Nanometre CaO and pure carbon smoke particles were collected at 38-km altitude in the upper stratosphere in\ud the Arctic during June 2008 using DUSTER (Dust in the Upper Stratosphere Tracking Experiment and\ud Retrieval). This balloon-borne instrument was designed for non-destructive collection of solid particles\ud between 200 nm to 40 mm. We report here on micrometre CaCO3 (calcite) grains with evidence of thermal\ud erosion and smoke particles that formed after melting and vaporisation and complete dissociation of some of\ud the CaCO3 grains at temperatures of approximately 3500 K. These conditions and processes suggest that the\ud environment of this dust was a dense dust cloud that had formed after disintegration of a carbonaceous\ud meteoroid during deceleration in the atmosphere. The balloon-borne collector must have coincidentally\ud travelled through the dust cloud of a recent bolide event that had penetrated between 38.5 and 37 km altitude.\ud This work identified a previously unknown meteoric smoke forming process in addition to meteoric smoke\ud particles due to photolysis-driven oxidation of mesospheric metals from meteor ablation that had settled into\ud the upper stratosphere

Abstract-We present the analyses results of two bulk Terminal Particles, C2112,7,171,0,0 and C2112,9,171,0,0, derived from the Jupiter-family comet 81P/Wild 2 returned by the Stardust mission. Each particle embedded in a slab of silica aerogel was pressed in a diamond cell. This preparation, as expected, made it difficult to identify the minerals and organic materials present in these particles. This problem was overcome using a combination of three different analytical techniques, viz. FE-SEM/EDS, IR, and Raman microspectroscopy that allowed identifying the minerals and small amounts of amorphous carbon present in both particles. TP2 and TP3 were dominated by Ca-free and low-Ca, Mg-rich, Mg,Fe-olivine. The presence of melilite in both particles is supported by IR microspectroscopy, but is not confirmed by Raman microspectroscopy, possibly because the amounts are too small to be detected. TP2 and TP3 show similar silicate mineral compositions, but Ni-free and low-Ni, subsulfur (Fe,Ni)S grains are present in TP2 only. TP2 contains indigenous amorphous carbon hot spots; no indigenous carbon was identified in TP3. These nonchondritic particles probably originated in a differentiated body. This work found an unanticipated carbon contamination following the FE-SEM/EDS analyses. It is suggested that organic materials in the embedding silica aerogel are irradiated during FE-SEM/EDS analyses creating a carbon gas that develops a strong fluorescence continuum. The combination of the selected analytical techniques can be used to characterize bulk Wild 2 particles without the need of extraction and removal of the encapsulating aerogel. This approach offers a relatively fast sample preparation procedure, but compressing the samples can cause spurious artifacts, viz. silica contamination. Because of the combination of techniques, we account for these artifacts.

ABSTRACT. Iron-rich (Fs:En ~0.8) calcic pyroxenes that have been subjected to granulite-facies metamorphism contain up to seven generations of exsolution lamellae. They can be grouped into four stages. In stage 1 pigeonite exsolved parallel to '00l ' and '100' (where "hkl' signifies ~ (hkl)) and mostly inverted later to orthopyroxene. During stage 2 orthopyroxene exsolved parallel to (100), while during stage 3 orthopyroxene was quickly followed by metastable '001' pigeonite. The stage 3 precipitates clearly grew and thickened together for some time. During stage 4 a '100' pigeonite was exsolved. The stage 3 and 4 precipitates show evidence of reheating, dissolution and later, renewed growth. Sometimes orthopyroxenes of stage 3 have crossed a '001' pigeonite lamella and caused it to invert by a shear mechanism.Chemical analysis shows no rotation of the tie lines between Ca-rich and Ca-poor phases, in contrast to previous studies of Skaergaard and Bushveld pyroxenes. The geothermometers of Wood and Banno (1973) and Wells (1977) indicate solidus temperatures of about 850 ~ and 900 ~ respectively, but the geothermometers were found to be unsuitable for subsolidus conditions. We estimate the pressure to have been about 9 kbar during solidification. Estimates of nucleation temperatures obtained from the orientations of the exsolved lamellae (Robinson et al., 1977) were 850 700 ~ for stage 1, and 600 400 ~ for stage 3. We believe this geothermometer to be unreliable for the low temperatures involved in stage 4. THE mechanism of precipitation (exsolution) and the nature of the subsolidus phases in lunar and terrestrial pyroxenes have been the subject of many studies in the past two decades. Extensive petrographic, single-crystal X-ray diffraction and, more recently, transmission electron microscopic (TEM) studies have shown that subsolidus phase relations in pyroxenes from slowly cooled igneous and metamorphic rocks may be complex (e.g. Ross et al., 1972;Jaffe et al., 1975;Robinson et al., 1977; Rietmeijer and Champness, 1980a;and Nakajima and Hafner, 1980). Copyright the Mineralogical SocietyRobinson et al. (1971, 1977) have shown that the habit planes of exsolved Ca-rich and Ca-poor clinopyroxenes are not always parallel to (001) and (100) as had previously been assumed, but are (h01) planes that may deviate several degrees from the exact (001) and (100) orientations. The relative equilibrium cell dimensions of the phases are such that, for coherent exsolution of one phase from another, one principal strain is of opposite sign to the other two (the strain quadric is a hyperboloid). There are thus two directions perpendicular to the intermediate principal axis of strain (the y-axis) for which the strain is zero. Because the strain parallel to y, the elastic anisotropy and the chemical-energy component of the interracial energy are small, the orientations of the exsolution lamellae are essentially those of the 'planes of best fit' at nucleation. Robinson et al. (1971Robinson et al. ( , 1977 showed that slowly cooled...

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