Structure Modulations and Symmetry of Lazurite-Related Sodalite-Group Minerals

Abstract

Lazurite and other lazurite-related minerals (LRMs) containing sulfur in both sulfate and sulfide forms are sodalite-type compounds with various extraframework species, of which the tendency to order leads to structural modulations with a period that is either commensurate or incommensurate with the period of the basic lattice. In this work, the structures of incommensurately modulated monoclinic LRMs are re-examined based on the superstructure of slyudyankaite, formerly known as triclinic lazurite. Similarities and differences between three one-dimensionally modulated LRMs and cubic LRM structures modulated in several directions are discussed. Assumptions are made on how the symmetry of the structure and the composition of the crystal can affect the period of structural modulation.

Photochromism, UV-Vis, Vibrational and Fluorescence Spectroscopy of Differently Colored Hackmanite

“…The peak at 294 cm −1 is caused by the symmetric Al/Si-tetrahedra bending, and the peak at 463 cm −1 is caused by the Na4Cl-tetrahedra stretching, Si-O bending, SiO4 vibration or ν of T-O-T; 987 cm −1 represents the A1 stretching frequency of ν1 of sodalite framework or the symmetric Al/Si-tetrahedra stretching. The literature suggests that the peak at 987 cm −1 may also be caused by the oxygen bending mode A1 or the symmetric stretching vibration of A1(ν1)SO4 2-; 1062 cm −1 is caused by asymmetric Al/Si-tetrahedra stretching and is also the main energy band of CO3 2- [17,25,[30][31][32].…”

“…Structure and Composition CharacteristicsThe crystal structure of the tetrahedral framework SOD ([Al 6 Si 6 O 24 ] 6− ) with large cavities (β cages) within the structure can accommodate large cations such as Na + , K + , and Ca 2+ and additional anions such as Cl − , F − , SO 4 2− , S 2− , S 3− , CO 3 2− , OH −[18]. As shown in Figure4, the absorption peak at 1008 cm −1 is due to the asymmetric stretching vibration of Si-O-Si, and its wave number changes due to the difference of Si/Al in the framework[19][20][21]; 734, 709, and 665 cm −1 correspond to the vibrational peaks of the symmetric Si-O-Si, and another study suggests that 709 cm −1 corresponds to the bending vibration of the chemical bonding in the O-Al-O unit due to the Al-induced chemical bond bending vibrations; 665 cm −1 is caused by Al-O vibrations, and the peaks at 474 and 439 cm −1 belong to the bending vibrations of T-O-T (T = Si/Al)[8,[22][23][24][25][26][27][28][29][30].Crystals 2023, 13, x FOR PEER REVIEW 5 of 12…”