TEM-EELS study of natural ferrihydrite from geological–biological interactions in hydrothermal systems

In this study, we have investigated the mineralogy present on the scaphognatite of the Rimicaris exoculata shrimp collected at a Mid-Atlantic Ridge hydrothermal vent. The structure, morphology and impurities of the minerals were analyzed by transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). The main minerals observed were clusters of iron oxides found attached to the bacterial cells present on the setae of the scaphognatite. Structural investigations based on high-resolution electron microscopy and electron diffraction affirm that these clusters are composed of two-line ferrihydrite. The EELS measurements demonstrate that the ferrihydrite is bearing a mixed valence iron distribution and P, Si, Ca, N and Ni ions at impurity levels. The stability of this uncommon phase is then discussed based on work previously reported in literature for analogous poorly ordered iron oxides.