Fig. 2
![Fig. 2](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2Fs40623-020-01352-6/MediaObjects/40623_2020_1352_Fig2_HTML.jpg)
Microstructure of initial olivine grains (a, b), olivine grains after the experiment (grain A: c, d; grain B: e, f), and an FIB section from grain B (g, h). a, b Typical olivine grains used as the starting materials. These grains had a smooth surface with smaller olivine particles (~1 μm) attached to them. c, d Grain A was partially covered with precipitation features. Conical etch pits were also detected. e, f Grain B was entirely covered with polyhedral etch pits. Irregularly shaped carbonaceous materials (1–10 μm, white particles) were attached to the surface. g, h An FIB section obtained from grain B (red broken area)