Zinc-iron sulphide mineralization in tubes of hydrothermal vent worms

Nanocrystalline zinc-iron sulphide minerals were found within tubes of Alvinella pompejana, collected at 9 degreesN on the East Pacific Rise, in a preliminary study carried out by conventional analytical transmission electron microscopy. Their structure is consistent with either the sphalerite or wurtzite polymorphs of ZnS. In contrast with sulphides usually observed in deep-sea hydrothermal environments, the unique sulphide observed within the exoskeleton of the pompeii worms has a (Zn0.88Fe0.12)S composition. The zinc-iron sulphide nanocrystals are grouped in submicrometer-sized clusters which form layers, concentrically to the proteinaceous tube axis. This is the first characterization of minerals precipitated within a biological matrix from hydrothermal vents organisms. These minerals represent a new example of zinc-iron biologically induced mineralization. Such layers of nanocrystalline zinc-iron sulphide minerals could be used as valuable markers of annelid tubes, in the growing field of studies focusing on fossilized paleo-hydrothermal vent systems.