Fig. 7: 40-day dehydration experiment of pure ferrihydrite.
From: Detection of ferrihydrite in Martian red dust records ancient cold and wet conditions on Mars
a Spectra of pure ferrihydrite under dehydrating conditions for almost 1000 h and b background-removed 2 L ferrihydrite X-ray diffraction patterns of before (black) and after (red) dehydration. In a exposure to simulated present-day Mars-like conditions results in significant dehydration and water loss in ferrihydrite, as indicated by the removal of the 1.9-µm band. However, the pure ferrihydrite sample did not change phase nor crystallize as suggested by the XRD analysis in b. The small spectral shift in a from 1.41 to 1.40 µm occurs as adsorbed water (which absorbs light at slightly longer wavelengths) is removed from the system, leaving only structural OH/H2O groups contributing to the absorption band123,124. Source data are provided as a Source Data file.
