Hydrothermal Fe-Si oxide deposits are ubiquitous in the hydrothermal vent sites at mid-ocean ridge and back-arc seafloor spreading centers. According to the recognitions of micron-scale filamentous textures and the results of molecular biology, neutrophilic Fe-oxidizing bacteria including Gallionella ferruginea, Leptothrix ochracea and the novel Mariprofundus ferrooxydans (PV-1 Strain) are considered to have a significant role in the formations of Fe-Si oxides deposits of the hydrothermal systems. These bacteria are capable of autotrophic metabolism with Fe²⁺as the sole electron donor,  increas the rate of Fe²⁺oxidation, and  then get energy for their growth. Electrostatic attraction along with the organic functional groups lead to the precipitations of iron oxides on the surface of abundant filamentous microbial structure that closely resemble the morphology of the Fe-oxidizing bacteria. Then the filaments were combined together to form a three-dimensional network. Novel observations were made of the Fe-Si framework of the network revealing the composite structure of Fe-rich filamentous in the core and the pure opal crust in the outer to form the “two-generation structure”. This indicates that the large-scale silica precipitation caused by conductive cooling  often takes place after the construction of the network. Recent studies about the Banded Iron Formations (BIF)  considered to be the analog of modern hydrothermal Fe-Si deposits  indicate an ancient hydrothermal origin for the iron. Moreover, owing to the pervasive anoxic state when the BIFs formed, the photosynthetic organisms for instance,  cyanobacteria  and the neutrophilic Fe-oxidizing bacteria are proposed to be involved in the ancient BIFs formations. 