Fig. 3: Fe–Ni alloy and spinel-bearing inclusions in olivine (Ol3) and the valence state of iron in them.
From: Iron disproportionation in peridotite fragments from the mantle transition zone
a Photograph of a peridotite fragment depicting the intergrown of olivine (Ol3) and a K-Grt. b Backscattered electron micrograph showing ubiquitous tiny Fe-Ni alloy inclusions in Ol3, with the dotted square indicating the cutting position of a foil using the focus ion beam (FIB). c High-angle annular dark-field scanning transmission electron micrograph (HAADF-STEM) of the foil in b showing two Fe-Ni alloy inclusions, an elliptic inclusion, and an octahedral inclusion in Ol3. Amorphous silicon dioxide (A-SiO2) is observed next to the octahedral inclusion and an Fe-Ni alloy inclusion. The insets d and e in c are HRTEM micrographs of the octahedral inclusion and the elliptic inclusion. f Representative EELS of Fe L2, L3 core loss edge of a Fe-Ni alloy inclusion, an elliptic inclusion, and Ol3. The peak position of Fe L3 at 710 eV indicates trivalent iron (Fe3+), while at 708.4 eV, it suggests divalent iron and native ion (Fe0/Fe2+)57, respectively.
