Experimental simulation of aqueous alteration in primitive meteorites and characterization by electron microscopy

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Hydrothermal alteration experiments of olivine powder with several Fe/Mg rations were carried out under acidic and neutral conditions, and TEM observations were made on the run products. Well-developed tubular crystals of serpentine (chrysotile) were synthesized from Fo100 under both acidic and neutral conditons, and from Fo92 and Fo80 under acidic condition. Abundance and size of chrysotile apparently depend on the Fe contents of olivine, i.e. with increasing Fe contents, less and smaller chrysotile was formed. Acidity of the solution plays an important role for the formation of chrysotile. Platy and fibrous crystals of phyllosilicate, probably serpentine, were obtained from Fo50 and Fo20 treated under acidic condition, which are most similar to the phyllosilicates in the CI and CM chondrites. Framboidal aggregates of Fe-rich grains (Presumably Fe-hydroxide) were formed from Fa100 and Fo20, but not phyllosilicate was formed Fa100.