Junoite, Cu2Pb3Bi8(S,Se)16, (S:Se = 5:1), is monoclinic, space group C2m with a = 26.66(1), b = 4.06(1), c = 17.03(1) Å and β = 127.20(2)°. Diffractometer data were recorded with an equi-inclination diffractometer equipped with a proportional counter; the structure was solved using the Patterson method. Least squares refinement reduced the R value to 11.0 percent and permitted distinction of Pb and Bi on the basis of bond distances. The asymmetric unit of the unit cell contains 2 Pb, 4 Bi, 1 Cu, and 8 S atoms. The lead atom at the origin has octahedral coordination, while the other lead atom has eight-fold coordination. Three of the bismuth atoms have three sulfur neighbors at distances ranging from 2.51 to 2.89 Å while there is evidence for selenium ordering in the structure which results in larger than average bonding distances in the fourth Bi(S,Se)3 group. Copper has distorted tetrahedral coordination with bonds ranging from 2.32 to 2.52 Å in length.
A survey of dimensions of the BiS3, anionic group in bismuth sulfosalts is also reported; average lengths of Bi-S non-bridge bonds and S-Bi-S bridge bonds were found to be 2.63 and 2.76 Å, respectively.
Junoite and other bismuth sulfosalts can be successfully classified on the basis of the dimensional relationship between the coordination polyhedra around the monovalent and divalent atoms, and the coordination polyhedra. around the trivalent atoms (Takeuchi and Sadanaga's 1969 system of classification).