Recent advancements of mineralogy on planetary materials have been reviewed to propose several topics for future studies. Comparisons of formation and evolution of planetary materials in planets of different sizes and histories enabled us to formulate a new veiw on evolution of planetary materials in the solar system. Circum steller grains in carbonaceous meteorites provided us with a new window to the stars. Hydrothermal alteration of carbonaceous chondrites left us a question what is the true primitive materials of the solar system. A large parent body of chondrites may facilitate minor differentiation even for the chondritic source materials. Impact metamorphism might have been an important process of the protocrust of protoplanets. New meteorites from the mare region of the moon suggested more diversity of materials will be obtained in future form the moon etc. What are representative Earth's minerels as a planetary materials? To answer these questions and to form more general views on planetary materials evolution, it will be required a more deep insight into planetary materials with the aid of newly developed equipments.

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The present status of the cosmology is briefly reviewed, specially paying attentions to new observational facts. In the first, the hierarchical structures of the nature is overlooked in relation to the fundamental forces between matters. This viewpoint is applied to the evolution of the universe based upon the big bang model as a history of bifurcations and materalizations of the forces. At the same time, the large-scale structures in the universe which are discovered in this decade are presented, and the structure formation scenario is shortly explained. It is shown that the, so called, dark matter problem is serious for understanding the formation of large-scale structures. Including these problems, the future expectations to observational cosmology are finally added.

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When one crystalline material changes to another with the loss or gain of part of the material, and there is accord in three dimensions between the initial and final lattices, then the transformation can be characterized as topotactic. In the topotactic transformation from γ-FeOOH to γ-Fe₂O₃, controlling features appear to be the close-packed oxygen frameworks in the interstices of which the mobile iron ions can migrate. The reaction between BaO·6Fe₂O₃ particles with the hexagonal shape and Fe(OH)₂ fine particles in the aqueous solution generates Fe₃O₄ particles with the same shape as that of BaO·6Fe₂O₃. BaO·6Fe₂O₃ changes to Fe₃O₄ with the loss of Ba and O atoms in BaO·6Fe₂O₃, which comes from the reaction with protons generated by oxidation of Fe(OH)₂ to Fe₃O₄.

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The properties of materials are considerably changed by high pressures. Therefore, it is possible to obtain the different properties and materials from the usual ones if we apply the high pressure to sysnthesis of materials. Because metals are extracted from minerals, even intermetallic compounds in alloys have simpler properties and structures than the minerals. Conversely, this simplicity can help us understand the phenomena in alloys under high pressures. This article reviews the diffusion, solid reactions, phase transformations and phase equilibrium in alloys under high pressures.

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Growth mechanism of oxide crystals from a heterogeneous condition of solid-melt mixtures formed by incongruent melting has been analyzed using a newly developed in-situ observation system, which is composed of a time-resolving X-ray powder diffraction apparatus using a PSPC (Position Sensitive Proportional Counter) combined with an optical microscope, images of which are detected by a CCD sensor and stored into a video-recording system. Measurements are carried out on the oxide superconductor system Y-Ba-Cu-O, where well-habited single crystals of the superconductive compound YBa₂Cu₃O_x are easily obtained from a mixture of solid Y₂BaCuO₅ and liquid with the aid of the peritectic reaction. The results indicate that recrystallization by Ostwald ripening plays a main role in such a heterogeneous condition and diffusion of YBa₂Cu₃O_x molecules in the liquid phase determines the whole growth rate.

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The method to estimate the cooling rate of meteorites on the basis of atomic diffusion in minerals is summarized. The best-fit cooling rate and burial depth are obtained by fitting a profile calculated by solving the diffusion equation to the observed chemical gradient and the width of lamellae measured by electron microprobe. The thickness of a eucntic crust of the HED parent body was estimated to be about 10 km from augite exsolution in pyroxene. A rapid cooling of a few hundreds °C/yr for pallasite was obtained on the basis of chemical zoning in olivine. Some problems with estimation of the cooling rate are also reviewed.

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Isothermal experiments under hydrothermal conditions were carried out at four different temperatures as a function of time and H₂O content (0.3-2.2wt%) for the purpose of examining the effect of H₂O on kinetics of the Mg₂GeO₄ olivinespinel transformation. The results reveal that H₂O can activate the transformation with increase of its content at least up to∼2wt%. The transformation process in the presence of H₂O was discussed and a new model via an intermediate state was proposed, that is, atoms constituting the olivine may once dissolve into the supercritical fluid and then precipitate into the spinel structure.

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We cannot thermodynamically determine what silicate minerals are formed at low temperatures (below 300°C) because metastable phases are formed at low temperatures. To determine the phases formed at low temperatures, we need to describe the precipitation and dissolution reactions in terms of kinetics. A metastable phase has entropy higher than its polymorphic stable phase. Using a simple model, we explain that the precipitation rate is proportional to exp(S/k). Thus, a metastable phase precipitates quickly, and its polymorphic stable phase precipitates slowly. The equation including the entropy term and activation-enthalpy terms may well explain the rates of precipitation and dissolution.

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Kinetics and reaction mechanisms in polysomatic reactions of biopyriboles were reviewed in relation to mineralogical usage of HRTEM. HRTEM studies clarified the reaction mechanism and the polymerizing process from pyriboles to talc structure. Many zipper termination channels as reaction front were observed by tracing back from the obtained I-beam structure images. Another tunnel-like structures were found e.g. in the specimens of oxyhornblende, which may correspond to mass transfer tunnel in decomposition processes to form oxyhornblende. Such channels that play an important role in reaction process may be present in varieties of rock forming minerals. HRTEM method may become a kind of powerful tool to disclose such reaction mechanisms and reaction processes.

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Numerical analyses of water-rock interaction (metasomatism) require the precipitation/dissolution kinetics quite different from that of a single mineral in hydrothermal solutions: 1) in replaced zones of bimetasomatism, there may be a kinetics obstructing mineral precipitation in stationarily oversaturated conditions, and 2) at replacement fronts of infiltration metasomatism, precipitation/dissolution rates of reacting minerals may be controlled by the lowest concentration component notwithstanding their reaction surfaces when the concentration of the component is extremely lower than the others.

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