Abstract
This paper presents a unique correlative microscopic method for the structural characterization of extraterrestrial minerals. A fragment from the pallasite Seymchan meteorite that consists of olivine grains mixed into a metallic iron matrix with variable nickel content was studied from mm-down to nm-size by using the Raman Imaging and Scanning Electron Microscopy (RISE) and analytical scanning transmission electron microscopy (STEM). Hyperspectral fast acquisition for energy dispersive X-ray spectroscopy mapping of a couple of mm2 large area correlated with additional hyperspectral Raman analysis of smaller regions in the same area on one hand, and hyperspectral analytic STEM investigations at atomic resolution on the other hand, provided valuable information about chemical composition, bonding and crystallography. The analysis revealed particles of troilite, schreibersite and forsterite but also regions of mixed iron oxides, carbonates and amorphous carbon as well as plessite regions with nanometre sized taenite needles dispersed in the kamacite matrix.
Highlights
Pallasites are exquisite meteorites made of millimeter- to centimeter-sized olivine grains and FeNi metal alloys
The electron microscope is equipped with a silicon drift detector from Oxford (UK) for energy dispersive X-ray spectroscopy (EDXS) that allows for fast acquisition of spectra and maps (Schmidt et al, 2019)
Previous neutron tomography investigation showed that the metal component of the Seymchan meteorite consist of a dendrite-like complex network of metals veins (Kichanov et al, 2018)
Summary
Pallasites are exquisite meteorites made of millimeter- to centimeter-sized olivine grains and FeNi metal alloys. The primitive (unaltered) chondrites contain complex mixtures of micrometer sized magnesian olivine and low-Ca pyroxene, amorphous ferromagnesian silicates, Fe, Ni-metals, sulphides and organic phases. These meteorites contain fractions of material that was probably vaporized and recondensed during high-temperature transient heating events associated with the formation of chondrules and refractory inclusions (Kereszturi et al, 2015; Bizzaro et al, 2017). The differentiated meteorites, on the other hand, are fragments of asteroids that experienced chemical and physical changes that led to a separation of the metallic part from silicates leading to metallic core and silicate mantle They are considered core-mantle mixtures, and could come from many different asteroid
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