Redefinition of satimolite

Abstract

The borate mineral satimolite, which was first described in 1969 and remained poorly-studied until now, has been re-investigated (electron microprobe analysis, single-crystal and powder X-ray diffraction studies, crystal-structure determination, infrared spectroscopy) and redefined based on the novel data obtained for the holotype material from the Satimola salt dome and a recently found sample from the Chelkar salt dome, both in North Caspian Region, Western Kazakhstan. The revised idealized formula of satimolite is KNa2(Al5Mg2)[B12O18(OH)12](OH)6Cl4·4H2O (Z = 3). The mineral is trigonal, space group R$\bar{3}$m, unit-cell parameters are: a = 15.1431(8), c = 14.4558(14) Å and V = 2870.8(4) Å3 (Satimola) and a = 15.1406(4), c = 14.3794(9) Å and V = 2854.7(2) Å3 (Chelkar). The crystal system and unit-cell parameters are quite different from those reported previously. The crystal structure of the sample from Chelkar was solved based on single-crystal data (direct methods, R = 0.0814) and the structure of the holotype from Satimola was refined on a powder sample by the Rietveld method (Rp = 0.0563, Rwp = 0.0761 and Rall = 0.0667). The structure of satimolite is unique for minerals. It contains 12-membered borate rings [B12O18(OH)12] in which BO3 triangles alternate with BO2(OH)2 tetrahedra sharing common vertices, and octahedral clusters [M7O6(OH)18] with M = Al5Mg2 in the ideal case, with sharing of corners between rings and clusters to form a three-dimensional heteropolyhedral framework. Each borate ring is connected with six octahedral clusters: three under the ring and three over the ring. Large ellipsoidal cages in the framework host Na and K cations, Cl anions and H2O molecules.

Refinement of the crystal structure of fresnoite, Ba2TiSi2O8, from Löhley (Eifel district, Germany); Gladstone–Dale compatibility, electronic polarizability and vibrational spectroscopy of minerals and inorganic compounds with pentacoordinated TiIVand a titanyl bond

“…However, a titanyl bond was also found in several titanosilicates of alkaline elements. One of them is natisite, tetragonal Na 2 TiSiO 5 , in which the Ti-O apex distance is equal to 1.696 (3) A ˚ (Pekov et al, 2021). Earlier, practically the same value [1.695 (5) A ˚] was reported for the Ti-O apex distance in the synthetic analogue of natisite (Nyman et al, 1978).…”

“…It was shown that titanium occupies a site with fivefold coordination (square pyramid) with one short Ti-O distance of 1.63 (5) A ˚(titanyl bond) and four Ti-O bonds of 2.00 (2) A ˚. However, it was shown recently that the distance of 1.634 A ˚deviates from the correlation between the shortest Ti-O bond distances in the TiO 5 polyhedra and frequencies of corresponding stretching vibrations (Pekov et al, 2021). Based on this fact and taking into account large values of the R factor of the crystal structure refinement and the error with determination of the Ti-O distances, we supposed that the value of 1.634 A ˚for the shortest Ti-O bond may be incorrect.…”

Dmitryvarlamovite, Ti2(Fe3+Nb)O8, a new columbite-supergroup mineral related to the wolframite group

“…3) was obtained in order to confirm the absence of OH groups. In the range of 360-1500 cm -1 , the spectrum is close to those of other partly disordered niobium members of the columbite supergroup, including rossovskyite (Konovalenko et al, 2015), samarskite-(Y) (Chukanov and Vigasina, 2020) and nioboixiolite-(Mn 2+ ) (Chukanov et al, 2023b). Bands in the IR spectra of these minerals are poorly resolved because of mixed occupancies of cation sites.…”

Okruginite, Cu2SnSe3, a new mineral from the Ozernovskoe deposit, Kamchatka peninsula, Russia

“…This deposit is distinguished by a variety of selenide and telluride minerals, including some new and unnamed species (Kovalenker and Plotinskaya, 2005; Spiridonov et al ., 1990; 2009; 2014; Okrugin et al ., 2022) as well as the recently described minerals ozernovskite (Pekov et al ., 2021) and rudolfhermannite (Pekov et al ., 2022).…”