Isabella Pignatelli, Enrico Mugnaioli, Régine Mosser-Ruck, Mustapha Abdelmoula, Jérôme Sterpenich
Applied Clay Science 262 (2024) 107627
Voir en ligne : https://doi.org/10.1016/j.clay.2024.107627
Abstract :
This work investigated the formation conditions of cronstedtite, the most Fe-rich serpentine, using a steel
autoclave lined with Teflon at 90 ◦C, over 167 days, allowing for in situ monitoring of pH, T and P, as well as for
gas sampling. From a starting mineralogical mixture composed of quartz and metal iron, cronstedtite crystallized
in association with, magnetite, akaganeite, ferrihydrite and amorphous silica. This mineralogical association was
not observed in previous syntheses and it is likely related to the experimental conditions of this study. These
conditions also affected the composition and structure (polytypic sequence and crystallinity degree) of cronstedtite,
which are accurately characterized for the first time. Experimental data and thermodynamic modelling
indicate that this Fe-serpentine formed under neutral conditions, -62 < logfO2 < 59, and redox potential
ranging from 0.46 to 0.41 Volts. During the experiment, H2 was generated by iron oxidation in presence of
water, explaining the increase of pressure in the autoclave until 6.8 bar at 90 ◦C. The total amount of H2
generated was of 0.23 mol. The results of this study are useful to improve the understanding of cronstedtite
formation in natural and anthropic environments. They also showed that formation conditions of cronstedtite
seem to be compatible with those needed for hydrogenotrophic life, as previously supposed by other works.