Pyrite (FeS2) thin films were synthesized using a H2S plasma to sulfurize hematite (Fe2O3) nanorods deposited by chemical bath deposition. The high S activity within the plasma enabled a direct solid-state transformation between the two materials, bypassing S-deficient contaminant phases (Fe1-xS). The application of plasma dramatically enhanced both the rate of conversion and the quality of the resulting material; stoichiometric FeS2 was obtained at a moderate temperature of 400 degrees C using a chalcogen partial pressure <6 X 10(-5) atm. As the S:Fe atomic ratio increased from 0 to 2.0, the apparent optical band gap dropped from 2.2 (hematite) to similar to 1 eV (pyrite), with completely converted layers exhibiting absorption coefficients >10(5) cm(-1) in the visible range. Room-temperature conductivity of FeS2 films was on the order of 10(-4) S cm(-1) and approximately doubled under calibrated solar illumination.