Vibrations involving hydroxyls in the infrared spectra of two synthetic 7 Å trioctahedral minerals (amesite and aluminian lizardite) and of seven natural 14 Å minerals (five trioctahedral chlorites of the Mg–Fe series, sudoite, and cookeite) have been investigated by comparison of the spectra with those of partially deuterated forms obtained by hydrothermal treatments with D₂O. The results are interpreted to indicate that the OH bands between 850 cm⁻¹ and 600 cm⁻¹ in the trioctahedral minerals arise from librations of the outer OH in the 7 Å minerals or the interlayer OH in the 14 Å minerals, expressed by (SiAl)O–OH (∼800 cm⁻¹) and (SiSi)O–OH (∼720 cm⁻¹), and of the inner OH in the 7 Å minerals or the 2 : 1 layer OH in the 14 Å minerals (∼650 cm⁻¹). These librations are correlated with the OH stretching vibrations in a reversed frequency relation. The shoulders around 930 cm⁻¹ in sudoite and cookeite are confirmed to be due to the dioctahedral 2 : 1 OH. Some additional information on the OH stretching bands and on the lattice vibration bands has also been obtained.

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The WMIN program of Busing (1970) in which the Born-type repulsive energy is assumed to calculate the ‘lattice energy’ of crystal, has been applied to estimate the repulsive parameters of four transition metals. The repulsive parameters, ionic radius A_i and ionic compressibility (softness parameter) B_i for Mn²⁺, Fe²⁺, Co²⁺ and Ni²⁺ are obtained from the structural data of Mn₂SiO₄, Fe₂SiO₄ Co₂SiO₄ and Ni₂SiO₄ (olivine structure) by the nonlinear least-squares refinements. The A_i and B_i parameters for Mg²⁺, Si⁴⁺ and O²⁻ ions determined previously for α-Mg₂SiO₄ (forsterite) were employed and fixed during the refinements. The ionic radii thus obtained have been compared with those of traditional ionic radius (Shannon and Prewitt, 1969) to explain their applications to the crystalchemical study of these minerals.

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The structures of anorthite and albite melts have been investigated with the X-ray diffraction method. The scattered intensities were measured at 1600°C and 1200°C on the anorthite and albite melts, respectively. The radial distribution function reveals that the basic structural units of the two melts are the TO₄ (T=Si, Al) tetrahedra. From least-squares fitting of the observed S·i(S) values to those of model structures, it was found that the framework of the tetrahedra in the anorthite melt has close similarity to that in the anorthite structure at high temperature within the short of r≤5Å, based mainly on the four-membered rings, and the framework in the albite melt to the low-tridymite structure where the six-membered rings predominate.

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