ZnS-Na2S: The more reliable phase diagram belongs to the eutectic type with peritectic transformations (Figure 1.1) (Kopylov et al. 1978). The compounds Na6ZnS4 and Na2ZnS2 are melted incongruently at 820°C ± 5°C and 615°C ± 5°C correspondingly (Kopylov et al. 1978, Polyvyanny and Lata 1985). The eutectic composition and temperature are 54.5 mol. % (49 mass. %) Na2S and 605°C, respectively. Other compounds were not found in this system.