Organics formation mediated by different [Ni-]FeS minerals. Screening of various minerals in the glass cell reactor indicated that FeS, Ni-FeS, and FeS2 all produced short chain carboxylic acids in μM concentrations on the ocean side of the reactor at 25˚C (Table , entries 1-3), while none was detected on the vent side (Table , entry 4). This suggests that rather than gases or organic molecules passing between chambers, that there is instead an indirect electrochemical mechanism whereby H2 is oxidized on the 'vent' side of the reactor, electrons pass through the mineral, and reduce organics on the 'ocean' side of the reactor. Single-pot blank reactions-[Ni-]FeS minerals with CO2 gas (Table , entry 5), and no mineral with CO2 and H2 (Table , entry 6)-offered neither formic acid nor acetic acid. This suggests that under ambient temperature (~22-25°C) and anoxic condition the mineral cannot be significantly sacrificially oxidized as the source of electrons for CO2 fixation, and nor can CO2 & H2 together effect such reactions in the absence of an electrocatalyst.