Optimum experimental conditions and accuracy were investigated in quantitative X-ray microanalysis of serpentine-kaolin group minerals (caryopilite, antigorite, kaolinite) and some other sheet silicates (Mg-chlorite, margarite, sericite) by analytical transmission electron microscopy operated in the TEM mode.
Elemental analyses have been carried out at 200 kV on a JEOL JEM-2000FX with a Tracor Northern TN2000 EDX. Experimental conditions were dark current of 103μA, beam current of 4 to 14μA, spot size of 4L (partly 6L which is used at small electron beam of 50nm and 20nm in diameter), condenser aperture of 70μm, and X-ray take off angle of 70°.
The TEM mode gives with wider control over the beam current density on analyzed area, which is controlled by gun bias current (beam current) and 2nd condenser lens current (beam diameter).
The beam damage gives higher Si weight fraction in all studied minerals. The optimum beam current density, which means no change of element compositions, is different in mineral species.
The X-ray absorption effect is observed in serpentines with Mn and Fe. The simple absorption correction method is shown by the linear relationship in a plot of intensity ratio (I_{Mn (Fe)} /I_Si) as a function of I_Mn (I_Fe). The least-squares method was used to determine the straight line, (I_{Mn (Fe)} /I_Si)=a+b (I_{Mn (Fe)} ). Each measured intensity ratio, (I_{Mn (Fe)} /I_Si) m, is corrected using observed intensity, (I_{Mn (Fe)} ) m, by (I_{Mn (Fe)} /I_Si) c=(I_{Mn (Fe)} /I_Si) m-b (I_Mn) m The accuracy of the weight fraction using the ratio techniques is within the X-ray counting statistic under the optimum beam current density, which is unacceptable levels of beam damage.

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Several samples of regularly interstratified Ca-rich 25 Å minerals of hydrothermal origin from two roseki deposits were examined by chemical analysis, X-ray diffraction and IR spectroscopy together with a few rectorites.
These sampls are rich in SiO₂, Al₂O₃ and H₂O which are accompanied by considerable amounts of CaO, Na₂O and K₂O. Interlayer cations of mica-like layers are composed of a considerable amount of Ca. Ca populations are clearly greater than a half of all interlayer cations in mica-like layers and such a sample has not been reported so far. Al-for-Si substitution in the tetrahedral sheets of mica-like layers increases in proportion as Ca contents increase. The characteristic absorption bands of 950-900 cm^-1 and 700-670cm^-1 are observed in IR spectra. The bands are due to Al-for-Si substitution in the tetrahedral sheets. Judging from the chemical analysis and IR spectra, the component of mica-like layer rich in Ca is not that of mica but mainly that of brittle mica (margarite). Expansion characteristics of the Ca-rich 25 Å mineral are similar to those of rectorite and expandable layer is close to beidellite. The mineral is somewhat less expandable that rectorite under the conditions of RH70-80%(Na-saturation) and EG treatment (K-saturation).
The Ca-rich 25 Å mineral reported here is similar to rectorite in its expansion chractristics, but the component of mica-like layers of it is differnt from that of rectorite. Mica-like layer of the mineral must be mainly composed of margarite-like layer. The mineral is mainly composed of 1:1 regular interstratification of dioctahedral brittle mica (margatite) and smectite (beidellite). The mineral dose not strictly correspond to rectorite which is defined as 1:1 interstratified mineral of dioctahedral mica and smectite.

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The mineralogical properties and formation process of kaolinite from the Iriki kaolin deposit were studies. The Hinckley indices of the kaolinite samples have the value between 1.06 and 1.75 indicating relatively ordered structure. The IR absorption frequencies related to Si-0 vibration shifted linearly with increasing degree of disorder. The electron microscopic observation suggested that the kaolinite was formed from smectite under hydrothermal conditions. The growth process of the kaolinite can be divided into two stages. The first stage is formation of irregular-shaped particles. The second stage is dissolution of the irregular-shaped particles and growth of hexagonal-shaped particles. This formation process is controlled by the Ostwald ripening mechanism.

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Charge distribution was calculated for a cluster model of clay minerals using a semi-empirical molecular orbital method (Modified Neglect of Differential Overlap, MNDO). The cluster model was constructed with 4 Si, 4 Al, 22 O, and 16 H atoms, so as to represent a part of 2: 1 type silicate. The calculation showed that the negative charge on the surface O atom tends to decrease, rather than to increase, by isomorphous substitution in both terahedral (Al for Si) and octahedral (hypothetical divalent cation for Al) sheets. It showed, also, that the excess electron due to dissociation of H⁺ from an edge SiOH group is distributed mainly and nearly equally on the original O and Si atoms, and some on the Si and Al atoms in the neighborhood.
The above finding is contrary to the view that the excess electron arising from isomorphous substitution or dissociation of H+ from crystal edge is localized on the limited number of surface O atoms adjacent to the sites of substitution or dissociation. We propose that the finding be taken into account in the study of interaction between clay minerals and other substances such as ions and compounds.

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