Haüyne: mutual cations/anionic groups arrangement and thermal expansion mechanism

摘要: The paper reports a crystal chemical investigation of hauyne sample, \( ({\rm Na}_{4.4}{\rm K}_{1.1}{\rm Ca}_{2.1}) _{\Sigma_{7.6}} [{\rm Si}_6{\rm Al}_6{\rm O}_{24}]\)(SO4)1.6(S3)0.3(CO2)0.1, from Sacrofano, Italy, conciliating spectroscopic, chemical, and room temperature (RT) X-ray single-crystal diffraction data. RT structure refinement provides detailed description the extra-framework cations anionic groups mutual arrangement. occurrence minor amounts S3− poly-sulphur radical, responsible light-blue colour revealed by Raman spectroscopy, has been shown to play an important role in modifying cation partition among three sites: M1, M2, M3. Moreover, traces enclathrated CO2 were FTIR. Besides, thermal behaviour investigated, up 1,098 K, situ HT-XRPD. Results indicate relevant differences with respect reference sample at shows weak satellite reflections that disappear 673 K. As expected, geometry rigid TO4 tetrahedra is independent temperature, whereas framework expands decreasing angle rotation both SiO4 (φSi) AlO4 (φAl) as function temperature. quadric dependence φSi φAl ends 973 correspondence angles ca. 3°, indicating attainment nearly full expansion framework. At temperatures exceeding such value, only tetrahedral acts. result mechanism, a-parameter change regime Such model similar, albeit non-identical, several cancrinite–sodalite group minerals.