**3. Materials and Methods**

A piece of the Brahin pallasite was polished and coated with a carbon film for electron microprobe study. SEM imaging (Figure 1) and microprobe analysis for the main elements were conducted by means of a CamScan 4 scanning electron microscope (SEM) (Cambridge, UK) equipped with a LINK AN1000 energy-dispersive analyzer (LINK Analytical, CA, USA). The following standards were used: chlorapatite (Ca-*K*, P-*K*), enstatite (Mg-*K*), hematite (Fe-*K*). The analysis was carried out at 20 kV acceleration voltage, 0.8 nA beam current, 1 μm estimated beam diameter and 60 s live acquisition time per spot. The check-up for minor constituents was performed with a Microspec WDX-2 wavelength-dispersive X-ray spectrometer (Microspec Corporation, CA, USA) attached to the same SEM. The Mn content was determined using Mn-*K*α line (MnCO3 standard) at 20 kV and 15 nA, whereas the contents of Ni, Co, Na, K and Si were found to lie below the detection limit (less than 0.05 wt.%).

For the purposes of the X-ray structural study, the grain of stanfieldite was extracted from the section and crushed into a few fragments, which were examined under a polarizing microscope in the immersion oil. Several optically homogeneous grains were checked using a Rigaku Oxford diffraction Xcalibur single-crystal diffractometer equipped with a fine-focus sealed tube and graphite monochromator (MoKα, 50 kV, 40 mA). It was found that all checked fragments are optically irresolvable intergrowths, each of them being composed of two or more domains misoriented within 5–10◦. The best selected two-domain grain (0.15 × 0.10 × 0.10 mm) was glued onto a plastic loop and subjected to further data collection. A hemisphere of reciprocal space was collected up to 70◦ at room temperature, and the details are provided in Table 1. Subsequent data processing routines (integration, scaling and *SHELX* files setup) were performed by means of a CrysAlisPro software (Rigaku Oxford diffraction) [44]. The crystal structure has been solved using an intrinsic phasing approach and refined by means of a *SHELX*-2018 set of programs [45] incorporated into the Olex2 operation environment [46]. The details of structure refinement are given in Table 1 and in the crystallographic information file (CIF) attached to the Supplementary Materials (S1).


**Table 1.** Crystal data, single-crystal and Rietveld refinement details for stanfieldite from Brahin.

The X-ray powder diffraction pattern (Table 2) was obtained with a Rigaku R-AXIS Rapid II difractometer (Rigaku Corporation, Tokyo, Japan) equipped with a curved (semi-cylindrical) imaging plate. A ~150 μm ball was prepared from the stanfieldite powder mixed with an epoxy resin and was picked onto a glass fiber. The image acquisition conditions were: Co*K*α-radiation, rotating anode with microfocus optics, 40 kV, 15 mA, Debye-Scherrer geometry, *r* = 127.4 mm, exposure 30 min. The imaging plate was calibrated against Si standard. The image-to-profile data conversion was performed with an osc2xrd program [47]. The unit-cell parameters and occupancies of Mg1–Mg5 sites were refined by the Rietveld method (Table 1, Figure 2) using Bruker TOPAS v. 5.0 software (Bruker Inc., Wisconsin). The occupancies at the M5A site were fixed at the values determined by single-crystal refinement. The atomic coordinates were not refined but were fixed according to single-crystal data. The XPRD pattern (Table 2) was indexed on the basis of theoretical values calculated with STOE WinXPOW v. 1.28 software (Stoe & Cie GmbH, Darmstadt, Germany).

The micro-Raman spectrum was recorded from a random powder sample using a Horiba Jobin-Yvon LabRam 800 instrument (HORIBA Jobin Yvon GmbH, Bensheim, Germany), equipped with a 50<sup>×</sup> confocal objective. The instrument was operated with a 514 nm Ar<sup>+</sup> laser at a 1 nm lateral resolution and 2 cm−<sup>1</sup> spectral resolution. The optics were preliminarily calibrated using a Si reflection standard.


**Table 2.** X-ray powder diffraction data (*d* in Å) for stanfieldite from the Brahin meteorite.

<sup>1</sup> Intensities were normalized to Σ*I*[(600) + (–421) + (420) + (204) + (023)] = 100. Reflections having relative intensity less than 2 at *d* < 4.00 Å have been omitted.

**Figure 2.** Rietveld refinement plot of stanfieldite from the Brahin meteorite.
