THE IRRADIATION-INDUCED OLIVINE TO AMORPHOUS PYROXENE TRANSFORMATION PRESERVED IN AN INTERPLANETARY DUST PARTICLE

Amorphization of crystalline olivine to glass with a pyroxene composition is well known from high-energy irradiation experiments. This report is on the first natural occurrence of this process preserved in a chondritic aggregate interplanetary dust particle. The Fe-rich olivine grain textures and compositions and the glass grain compositions delineate this transformation that yielded glass with Fe-rich pyroxene compositions. The average glass composition, (Mg, Fe)3Si2O7, is a serpentine-dehydroxylate with O/Si = 3.56 ± 0.25, (Mg+Fe)/Si = 1.53 ± 0.24, and Mg/(Mg+Fe) = 0.74 ± 0.1. These measured atomic ratios match the ratios that have been proposed for amorphous interstellar silicate grains very well, albeit the measured Mg/(Mg+Fe) ratio is lower than was proposed for amorphous interstellar silicate grains, Mg/(Mg+Fe) > 0.9.