We present data from TEM and NanoSIMS investigations of Murchison (CM2) KFC1 presolar graphites. TEM examinations of graphite ultramicrotome sections reveal varying degrees of graphite disorder, leading to distinctions between well-graphitized onions, more turbostratic platy graphites, and the most disordered cauliflower graphites. Aside from their larger size, platy graphites are roughly similar in isotopic composition and in internal grain properties to the well-graphitized onions. Most carbide-containing platy graphites exhibit large s-process element enrichments (~200 solar Mo/Ti ratios), suggesting origins predominantly in AGB carbon stars. The degrees C isotopic distribution of platy graphites is similar to onions, with representatives in both 12C-depleted (5 < 12C/ 13C < 40) and 12C-enriched groups (100 < 12C/13C < 350) and a pronounced gap in the 40 < 12C/13C < 75 region that contains 75% of mainstream SiCs. The large 12C enrichments combined with the extreme s-process element enrichments suggest formation in an environment inhomogeneously enriched in the nucleosynthetic products of thermal pulses in AGB stars. In contrast, numerous scaly cauliflower graphites show 18O enrichments and lack s-process-enriched carbides, suggesting a SN origin, as was the case for many Murchison KE3 SN graphites. The more turbostratic graphites (platy and scaly) are on average larger than onions, likely resulting from formation in a gas with higher degrees C number density. Oxygen content increases progressively with increasing degree of graphite disorder, which can stabilize these grains against further graphitization and may be a reflection of higher O/C ratios in their formation environments.

The CH/CB-like chondrite Isheyevo consists of metal-rich (7090 vol% Fe,Ni-metal) and metal-poor (720 vol% Fe,Ni-metal) lithologies which differ in size and relative abundance of Fe,Nimetal and chondrules, as well as proportions of porphyritic versus non-porphyritic chondrules. Here, we describe the mineralogy and petrography of Ca,Al-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs) in these lithologies. Based on mineralogy, refractory inclusions can be divided into hibonite-rich (39%), grossite-rich (16%), melilite-rich (19%), spinel-rich (14%), pyroxeneanorthite- rich (8%), fine-grained spinel-rich CAIs (1%), and AOAs (4%). There are no systematic differences in the inclusion types or their relative abundances between the lithologies. About 55% of the Isheyevo CAIs are very refractory (hibonite-rich and grossite-rich) objects, 20-240 micrometers in size, which appear to have crystallized from rapidly cooling melts. These inclusions are texturally and mineralogically similar to the majority of CAIs in CH and CB chondrites. They are distinctly different from CAIs in other carbonaceous chondrite groups dominated by the spinel-pyroxene +/- melilite CAIs and AOAs. The remaining 45% of inclusions are less refractory objects (melilite-, spinel- and pyroxene-rich CAIs and AOAs), 40-300 micrometers in size, which are texturally and mineralogically similar to those in other chondrite groups. Both types of CAIs are found as relict objects inside porphyritic chondrules indicating recycling during chondrule formation. We infer that there are at least two populations of CAIs in Isheyevo which appear to have experienced different thermal histories. All of the Isheyevo CAIs apparently formed at an early stage, prior to chondrule formation and prior to a hypothesized planetary impact that produced magnesian cryptocrystalline and skeletal chondrules and metal grains in CB, and possibly CH chondrites. However, some of the CAIs appear to have undergone melting during chondrule formation and possibly during a major impact event. We suggest that Isheyevo, as well as CH and CB chondrites, consist of variable proportions of materials produced by different processes in different settings: 1) by evaporation, condensation, and melting of dust in the protoplanetary disk (porphyritic chondrules and refractory inclusions), 2) by melting, evaporation and condensation in an impact generated plume (magnesian cryptocrystalline and skeletal chondrules and metal grains; some igneous CAIs could have been melted during this event), and 3) by aqueous alteration of pre-existing planetesimals (heavily hydrated lithic clasts). The Isheyevo lithologies formed by size sorting of similar components during accretion in the Isheyevo parent body; they do not represent fragments of CH and CB chondrites.

Rumuruti chondrites (R chondrites) constitute a well-characterized chondrite group different from carbonaceous, ordinary, and enstatite chondrites. Many of these meteorites are breccias containing primitive type 3 fragments as well as fragments of higher petrologic type. Ca,Al-rich inclusions (CAIs) occur within all lithologies. Here, we present the results of our search for and analysis of Al-rich objects in Rumuruti chondrites. We studied 20 R chondrites and found 126 Ca,Al-rich objects (101 CAIs, 19 Al-rich chondrules, and 6 spinel-rich fragments). Based on mineralogical characterization and analysis by SEM and electron microprobe, the inclusions can be grouped into six different types: (1) simple concentric spinel-rich inclusions (42), (2) fassaite-rich spherules, (3) complex spinel-rich CAIs (53), (4) complex diopside-rich inclusions, (5) Al-rich chondrules, and (6) Al-rich (spinel-rich) fragments. The simple concentric and complex spinel-rich CAIs have abundant spinel and, based on the presence or absence of different major phases (fassaite, hibonite, Na,Al-(Cl)-rich alteration products), can be subdivided into several subgroups. Although there are some similarities between CAIs from R chondrites and inclusions from other chondrite groups with respect to their mineral assemblages, abundance, and size, the overall assemblage of CAIs is distinct to the R-chondrite group. Some Ca,Al-rich inclusions appear to be primitive (e.g., low FeO-contents in spinel, low abundances of Na,Al-(Cl)-rich alteration products; abundant perovskite), whereas others were highly altered by nebular and/or parent body processes (e.g., high concentrations of FeO and ZnO in spinel, ilmenite instead of perovskite, abundant Na,Al- (Cl)-rich alteration products). There is complete absence of grossite and melilite, which are common in CAIs from most other groups. CAIs from equilibrated R-chondrite lithologies have abundant secondary Ab-rich plagioclase (oligoclase) and differ from those in unequilibrated type 3 lithologies which have nepheline and sodalite instead.

Shock-metamorphosed rock fragments have been found in the Australasian microtektite layer from the South China Sea. Previous X-ray diffraction (XRD) studies indicate that the most abundant crystalline phases in the rock fragments are coesite, quartz, and a 10 Å phase (mica/clay?). In addition, the presence of numerous other phases was suggested by scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis. In the present research, ten of the rock fragments, which had previously been studied using SEM/EDX, were studied by micro-Raman spectroscopy. The presence of K-feldspar, plagioclase, rutile, ilmenite, titanite, magnetite, calcite, and dolomite were confirmed. In addition, the high-pressure TiO2 polymorph with an alpha-PbO2 structure (i.e., TiO2II) was found in several rock fragments. Two grains previously thought to have been zircon, based on their compositions, were found to have Raman spectra that do not match the Raman spectra of zircon, reidite, or any of the possible decomposition products of zircon or their high-pressure polymorphs. We speculate that the ZrSiO4 phase might be a previously unknown high-pressure polymorph of zircon or one of its decomposition products (i.e., ZrO2 or SiO2). The presence of coesite and TiO2 II, and partial melting and vesiculation suggest that the rock fragments containing the unknown ZrSiO4 phase must have experienced shock pressures between 45 and 60 GPa. We conclude that micro-Raman spectroscopy, in combination with XRD and SEM/EDX, is a powerful tool for the study of small, fine-grained impact ejecta.