Mineralogy, defect microstructure and shock metamorphismof Hayabusa particle RB-QD04-0042
F. Langenhorst1, D. Harries1, K. Pollok1 and P.A. van Aken2.
1
Institute of Geoscience, Friedrich Schiller University Jena, CarlZeiss-Promenade 10, D-07745 Jena, Germany. E-mail:
Falko.Langenhorst@uni-jena.de. 2Max Planck Institute for Intelligent Systems, Heisenbergstr. 3, D-70569 Stuttgart, Germany.
Introduction: In the first international announcement of opportunity for Hayabusa sample investigation we have received
two precious samples [1]: RA-QD02-0115 and RB-QD04-0042.
Here we report detailed scanning (SEM) and transmission electron microscopic (TEM) investigations of Hayabusa sample RBQD04-0042, which was originally described to be mainly composed of olivine. Our study aimed at characterizing the mineral´sdefect microstructures as clues to the origin of asteroidal regolith.
Methods: Mineral grains and morphology of RB-QD04-0042
were at first studied by scanning electron microscopy and energy
dispersive X-ray microanalysis (EDX) using a FEI Quanta3D
cross beam workstation. Furthermore, this workstation was usedfor precise focused ion beam (FIB) preparation of TEM foils. Defects and mineral structures were subsequently studied by meansof a Philips CM200 transmission electron microscope equippedwith an EDX microanalysis system.
Mineralogy: The olivine grain RB-QD04-0042 being 40 x
50 µm in size turned out to carry an intimate 10 µm wide intergrowth of FeNi alloy and iron sulfide on its surface. Furthermore
a 6 µm diameter diopside inclusion emerged in the course of FIB
cutting of the olivine.
TEM analyses of the FeNi alloy show a high Ni content of
about 50 atom% and electron diffraction patterns reveal a facecentered cubic (fcc) structure, both being compatible with tetrataenite [2]. Electron diffraction patterns of the iron sulfide werein agreement with the stoichiometric iron sulfide troilite.
Defect microstructures: All phases discovered in the SEM
were then studied by TEM in terms of their defect microstructures. Olivine contains locally a high density of [001] dislocations, while in other regions olivine is devoid of defects. Tetrataenite exhibits a large number of mechanical microtwins anddislocations. Troilite contains some stacking faults with partial
dislocations but is mainly characterized by a recrystallization texture with numerous subgrains composing the entire grain. Diopside is basically defect-free.
Discussion: In agreement with previous studies [2] the compositions of silicates and FeNi alloy point to an ordinary chondrite signature of Hayabusa dust. The majority of defects foundin RB-QD04-0042 minerals are known to form by shock metamorphism, in particular the [001] dislocations in olivine and themicrotwins in tetrataenite. The heterogeneous distribution of defects may indicate micro-impacts as possible cause.
Acknowledgments: Financial support was provided by theDeutsche Forschungsgemeinschaft (LA 830/14-1). We are very
grateful to JAXA for providing access to Hayabusa samples.
References:[1] Abe M. et al. 2012. Meteoritics & Planetary Science
47:A35. [2] Uehara et al. 2011. EPSL 306: 241-252. [3] Nakamura T. et al. 2011. Science 333: 1113-1116.