Life proliferates almost everywhere on Earth but determining whether or not hyperthermophile microorganisms have colonised a given hydrothermal environment, such as black smoker chimneys, remains challenging. Some mineral phases like pyrite spherules have been proposed to possibly serve as biosignatures. Yet, little is known about the specificities of pyrites produced via abiotic processes under hydrothermal conditions, making these pyrite spherules only potential biosignatures at best. Here, we report results of abiotic syntheses of pyrites under conditions reproducing those existing in the chimneys of black smokers, in the presence or in the absence of various organic compounds. We experimentally show that no pyrite is produced in the absence of organic material, whereas the chemical nature of the organic compounds controls the shape and crystallinity of the pyrite produced. The presence of complex organic matter, here compounds derived from lysed cells, appears necessary for the production of pyrite spherules previously described as biogenic, suggesting that the pyrite spherules detected in natural black smokers may not be considered as biogenic stricto sensu, but rather as proxies of the presence of microorganisms.