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Project Progress

During the 2005-2006 year, I conducted a comparison of the textures, mineralogy and bulk compositions of the fine-grained rims of carbonaceous chondrites and aggregate interplanetary dust particles (IDPs). These IDPs are commonly thought to originate from cometary tails. Aggregate IDPs and meteoritic fine-grained materials share similar textures, mineralogies and bulk compositions. In order to continue to explore the possible connection between comets and carbonaceous chondrites, I have been performing a series of experiments to alter amorphous smokes, similar in composition to the materials found in IDPs and chondrites. Last year, I exposed amorphous silicate smokes, made by Dr. Joe Nuth, to water at room temperature, 5°C and ice at -20°C and -80°C to simulate conditions on meteoritic parent asteroids and the outer solar system. I have analyzed 16 time steps spanning over 6 months and derived the kinetics properties of the reactions (crystal growth with time). Initially, the Mg-silicate smokes hydrate into an amorphous gel and then within three days, phyllosilicates grow (Fig. 1). The Fe-silicate smokes show no signs of hydration after 6 months of contact with distilled water (Fig. 2). I presented this work in an oral presentation at the annual Meteoritical Society (MetSoc) Meeting, last August. After exposure to H₂O, the smokes were characterized using the transmission electron microscopes (TEM) here at the Biological Electron Microscopy Facility (BEMF). At UH, I have used a combination of TEM techniques including bright and dark field imaging to identify changes in textures, diffraction patterns to discern the resultant mineralogy and element mapping to recognize any elemental redistribution.

This year, I set up a series of experiments with different mixtures of Mg- and Fe-smokes to test the hypothesis that the lack of reaction of the Fe-smokes with water is due to a thermodynamic barrier which may be overcome in the presence of the exothermic Mg-smoke hydration. I mixed the smokes in Mg:Fe ratio of 2:1, 1:1 and 1:2. The smokes mixtures do hydrate, although more slowly than the Mg-smoke alone. The rate of reaction of the Mg-Fe smokes mixtures is proportional to the Mg:Fe ratio; the higher the Mg:Fe ratio, the faster the reaction. Also, the formation of phyllosilicates is retarded with the first crystallites appearing in the highest Mg:Fe ratio mixture after 1 month. The first stage of alteration is that the rounded particles forms necks between each other, then morph into a silicate gel with high density concentrations corresponding to the original particles. The next phase of alteration is that the amorphous gel loses the areas of high density, followed by the appearance of phyllosilicate crystallites. I presented these results in an oral presentation at the 2007 Lunar and Planetary Science Conference (LPSC) in March.

The results of the ice experiments show the hydration of the Mg-silicate smokes, similar, but at a slower rate, to the hydration exhibited at room temperature and at ~5°C. The rounded particles of some of the smokes neck into an amorphous silicate gel in a similar manner as that observed by the Mg-Fe smokes mixtures. No phyllosilicates were observed. The Fe-silicate smokes do not react even after exposure to ice for 12 months.

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