Structural dissymmetrization of optically anisotropic Grs_64±1Adr_36±1Sps₂grandite from Meka Presedla (Kopaonik Mt., Serbia)

Abstract

In this paper, grandite core with Grs64±1Adr36±1Sps2 composition was crystallographically studied. This core represents zone A of the macroscopically visible five A–E zones of the optically anisotropic Grs58–64Adr36–42Sps2 grandite. The applied procedure includes the detailed analysis of the powder diffraction patterns, and the Rietveld refinements of the crystal structures in a series of 18 space groups and two mixtures, which were followed by the comparative analysis of the R-values, site occupancy factors, and the bond lengths and angles. Synthesis of all of the presented results allows us to undoubtedly conclude that studied grandite is not cubic, neither as monophase nor as multiple phases in a mixture. Namely, it was established that structural dissymmetrization occurred and that it crystallized in the disordered rhombohedral $R\bar{3}c$ or orthorhombic Fddd space groups, whereby the first one is more probable. Beside the established lower symmetry of the studied grandite, which could be treated as the primary cause, the residual strain is also not excluded as the second possible cause for its slight optical anisotropy.

A possible connection between phosphate tungsten bronzes properties and Briggs-Rauscher oscillatory reaction response

“…Furthermore, it was previously shown that various tilting and orientations of the polyhedrons and polyhedral chains in other phosphate tungsten bronzes could derive the different space groups of crystallization [5], which makes this problem very complex from the structural aspect. The similar observations were also confirmed in our studies of other materials [38,39]. Although crystal structure refinements were beyond of the scope of this paper, different calculated crystallographic axis and angles between PWB, Li-PWB, and Ca-PWB (Table II) could be sufficient proof of the various tilting of their WO 6 octahedrons and PO 4 tetrahedrons.…”

Trigonal variation in the garnet supergroup: the crystal structure of nikmelnikovite, Ca12Fe2+Fe3+3Al3(SiO4)6(OH)20, from Kovdor massif, Kola Peninsula, Russia

“…It should be noted that low-symmetry birefringent garnets have been observed and studied previously (Shtukenberg et al , 2005; Frank-Kamenetskaya et al , 2007). A comprehensive review of the relevant literature was provided recently by Tančić et al (2020). However, nikmelnikovite is the first distinct garnet-supergroup member with a trigonal symmetry.…”

Characterisation, axial anisotropy, and formation conditions of celestine minerals from the Jabal Eghei (Nuqay) late Neogene – Pleistocene volcanic province, southeastern edge of the Sirt Basin, southern Libya: Constraints on the mineralogical geothermometer

“…(v) The option that various structural variations within the samples could take place Although the crystal structure refinements are beyond the scope of this paper, our previous studies of diverse mineral species and solid solutions, have demonstrated that the different UCPs, polyhedral distortions, site occupancy factors, bond lengths, bond angles and valence units, could be influenced either by: (1) different inserted cations into the mineral structure; and/or by ( 2) diverse conditions of their formation, in particular, the temperature and pressure (Tančić 2017(Tančić , 2018Tančić and Kremenović, 2022;Tančić et al, 2012Tančić et al, , 2020Tančić et al, , 2023.…”