous and noncalcareous floodplain soils which are most widely distributed over Bangladesh were investigated.
The calcareous soils formed over the Gangese sediments are more alkaline having high extractable bases than the noncalcareous soils of the Bahmaputra sediments.
The compositions of clay minerals of both the soils were constituted mainly of 14, 10 and 7 Å components. Of them, mica was commonly observed abundantly with the smaller amounts of kaolinite, chlorite and the interstratified minerals of these components. Especially, the noncalcareous soil clays were dominated by mica.
The main characteristics for both the soil groups were observed in the 14 Å constituents, i.e. the calcareous soil clays were smectitic and the noncalcareous were vermiculitic. The noncalcareous soil clays were characterized by the absence or very low contents of smectite and the high contents of vermiculite, while, the calcareous clays always contained considerable amounts of smectite with a trace to moderate amounts of vermiculite. Moreover the relative high contents of hydroxy-Al interlayering components were existed in all clays and they were identified as Al-vermiculite in the noncalcareous soils and Al-smectite in the calcareous soils. sediments.
It was considered that smectite in the calcareous soils and vermiculite in the noncalcareous soils were inherited principally from their parent sediments of the Ganges and the Brahmaputra, respectively, followed by pedogenetic process to form hydroxy-Al polymer in their interlayer.

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A nickel chlorite-like compound was derived from montmorillonite by intercalation of nickel hydroxide layer between the silicate layers. The hydroxide layer was dehydrated in a temperature range of 300° to 400°C, and remained as the oxide between the silicate layers. The structural OH groups of montmorillonite are converted into the oxide ions by the reaction with the remained nickel oxide layer in a temperature range of 400° to 500°C. This conversion leads to a pronounced thermal stabilization of the silicate layers up to 800°C, though the untreated montmorillonitesuffers a destructive dehydration starting at temperatures about 650°C.

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Brown Hill Soil and five terrace soil types (Shallow Red Brown Terrace Soil, Deep Red Brown Terrace Soil, Brown Mottled Terrace Soil, Shallow Grey Terrace Soil and Deep Grey Terrace Soil) were investigated to characterize their clay mineralogical compositions as a part of the systematic studies of General Soil Types of Bangladesh.
The clay of Brown Hill Soil was rich in mica and hydroxy-Al interlayered vermiculite with relatively low contents of smectite, vermiculite, kaolinite and chlorite (less than 10%). In contrast to hill soil, all five terrace soil clays examined were differentiated by the trace or very low presence of smectite and vermiculite, which were also different from the clays of previously studied calcareous and noncalcareous soils. The main characteristics of terrace soils were the presence of kaolinite/smectite along with the higher presence of mica and kaolinite. The interstratification of other types were very complex and could not be easily identified by means of XRD only. Mica seems to be weathered to kaolinite/smectite to kaolinite through some intermediates of hydroxy-Al interlayering and other irregular interstratifications.

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