(a) Diffractogram of the mineral separate (from GRM‐produced samples) taken with Cu–K‐α radiation and a secondary monochromator. Greigite (Gr) is identified as the dominant magnetic mineral (magnetite, denoted as Mg, may be present as well in small amounts). The major impurities from the sedimentary environment are quartz (Qz) and chlorite (clinochlore, Ch). Note the significant Lorentzian broadening of the greigite peaks, indicating a small crystalline coherence length. All peaks are shown on the same 2θ‐scale. The diffractogram was collected between 5° and 90° (2θ) with Cu–K‐α radiation on a computerized Philips Bragg‐Brentano diffractometer equipped with a secondary monochromator. The stepwidth was 0.02° with a counting time of 30 s per step. (b) Typical profile fits of greigite diffraction maxima and the quartz (101) peak which was used as an internal standard.