CRYSTAL-CHEMISTRY AND IR SPECTROSCOPY OF CL- AND SO4-BEARING CANCRINITE-LIKE MINERALS

Cl- and SO4-bearing cancrinite-like minerals from Italian localities w ere studied by means of EPMA, X-ray diffraction, and IR spectroscopy t o relate their chemical composition, IR data, and structural features. The framework of the cancrinite-like minerals consists of six-membere d rings of aluminosilicate tetrahedra stacked along c. Six types of su bunits resulting from different stacking sequences can be identified: free channel, cancrinite, sodalite, losod, liottite, and giuseppettite cages. The free channel is possible only with an AB sequence; in fact , the insertion of a C layer interrupts the channel forming the variou s cages. The occurrence of these structural subunits seems to correspo nd to the different chemistries of the cancrinite-like minerals, espec ially their anion content. According to this model, the SO4 group seem s to play a major role. With the exception of giuseppettite, it tends to fill completely the available voids within the frameworks.