Tin is regarded as forming two sulphides, the monosulphide, which is known to mineralogists as herzenbergite, and the disulphide which is mineralogically unknown but commercially utilized as "mosaic gold." Both of these sulphides have been synthesized in this study, as likewise a third sulphide of intermediate composition. This third sulphide or sesquisulphide is probably Sn 2 S 3 or SnS.SnS 2 .Heretofore, the system tin-antimony-sulphur had been investigated but in part, and inaccurately. This investigation has disclosed two compounds of SnS with Sb 2 S 3 , namely phase A, SnS.Sb 2 S 3 and phase B, 3 SnS.Sb 2 S 3 . No compound was found of SnS 2 with Sb 2 S 3 , but a characteristic compound of SnS, SnS 2 and Sb 2 S3 was obtained. The formula of this phase is not perfectly settled, but is perhaps 4 SnS.Sn 2 S 3 .Sb 2 S 3 . No natural minerals have been described in this system.Tin and lead sulphides are supposed to form one compound, teallite, whose formula is variously given as PbS.SnS and PbS.SnS 2 . This compound could not be synthesized. Instead it was found that SnS and Sn 2 S 3 dissolve in solid solution large quantities of lead sulphide.