Re-examination of the tintinaite-kobellite series has shown that tintinaite contains 2.1 wt. % Cu and has the formula Pb (sub 10.6) Sb (sub 15.3) Cu (sub 1.8) Ag (sub 0.2) S (sub 34.5) (D 5.65 g/cm 3 ), or, more simply, Pb 11 Sb 15 Cu 2 S (sub 34.5) . Miehe's (1971) structural formula for kobellite has been re-examined; we conclude that Fe and Cu in tintinaite-kobellite have different structural roles; incorporation of Cu is envisaged as following the scheme (Bi,Sb) (super 3+) --> Pb (super 2+) + Cu (super +) , thus implying a mixed Pb-(Bi,Sb) site. Jamesonite and robinsonite coexisting with tintinaite are devoid of Cu; associated epitactic growths of "mineral JC" (Pb 2 CuSb 3 S 7 ) on jamesonite suggest that each 6-coordinated Fe atom in jamesonite was replaced by two Cu atoms with 4-fold coordination. "Mineral JC" is a low-temperature phase derived by alteration in which both jamesonite + tintinaite contribute essential elements. Minor amounts of Cu incorporated in a specific tetrahedral site is thought to stabilize some Pb sulfosalts at low temperatures; examples are meneghinite, tintinaite, and probably also launayite Pb 10 Sb,As) 12 CuS 30 and sorbyite Pb 9 Sb 9 As 2 CuS 26 .--Modified journal abstract.