Simulated diagenesis of the iron-silica precipitates in banded iron formations: Data Repository

This XRD dataset derives from experiments we performed bubbling 49 ppm O2 into simulated Archean seawater and then aging the produced precipitates at 25 degrees C, 80C, 150C, and 220C. Precipitate slurries were extracted from experimental samples and pipetted as 20 µL subsamples into Cole-Parmer Kapton tubes to keep anoxic during XRD analysis. Samples were sent to McMaster Analytical X-Ray Diffraction Facility (MAX) for XRD analysis using a Bruker D8 DISCOVER cobalt source tube (Co-XRD) with a DAVINCI.DESIGN diffractometer. More details on methods in associated article. Resultant XRD measurements of our samples yielded patterns showing increasing crystallinity with temperature. The bubbled experiment aged for 40 days at 25 °C produced a large and diffuse diffraction peak corresponding to the Kapton tube but no other sharp diffraction peaks, suggesting an amorphous to minimally crystalline product. A broad peak in the 25 °C precipitate, that persisted through the higher-temperature aging treatments, may correspond to ferrihydrite. The bubbled experiment aged at 80C contained diffraction peaks consistent with a serpentine group silicate and a spinel group oxide (like magnetite). After the 150 °C treatment, samples showed sharper peaks consistent with a serpentine group silicate and spinel group oxide. After 220 °C aging, the precipitates showed a continued narrowing of the diffraction peaks for a spinel group oxide, reflecting an increase in crystal size and/or crystallinity, but smaller and less sharp serpentine group peaks.