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Diamond BZ270 derives from within a 30 km radius of the small Rio São Luiz, near the town of Juina. The sampling site for diamond JUc4 can be more precisely constrained to 261000 m E and 8708000 m N in WGS84 UTM-projected Zone 21S (Agrosi et al. 2017; Figure DR1). METHODS Micro-Computed X-ray Tomography Micro-Computed X-ray Tomography (Cnudde and Boone, 2013) was carried out using a Scyscan 1172 microtomograph, located at the University of Bari (Italy). A 45-kV X-ray source was used with a current of 218 µA. A total of 1200 absorption radiographs were acquired over a 360 ° rotation with an angular step of 0.3 °. Random movement of the vertical axis and multiple-frame averaging were used to minimize the Poisson noise in the projection images. Beam hardening was reduced by the presence of a 0.5 mm Al-filter between the source and the detector. The nominal spatial resolution for the resulting model was 4.75 µm. The raw data were reconstructed into two-dimensional slice images using the software "NRecon, Skyscan, Belgium". Corrections for the beam-hardening effect and ring artifacts were also applied during the reconstruction process. Micro-CT data were analyzed using the software "CT-analyser, Skyscan, Belgium". Cathodoluminescence Cathodoluminescence images were collected on a Centaurus detector attached to a Hitachi S-3500N scanning electron microscope (SEM; School of Earth Sciences, University of Bristol). Samples were carbon coated prior to imaging. Accelerating voltages were varied between 10 and 20 kV to obtain the best quality images.

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