It has been found that in addition to the Ag6S3O4 phase discovered earlier, the reaction between Ag2SO4 and Ag2S in the solid state leads to a phase having the formula Ag8S4O4. This phase can be obtained by heating in air a mixture comprised initially of Ag2SO4 (25.0 mol%) and Ag2S (75.0 mol%), Ag8S4O4 melts at 400 degrees C. In air, the melt starts decomposing immediately. The final solid product of Ag8S4O4 decomposition is metallic silver. In inert atmosphere, thermal decomposition of the melt starts at 445 degrees C and the final solid products of the decomposition are silver sulfide and metallic silver. Ag8S4O4 phase crystallizes in a monoclinic system and has the following unit-cell parameters: a = 1.42669 nm, b = 0.65824 nm. c = 1.05039 nm, beta = 91.32 degrees, Z = 4, V = 0.98617 nm(3), and d(x) = 7.10 g/cm(3).