CONTRIBUTIONS TO THE CRYSTAL-CHEMISTRY OF THALLIUM SULFOSALTS - IV - MODULAR DESCRIPTION OF TL-AS-SB SULFOSALTS REBULITE AND JANKOVICITE

On modular level the crystal structures of TI-As-Sb sulfosalts jankovi cite (LIBOWITZKY et al. 1995) and rebulite (BALIC-ZUNIC et al. 1982) a re composed of (210) layers of SnS archetype, alternatively one and tw o coordination pyramids thick. These layers are joined by layers with mirror symmetry which contain Sb/As pyramids and TlS8 cubes. Variable thickness of SnS-like layers yields hypothetical homologous series. Pe riodic twinning of SnS-like layers on (101)(SnS) alters the jankovicit e structure into the rebulite structure. This twinning does not have O D character. The OD layers (100) of jankovicite have idealized symmetr y A (1) 2/m 1, interlayer elements are {(1) 2(1/2)/a(2) 1}. Besides th e observed polytype P (1) over bar another maximally ordered variant, A 2/m is possible. It remains unobserved, probably due to desymmetriza tion of OD layers. The complex rings and spirals of BS3 and BS4 polyhe dra (B = As, Sb) are centered on SnS-like layers. They are not vehicle s for accommodation of Ione electron pairs.