Electrostatic energies of nine mantle minerals in the MgO–SiO₂ system (forsterite, modified spinel, spinel, orthoenstatite, clinoenstatite, ilmenite, perovskite, periclase and stishovite) were calculated by the method of Bertaut (1952) with error estimations.
It is noted that the structure of ortho- and clinoenstatites have atomic geometries which are skillfully arranged to gain low electrostatic energies compared with ilmenite and perovskite, although the former minerals have lower densities than the latter. This low energy results from the low values of Mg1, O3A and O3B ions in these pyroxenes but mainly from the fact that O2A and O2B oxygens, which are “undersaturated” with Pauling’s bond-strength sums, do not have so high values as O1 of modified spinel which are also “undersaturated” with them.
Periclase and hence, Mg and O of the mineral exhibit an extremely high same value, showing a clear contrast with other minerals even in the high pressure. This indicates that Fe²⁺ ion prefers magnesiowüstite (which is isostructural with periclase) in the cation distributions of Fe²⁺ and Mg²⁺ between perovskite and magnesiowüstite, and spinel and magnesiowüstite which might coexist in the mantle transition zone. This is qualitatively consistent with the high pressure experiments studied by high pressure workers.

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Beidellite was synthesized from sodium aluminosilicate glass at a hydrothermal pressure of 100 MPa and at temperatures of 250, 300, 350, 400 and 450°C. The initial water/solid ratio of the starting materials was varied in the range 0.155 to 2.17. The run products were analyzed by the powder X-ray diffraction (XRD) method. Correlations among the water/solid ratio, temperature of synthesis, yield of beidellite and its crystallinity indicated: (1) Amount of water intercalated in the structure was limited to three layers even in water-excess condition of synthesis at high pressure and temperature. (2) Beidellite, crystallized from glass by hydration, was in the form of a two-dimensional flake. The dimensions and thickness of a flake were independent of the temperature of synthesis and the water/solid ratio, and were not increased by further hydration.

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Degassing process of argon from young geological materials by low temperature stepwise heating was examined to improve the precision on K–Ar dating of the materials. The radiogenic argon was released out from the groundmass, biotite, hornblende and plagioclase phenocrysts of volcanic rocks at temperatures higher than 500°C, and from sericite at temperatures higher than 400°C. Therefore, pre-heating before argon analysis is necessary; at 400°C for 1 hour for volcanic materials and at 300°C for sericites to remove the adsorbed atmospheric argon on them. HCl treatment for sericites having impure materials improves the precision, and HF treatment of volcanics which have a glassy surface produced as a result of the crushing process would improve the precision.

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