The matrix of the CM2 carbonaceous chondrite Murray contains rare micrometer-sized prismatic crystals of aragonite that formed during late-stage parent body aqueous alteration. The aragonite was identified by X-ray microanalysis coupled with electron backscatter diffraction (EBSD), TEM selected area electron diffraction and cathodoluminescence spectroscopy. The sixteen crystals found all occur within loose and elongate submillimeter-sized clusters and one cluster is present in each of the two thin sections studied. Orientation determinations using EBSD show that the c axes of aragonite crystals within each cluster lie roughly in a plane, itself aligned approximately parallel to the long axis of the host cluster. Aragonite is inferred to have crystallized after calcite but before completion of static/impact-related compaction. The clusters developed by growth of aragonite within films of aqueous fluids that had a relatively high Mg/Ca ratio. These fluids were focused within zones of high porosity and permeability along a weak compactional fabric in the matrix and this fabric is also likely to have influenced the orientations of aragonite crystals as they grew. These results suggest that aragonite probably occurs in most of those carbonaceous chondrites that have undergone moderate degrees of parent body aqueous alteration and may provide further insights into the evolution of pore fluid compositions and volumes and the chronology of asteroidal evolution.

NWA 2526 is a coarse-grained, achondritic rock dominated by equigranular grains of polysynthetically twinned enstatite (~85 vol%) with frequent 120 triple junctions and ~10-15 vol% of kamacite + terrestrial weathering products. All other phases including troilite, daubreelite, schreibersite, and silica-normative melt areas make up <~1 vol% of the rock. Oxygen isotopic analyses are well within the range of those for enstatite chondrites and aubrites. We show that the "enstatite achondrite" (Russell et al. 2005) Northwest Africa (NWA) 2526 is actually a partial melt residue of an enstatite chondrite-like lithology that experienced ~20 vol% partial melting. We suggest that the heat source was internal to the parent body. The FeS-Fe,Ni and plagioclase-enstatite partial melts were removed from the parent lithology, leaving NWA 2526 as a residue highly depleted in troilite and lacking plagioclase. Sub-solidus slow cooling and annealing is responsible for the coarsegrained, recrystallized texture of the rock. We also suggest that the parent lithology of NWA 2526, prior to partial melting, experienced a shock event which formed the curvilinear trails of blebs of minor troilite and rare metal that are enclosed in enstatite crystals; thus, these represent relicts. After partial melting and annealing, NWA 2526 experienced a second, relatively mild impact event (<~20 GPa) that caused formation of the polysynthetic twinning in the enstatite. We suggest that the meteorite Zakłodzie, which has been referred to as a "primitive enstatite achondrite" (Przylibski et al. 2005), did not form from a magma of internal origin, but that it is an impact-melt breccia of enstatite chondrite-like parentage, as previously discussed by Burbine et al. (2000) and Keil (2007). Finally, the "metal-rich enstatite meteorite with achondritic texture" Itqiy (Patzer et al. 2001) formed by processes very similar to those responsible for formation of NWA 2526 and is also the residue of ~20 vol% partial melting of an enstatite chondrite-like parent lithology, with the FeS-Fe,Ni and plagioclase-enstatite partial melts having been removed from the residue. It also experienced an impact event after partial melting that was responsible for the formation of the mixed Mg-Mn-Fesulfides and the shock stage S3 features of the enstatite. These similarities indicate that NWA 2526 and Itqiy may have formed on the same parent body. This body was different from the EH, EL, Shallowater and aubrite parent bodies, and NWA 2526 and Itqiy may represent samples from yet another, fifth enstatite meteorite parent body.

Until recently, the SNC meteorites represented the only source of information about the chemistry and petrology of the Martian surface and mantle. The Mars Exploration Rovers have now analyzed rocks on the Martian surface, giving additional insight into the petrology and geochemistry of the planet. The Adirondack basalts, analyzed by the MER Spirit in Gusev crater, are olivine-phyric basaltic rocks which have been suggested to represent liquids, and might therefore provide new insights into the chemistry of the Martian mantle. Experiments have been conducted on a synthetic Humphrey composition at upper mantle and crustal conditions to investigate whether this composition might represent a primary mantle-derived melt. The Humphrey composition is multiply saturated at 12.5 kbar and 1375 degrees C with olivine and pigeonite; a primary anhydrous melt derived from a "chondritic" mantle would be expected to be saturated in orthopyroxene, not pigeonite. In addition, the olivine and pigeonite present at the multiple saturation are too ferroan to have been from a Martian mantle as is understood now. Therefore, it seems likely that the Humphrey composition does not represent a primary anhydrous melt from the Martian mantle, but was affected by mineral/melt fractionations at lower (crustal) pressures.

We present laboratory mid-infrared absorption spectra (2.5 micrometers to 16.0 m) of powdered calcium-aluminum-rich inclusions (CAIs) and matrix separated from the carbonaceous chondrites Allende (CV3.2), Vigarano (CV3.3), and Ornans (CO3.3). Two groups of spectra with different features were found for the CAI: in the first group spectra are dominated by spinel, pyroxene, and sodalite nepheline, where main features occur at 9.3 micrometers, 10.3 micrometers, and 11.3 micrometers. In the second group, characteristic minerals are spinel and melilite with typical band maxima at 11.0 micrometers and 12.3 micrometers, and a broad feature between 14.0 micrometers and 15.0 micrometers. The position of the broad spinel feature probably depends on its iron content. Comparison of band positions in spectra from the CAI components to observed circumstellar emission spectra indicates the potential occurrence of CAI-like material. Pyroxene- and spinel-rich features could occur in spectra of dust around the Herbig Ae star HD104237, the T Tauri star Hen3-600 and the post-AGB star R Sge. Melilite- and spinel-rich components possibly appear in the spectrum of HD104237, Hen3-600, 04187_1927, R Sge, and the planetary nebula Hb 12. There is also indication for a spinel component in dust from the Herbig Ae/Be star HD179218. The spectra of the AGB stars R Cas and Aps show no features of CAI-type spinel.

Recently, samples of allochthonous melt rocks from the v10 km and less than or equal to 1.9 Ga Paasselkä impact structure, SE Finland, were obtained. In this study, we present a first detailed petrographic and geochemical description of clast-rich Paasselkä impact melt rocks. Shock metamorphic features comprise shocked feldspar grains, intensely shocked and toasted quartz, marginally molten and recrystallized clasts thought to have been diaplectic quartz glass, largely fresh and recrystallized feldspar glasses, decomposed biotite flakes, recrystallized fluidal silica glass (originally probably lechatelierite) in partially molten sandstone clasts, all set into a glassy to cryptocrystalline melt matrix. The degree of shock metamorphism of clasts suggests initial whole-rock melting at peak shock pressures of greater than or equal to 35 GPa and post-shock temperatures of up to ~1500 degrees C. Glass components vary in geochemical composition corresponding to the mixed character of the crystalline target rock (i.e., representing different monomineralic and mixed-mineral melts). Feldspar glasses and the fresh glassy to cryptocrystalline melt matrix indicate that the Paasselkä melt rocks are not intensely altered. The geochemical composition of the Paasselkä impact melt rocks is roughly consistent with the compositions of melt rocks from a number of impact structures located within the crystalline basement of the Baltic Shield.

A new olivine-pigeonite ureilite containing abundant diamonds and graphite was found in the United Arab Emirates. This is the first report of a meteorite in this country. The sample is heavily altered, of medium shock level, and has a total weight of 155 g. Bulk rock, olivine (Fo79.881.8) and pyroxene (En73.9-75.2, Fs15.5-16.9, Wo8.8-9.5) compositions are typical of ureilites. Olivine rims are reduced with Fo increasing up to Fo96.1-96.8. Metal in these rims is completely altered to Fehydroxide during terrestrial weathering. We studied diamond and graphite using micro-Raman and in situ synchrotron X-ray diffraction. The main diamond Raman band (LO=TO mode at ~1332 cm^(-1)) is broadened when compared to well-ordered diamond single crystals. Full widths at half maximum (FWHM) values scatter around 7 cm^(-1). These values resemble FWHM values obtained from chemical vapor deposition (CVD) diamond. In situ XRD measurements show that diamonds have large grain sizes, up to 5 micrometers. Some of the graphite measured is compressed graphite. We explore the possibilities of CVD versus impact shock origin of diamonds and conclude that a shock origin is much more plausible. The broadening of the Raman bands might be explained by prolonged shock pressure resulting in a transitional Raman signal between experimentally shock-produced and natural diamonds.