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We demonstrate the use of elemental precursors Cu, Fe, Sn, and S to obtain a mawsonite (Cu6Fe2SnS8)/stannite (Cu2FeSnS4) composite using a solid-state process at ambient temperature in an industrial eccentric vibration mill for up to 240 min in argon atmosphere. The samples were characterized using various analytical techniques such as x-ray diffractometry, scanning electron microscopy, energy-dispersive x-ray spectroscopy, and nitrogen adsorption and magnetic measurements. For thermoelectric measurements, the properties of samples densified via spark plasma sintering were measured using standard methods needed to calculate the figure of merit. The transformation of elemental precursors to a composite mixture proceeds relatively rapidly via several intermediate steps. The kinetics of this transformation is also in good agreement with the results for the unconsumed sulfur content in the reaction mixtures and can also be correlated with the magnetization results. Based on the thermoelectric measurements of the sample milled for 240 min, the calculated figure of merit reached a value of zT = 0.51 at 623 K due to a very low lattice thermal conductivity of 0.29 W/m-K and moderate power factor of 3.3 μW/cm-K2. The thermoelectric results obtained for the material are comparable to previously published values for pure mawsonite prepared from elements by laboratory ball milling. [ABSTRACT FROM AUTHOR]