Crystal Chemistry, Isomorphism, and Thermal Conversions of Extra-Framework Components in Sodalite-Group Minerals

Isomorphic substitutions of extra-framework components in sodalite-group aluminosilicate minerals and their thermal conversions have been investigated using infrared, Raman, electron spin resonance (ESR), as well as ultraviolet, visible and near infrared (UV-Vis-near IR) absorption spectroscopy methods and involving chemical and X-ray diffraction data. Sodalite-related minerals from gem lazurite deposits (hauyne, lazurite, and slyudyankaite) are characterized by wide variations in S-bearing extra-framework components including SO42- and various polysulfide groups (S-2(?-), S-3(?-), S-4(?-) radical anions, and S-4 and S-6 neutral molecules) as well as the presence of CO2 molecules. Heating at 700 degrees C under reducing conditions results in the transformation of initial S-bearing groups SO42- and S-3(?-) to a mixture of S2-, HS-, S-2(?-), and S-4(?-) and transformation of CO2 to a mixture of CO32- and C2O42- or HC2O4- anionic groups. Further heating at 800 degrees C in air results in the decomposition of carbonate and oxalate groups, restoration of the SO42- and S-3(?-) groups, and a sharp transformation of the framework. The HS- anion is stable only under reducing conditions, whereas the S-3(?-) radical anion is the most stable polysulfide group. The HS--dominant sodalite-group mineral sapozhnikovite forms a wide solid-solution series with sodalite. The conditions required for the formation of HS-- and CO20-bearing sodalite-group minerals are discussed.

Automated summary

This study investigated the isomorphic substitutions and thermal conversions of extra-framework components in sodalite-group aluminosilicate minerals. Various spectroscopy methods were used, including infrared, Raman, electron spin resonance, and UV-Vis-near IR absorption spectroscopy. The results showed that sulfur-bearing groups and CO2 molecules in the minerals undergo transformations during heating processes.