The presence of nanoparticulate pyrite is reported in hydrothermal emissions from Rainbow, TAG and Snakepit on the Mid- Atlantic Ridge (MAR). When coupled with previously collected data from East Pacific Rise 9 °N (EPR) and Lau Basin, these data demonstrate that pyrite nanoparticles are a widespread component of black smoker emissions from hydrothermal vents and are found in significant concentrations at a fast spreading mid-ocean Ridge (EPR), a back- arc basin (Lau Basin), and a slow spreading mid- ocean Ridge (MAR). The maximum percentage of filtered iron emitted as nanoparticulate pyrite was found to be as high as 25%, 10%, and 5%, respectively. As a widespread component of hydrothermal vent emissions, these nanoparticles may be an important source of iron to the world’s oceans. Metals such as Cu and Zn are detected in pyrite- containing aggregates at all sites, and chalcopyrite was a component of nanoparticle aggregates at MAR. Iron containing silicate nanoparticles are also identified, and indicate that nanoparticles other than sulfides should also be considered when determining transport implications of hydrothermal vent emissions. The varied morphologies and the presence of different minerals within these nanoparticles provide insight into their formation and stability.