Summary Thermococcales, a major order of archaea inhabiting the iron‐ and sulfur‐rich anaerobic parts of hydrothermal deep‐sea vents, have been shown to rapidly produce abundant quantities of pyrite FeS 2 in iron–sulfur‐rich fluids at 85°C, suggesting that they may contribute to the formation of ‘low temperature’ FeS 2 in their ecosystem. We show that this process operates in Thermococcus kodakarensis only when zero‐valent sul...