Structural maps evidence the presence of an ultra-minor calcite phase in a carbon sample prepared from C60 at room temperature and high pressure. (a) The two-dimensional reconstruction (87 × 87 voxels) shows the capillary and the sample, composed of capillary, cubic diamond, sp3 amorphous carbon, ferrite and calcite; the grains of calcite occupy only four voxels. (b) The summed pattern derived from all measured positions (y) and orientations (ω), with a focus on the 2θ area where the main calcite diffraction peak should appear. (c) The selective pattern for different phases extracted by using the reverse analysis process, from voxels containing (i) capillary, (ii) calcite ultra-minor impurity, (iii) amorphous sp3 phase, (iv) ferrite impurity and (v) crystallized cubic diamond. This selective pattern extraction allows the cell parameter determination of the CaCO3 impurity (, a = 4.991, c = 17.062 Å) (adapted from Bleuet et al., 2008).