This paper reviews on crystal chemistry of plagioclases and geochemical roles of their megacrysts including native coppers and hydrocarbons, discussed in two parts.Part I. Structural classification of feldspar compositions can be allocated into four types; feldspar, paracelsian, hexacelsian and hollandite structures. Though the phase relation between the first and the second types has been open to question, recent probing of their isotropic temperature factors and bond-valence theory to the M-sites intensifies that feldspars are in the wide stability field from low to high temperatures under low pressures, and that high pressure and low pressure are the preference field for paracelsians. Though very common in north-east part of Japanese island and Izu-Bonin arcs, anorthite megacrysts have never been found in other districts in Japan and have been rare in world-wide occurrences. Native coppers, verified by chemical shift method of EPMA and X-ray microdiffraction, are found to be included by anorthite megacrysts from Japanese island arc and by labradorite ones from the continental margin of North America. These anorthites in the basaltic lavas are of approximately 1 to 3 cm size and often contain several corroded Mg-olivines scattering as single crytals less than a few mm long. The plagioclase megacrysts show no chemical zoning, but the anorthites with the Al/Si ordered state have partings developed in places whereas the labradorites are of the AUSi disordered structure indicative of high temperature type. Each role in their plagioclase structure establishes Mg, Fe, Al and Si cations as a few minor endmembers of CaFeSi₃O₈, CaMgSi₃O₈, AlAl₃SiO₈ and_??_Si₄O₈ for the solid solutions. Furthermore micro-inclusions of native zinc, copper and brass scattering in the red-clouded anorthite megacryst frozen by the supercooling environment could have an implication for a precusor to Kuroko deposits. Review (1) discusses both structural tolerance of plagioclases and their megacrysts including native coppers.

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In order to elucidate many geophysical problems induced from the global techtonics, dynamics of the mass transfer has attracted an interest. In association with the seismic researchs, material transformations, such as transition, decomposition, recrystallization, melting, etc. have been also greatly intrested under the conditions of heating, compression and stress field. Pressure-induced amorphizations of many minerals such as quartz, cristobalite, tridymite, anorthite, serpentine, fayalite and several other hydrates have been reported. These amorphizations and shear-instability will play a role to conduct the transformational ductile flow in the subduction zone, which would be the origin of the deep earthquake. Several different types of the pressure-induced amorphization were proved by the X-ray diffraction studies under high pressure and heating condition using multianvil high-pressure appararus and diamond anvil pressure cell. If the amorphization is the quenchable case, the pressure-quenched amorphous substance was examined by electron microscope, Raman spectrosope, EXAFS together with X-ray diffraction study.

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The anomalous X-ray scattering(AXS) has received much attention for the structural characterization of various inorganic substances. This review provides the fundamentals of AXS technique and its potential power for determining the environmental structure around a specific element as a function of radial distance. The usefulness of this method was demonstrated with the selected examples of GeO₂-Bi₂O₃ glasses and a YBa₂Cu₃O₇-x superconductor. The quantitative analysis for the multiphase system by the AXS measurements has also been discussed using the result of Cu₂S/CaFe₂O₄ mixtures.

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The materials formed on the surface of the Earth are completeley different from those formed in the Earth's interior. Surface materials are usually metastable and non-crystalline, while the interior materials are stable and crysatlline. Because the surface materials are reactive with inorganic ions and organic molecules, they play an important role in the Earth's environment. However, little is known for these materials; the arrangement of atoms is not known in detail, and no theory predicts their stability and reactions. New approaches, research tools and theories are necessary for understanding the surface materials. Integration of those studies may open a research field original in geoscience. We expect that the researches on the surface materials attract attention of major mineralogist in Japan.

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