In order to estimate the effect of acidic rain and see water on evolution of early earth environment, artificial chemical weathering of basalt, which is the most widely distributed on the earth, have been experimented chemically and mineralogically under early earth condition. The basalt has been exposed to three kinds of acid solutions at pH 4, carbon dioxide saturated water and distilled water at 50 degree for different periods of time up to 360 days in an open system. The basalt was composed mainly of olivine as a phenocryst, and plagioclase, clinopyroxene and small amounts of volcanic glass in groundmass. The leached sample solutions were collected, and analyzed for dissolved elements using ICP-MS. Morphological and chemical changes of the each mineral surface were studied by SEM, EPMA and microscopy techniques. Alteration products were collected from the surfaces of each mineral and examined using XRD.

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Meteorite searches were performed in the Nansen Icefield near the Sør Rondane Mountains, Antarctica by the joint Belgian-Japanese meteorite search team. A total of 218 meteorites, including two achondrites, were successfully recovered and collected by the team. The meteorites will be termed Asuka 10 meteorites.

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Recently, it has been reported that several carbonaceous chondrites commonly contain chondrule/rim clasts (e.g. Tomeoka and Ohnishi, 2010). The clasts experienced different alteration histories from those of their host meteorites, thus they provide us new information about the formation processes of their parent bodies. It is known that the Tagish Lake carbonaceous chondrite consists of two lithologies (Zolensky et al., 2002). While some authors reported that there is no evidence for brecciation in the carbonate-poor lithology (Greshake et al., 2005), other authors reported that chondrule/rim clasts are commonly observed in the carbonate-rich lithology (Nakamura et al., 2003). We studied texture, mineralogy, and chemical compositions of carbonate-poor lithology of Tagish Lake in detail and found several lines of evidence that dynamic brecciation processes occurred in this lithology.

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CAIs in the Ningqiang carbonaceous chondrite are known to have experienced extensive Na metasomatism and contain various amounts of nepheline. Here we present the results of a detailed mineralogical study of chondrules and matrix in the Ningqiang chondrite. We found that most chondrules contain various amounts of nepheline, formed by replacing plagioclase in the mesostasis. Nepheline is also uniformly distributed as small grains in the matrix. These results indicate that nepheline is common in all over the meteorite and suggest that Na metasomatism was probably an extensive process that involved all of the major components in the Ningqiang parent body.

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We mineralogically and petrologically studied relict ferroan olivines and low-Ca pyroxenes from 26 MMs, survived atmospheric entry heating. Since samples from Itokawa and 81P/Wild2 comet are rich in ferroan silicates, the study is important for understanding the formation process. The samples from the Tottuki icefield and the water well at the Amundsen-Scott South Pole Station were used for the present study. The main results are as follows: (1) 12 MMs showing reverse zoning with relict ferroan olivine in the core, (2) 7 MMs ferroan olivine coexist with low-Ca pyroxene (one magnesian MM and 6 ferroan MMs), (3) 4 MMs bearing iron-sulfide, (4) a MM high-Ca pyroxene, and (5) a MM chromite. We linked the folloing MMs with chemical groups: 4 MMs high-Mn type, 3 MMs equilibrated H chondrite, and one MM shock-melted H chondrite. MMs of the high-Mn type are possibly derived from comet.

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We made a mineralogical study of the shock induced melt veins in the Efremovka CV3 chondrite. The melt veins are often observed near chondrule-matrix boundaries. The SR-XRD and TEM experiments show the clear differences between the melt veins and the normal matrix, especially as to the constituent olivines. The unit cell volume data from SR-XRD and the TEM-EDX analyses consistently indicate that the olivine in the melt veins is poorer in Fe contents than that of the normal matrix. The olivine size in the melt veins is significantly larger than that in normal matrix. The dislocation density in the melt vein's olivine are much lower than those in normal matrix in spite of the evidence of the heavy shock impact.

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We scanned olivine grains in a Martian meteorite to clarify the dissociation mechanism of olivine at high-pressure and -temperature condition induced by a dynamic event on the Mars. TEM observations reveal that micro-texture of olivine dissociation evolves from lamellar to equigranular with increasing temperature at same pressure condition, agreeing with the observations of synthetic samples recovered from high-pressure and -temperature experiments.

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Recent studies focus on cathodoluminescence (CL) analysis to identify high-pressure minerals. In this study, natural and synthetic high-pressure minerals have been characterized by CL analysis to clarify their emission mechanisms. CL spectra of synthetic and Martian meteoritic stishovite have a emission band at ∼390 nm. Synthetic coesite exhibits dull emission peaked below 300 nm and blue emission at ∼380 nm. CL spectra of experimentally shocked sanidine at 40 GPa and Alkali feldspar glasses in Martian meteorite consists of emission bands at 330 and 380 nm in UV-blue region. CL spectrum of KAlSi3O8-hollandite shows emissions at 330, 380, 550, 580, 660, 710 and 730 nm. These results indicate that CL signals can be applicable to identify high-pressure silica and feldspar minerals.

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Pyroxene plymorphism has been compared for chondrites, meteorites form possibly from asteroid 4 Vesta, and lunar crusts to gain better understanding of their formation and evolution.

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It is widely accepted that Vesta had magma ocean shortly after its formation. We suggest that Vesta experienced volcanism after solidification of magma ocean on the basis of thermal history and geochemical characteristics of HED meteorites.

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We analyzed 31 different fragments of Almahata Sitta (asteroid 2008TC3) and found 18 ureilites (16 typical coarse-grained ureilites and 2 fine-grained mosaicized ureilites) with 7 enstatite chondrites (4 EL and 3 EH), 3 ordinary chondrites (2 H and 1 L), 1 unique chondrite, and 2 unclassified samples. The small size of the recovered samples with variable meteorite types suggests that 2008TC3 was a rubble-pile body loosely composed of cm-sized fragments. Originally, a large ureilite parent body was destroyed by an impact and different types of ureilite fragments re-accreted. 2008TC3 was then ejected from the surface by the secondary impact. The chondrite fragments were either accreted with ureilite fragments or accumulated on the surface of the re-accreted body.

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In this study, we focused on eucrites with variable grain sizes that were formed by different cooling histories, and analyzed plagioclase by SR XANES to discuss their redox states during crystallization. We analyzed thin sections of four eucrites, ALHA76005, EETA87520, Petersburg and Piplia Kalan. Plagioclase in ALHA76005, Petersburg and Piplia Kalan these eucrites has nearly identical Fe3+/ sigma Fe ratios. However, the Fe3+/ sigma Fe ratio of EETA87520 plagioclase shows large differences from one grain to another. EETA87520 shows a moderately coarse-grained texture and apparently represents an igneous rock that crystallized in a shallow magma chamber. The result of EETA87520 would be retained if it was under pressure in the underground environment.

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To investigate the chemical composition of parent (primitive) melts of the Martian mantle, we performed melting experiments using a model Martian mantle derived by Dreibus and Wänke (1984) (= DW mantle) at 1.0-4.5 GPa. The chemical compositions of partial melts are systematically related to pressure. The partial melts at higher pressures are characterized in relatively high FeO content, low Al2O3 content, and high CaO/Al2O3 ratio. Based on the experiments, we found that the two olivine-free shergottites (QUE94201, EETA-B) and a olivine-phyric shergottite (NWA5990) resemble the primitive compositions of the DW mantle in major chemistry. Using these three shergottites, we estimate that the melting condition(s) of the Martian mantle are between 1GPa, 1350oC and 2.5GPa, 1420oC.

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We investigated a high-pressure polymorph in a lunar meteorite, NWA 4734 by FE-SEM, Raman spectroscopy, XRD and Cathodoluminescence spectroscopy (CL). Coesite, Stishovite, α-PbO₂-type silica (Seifertite) and vitrified silicate-perovskite are identified in and around the shock vein of NWA 4734. Based on high-pressure polymorph assemblage, a shock pressure condition recorded in NWA 4734 would be at least ∼40 GPa.

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In order to understand formation condition and process of nepheline in meteorites, we conducted hydrothermal alteration experiments of melilite and plagioclase that are typical precursors of nepheline in CAIs and chondrules, respectively. Hydrothermal alteration of melilite and plagioclase under very alkaline conditions produced nepheline hydrate and analcime, respevtively. These products are hydrous Na-Al-rich silicates that are transformed to nepheline by dehydration. Alteration products and the degree of alteration reactions appear to be dependent on pH and volume proportion of the fluid and the starting material.

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