Rock-Forming Sodalite–Sapozhnikovite Series Feldspathoids from the Lovozero Alkaline Complex (Kola Peninsula, Russia): Isomorphism, Thermal and Radiation-Induced Transformations, and Genetic Mineralogy

Sulfur-enriched sodalite-group feldspathoids from the Lovozero alkaline complex (Kola Peninsula, Russia) and products of their laboratory, anthropogene, and natural thermal and radiation-induced transformations have been studied by electron-probe nicroanalysis, single-crystal X-ray diffractometry, Raman, infrared, and electron spin resonance spectroscopy, and ultra-violate, visible, and near-infrared absorption spectroscopy. Sodalite Na8Al6Si6O24Cl2 and sapozhnikovite Na8Al6Si6O24 (HS) 2 form an almost continuous, isomorphous series in highly agpaitic feldspathoid syenites and their pegmatites with the Cl: HS ratio ranging from Cl100 (HS) 0 to Cl12 (HS) 88 (mol %) ]. In the Lovozero complex, the HS– hydrosulfide anion has turned out to be the major form of the sulfidic sulfur occurrence in minerals of this group, including sodalite–hackmanite. It has been found that sapozhnikovite and the HS-rich sodalite phase transition to it are important rock-forming minerals of some rocks of this complex, including a new highly alkali rock named poikilitic nepheline–sapozhnikovite syenite. Sapozhnikovite and intermediate members of the sodalite–sapozhnikovite series are the sensitive geochemical oxymeter indicator, which points out the reducing conditions of the mineral formation. Upon heating, the HS– anion in the sodalite–sapozhnikovite series minerals destroys and sulfur passes to the polysulfide with the formation of, first, the S₂^{ - } radical anion (500–600°C) and, then, the S₃^{ - } radical anion (700°C and higher). The S₃^{ - } groups also appear at the radiation-induced transformation of these minerals. Under the natural radioactive irradiation, at the contact with Th-enriched steenstrupine, an intermediate member of the sodalite–sapozhnikovite series transformed to the S₃^{ - } rich sodalite variety with the simplified formula Na8Al6Si6O24Cl, (S3) earlier unknown in nature.