Extended Data Fig. 1: TEM analysis of modified spherulitic magnetite.
a. SE image of a spherulitic magnetite embedded in phyllosilicate. The dotted line shows an extraction location for cross sectional TEM analysis. b. BF-TEM image of a FIB section extracted from the grain surface in (a). c. BF-TEM image of the modified surface of magnetite (Mgt). The magnetite surface is covered by an iron-rich layer (I). The damaged region (D) in magnetite includes crystallographic distortion that shows distinct contrast compared to the substrate. Pt-C is the protective platinum coat. d, e. Position- averaged NBD patterns obtained from circled areas in (c), suggestive of magnetite (superscript M), body-centered cubic (bcc) iron (superscript I), and roaldite (superscript R). Black, blue, and red arrows indicate diffraction spots from magnetite, bcc-iron, and roaldite, respectively. f. HAADF-STEM image of the magnetite surface corresponding to the elemental profile in (g). g. Depth profile of major elements detected near the magnetite surface. The iron-rich layer is located between the dotted lines. Increase in carbon content at the top surface of the magnetite is due mainly to the carbon protective coat and residual carbon compounds in the platinum protective coat. Sample ID is A0104-026006.
