A part of questions of geoscience in the past entrance examination of Tokyo University was cited as introductory talk. It explains deep geologic disposal of high-level or long-lived, heat-generating radioactive waste and also a relic of natural atomic reactor at Oklo, Gabon. The importance of studying natural analogues is emphasized. The Morro do Ferro Th-REE-deposit at Pocos de Caldas, MG, Brazil, is introduced from geologic, hydrogeological and geochemical aspects. The study of Hatrurium Formation, Israel, is recommended for the understanding of longevity of cementitious seal or grout materials. Some of the results from International Stripa Project are explained. This was a cooperative research and development project by several member countries of the Nuclear Energy Agency of the Organization for Economic Cooperation and Development, and was based on the KBS-3 fuel-waste desposal concept of Sweden. Besides several potentially useful materials having been proposed for sealing nuclear waste repository, the fine spherical grains made from the melt in CaO-SiO₂ system are suggested to be developed. An autoradiograph of granite hand specimen was shown, in which the very slight difference of radioactivity between quarts and K-feldspar was clearly detected. This was obtaind using an imaging plate, which was developed by reseacheres at Fuji Film. Imaging plate technique is going to illuminate many fields relating to radioactivity, x-ray methods or electron micrography.

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Phase transformations of olivine have important roles in the dynamics of the descending slab and the upwelling plume in the earth's mantle. Here we describe effects of phase transformations on the dynamic earth, based on the model mantle geotherm consistent with the temperatures from phase transformations, seismic anelasticity and heat flow data. The topics in this study include thermal structure of the slab, superplasticity of the lower mantle slab, deep focus earthquakes, slab penetration into the lower mantle, and interaction of the descending slab and the upwelling plume with the postspinel phase boundary at the 660-km discontinuity.

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Recent studies of structural changes of silicate minerals under high temperature and high pressure were reviewed. Recently it was found that several high pressure phases transform to amorphous phase or metastable phase during decompression. Examples are MnTiO₃ perovskite/LiNbO₃ phase transition and C2/c /P2₁/c transition in MgSiO₃ enstatite. In order to study these unquenchable phases it is essential to use in-situ observation technique. Existing phase diagrams based on quench experiments should be reinvestigated. For better understanding of the earth's mantle, structure and physical properties of mantle minerals must be studies at its stable P-T conditions rather than at ambient condition.

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Shock-induced phase transformation mechanims of silicate minerals are discussed. The main part of this review is devoted to a description of TEM observation of shock-produced veins in naturally shocked ordinary chondrites containing high-pressure minerals (i.e. (Mg, Fe)₂SiO₄ spinel, (Mg, Fe) SiO₃ garnet, (Ca, Na, K) (Al, Si)₄O₈ hollandite and (Mg, Fe) SiO₃ perovskite). Data from laboratory shock experimets are also referenced. The high pressure minerals in the shock veins are interpreted as quenched materials from shock-produced high-pressure and temperature (ca. 23-28 GPa, 2400-2800°C) silicate melts along the shear deformation bands in the meteorites.

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The α-to-α'_H phase transition in belite leads to the formation of the α'_H-phase lamellae within the parent a phase. The lamellae occur in parallel with ‹210›_α and make an angle of 27°with (0001)_α. This orientation is consistent with the completely coherent interphase boundaries between the a and α'_H phases. The transition is a nucleation and growth process, of which start and finish are shown on Time-Temperature-Transformation diagram. As a function of cooling rate, the phase constitution and microtexture at ambient temperatures can be predicted from the diagram. After the transition the remelting reaction occurs within the inverted α'_H-phase grains, the liquid phase nucleates and grows heterogeneously on the lamella boundaries leading to a decrease in impurity concentration in the host α'_H phase. A variety of microtextures results depending on the interfacial tension between the exsolved liquid and belite host as well as on quenching temperature and cooling rate.

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Reversible phase change optical recording material with a new quarternary system of Ag-In-Sb-Te has been studied. The starting material for the Ag-In-Sb-Te system is a combination of AgInTe₂ with the chalcopyrite structure and Sb. In this work, we report the basic properties of the Ag-In-Sb-Te films investigated by means of DSC, XRD, ED, and HR-TEM. We also discuss the phase change process of the Ag-In-Sb-Te system.

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Vertebrate bone, tooth dentin and enamel, are composed of the so-called biological apatite, though these hard tissues originate and grow in a different manner and show their characteristic microscopic and ultramicroscopic textures. Tooth enamel has the largest and most perfect apatite crystals among them, even though the enamel crystals contain many crystal-imperfections. To realize the formation of these biological apatite, cell mediated crystal formation mechanisms are shortly reviewed.

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