Atomic arrangements around the O3 site in Al- and Cr-rich oxy-tourmalines: a combined EMP, SREF, FTIR and Raman study

Abstract

A study of natural oxy-tourmalines belonging to the system oxy-dravitechromo-alumino-povondraiteoxy-chromium-dravite from the Sludyanka crystalline complex (Southern Baikal region, Russia) was carried out to explore the characteristic vibrational bands in the principal (OH)-stretching frequency and their relations to the O3 Revised Manuscript Click here to download Manuscript: Cr-tm_IR ms O3_R1.docx Click here to view linked References 2 anion site of the tourmaline structure. Relevant information was obtained using electron microprobe analysis (EMPA), structural refinement (SREF), infrared (IR) and Raman single crystal spectroscopy. The studied oxy-tourmalines are characterized by the substitution Al ↔ Cr which is accompanied by redistribution of Mg over the Y and Z sites. The occurrence of strong correlations between relative peak area intensities for two IR bands at 3565 and 3519 cm-1 and cation site populations derived from SREF and EMP data allowed assignment of the band at 3565 cm-1 to the cluster [ Y Mg Z Al Z (Al,Mg)]-O3 and the band at 3519 cm-1 to the cluster [ Y Cr Z (Cr,Al) Z (Cr,Al,Mg))]-O3. It appears that the combination of polarized IR and Raman spectra collected with the electric vector E  c and E // c may provide a useful characterization of the local (OH) environments around the O3 site of the tourmaline structure.

Magnesio-lucchesiite, CaMg3Al6(Si6O18)(BO3)3(OH)3O, a new species of the tourmaline supergroup

“…Spectra were collected parallel (E||E) and perpendicular (E||O) to the c-axis, over the wavenumber range 2000-13000 cm -1 , with a resolution of 4 cm -1 during 64 cycles. In the spectrum of sample #1, bands above 3650 cm -1 , associated with (OH)groups at the O(1) site (e.g., Gonzalez-Carreño et al 1988;Skogby et al 2012;Bosi et al 2015), are very weak and consistent with the low content of (OH) at the O(1) site reported in the empirical formula (see below). In sample #2 the greater magnitude of the bands above 3650 cm -1 are consistent with minor occurrence of (OH) at O(1) as reported in the empirical formula (see below).…”

Crystal structure and Raman spectroscopic studies of OH stretching vibrations in Zn-rich fluor-elbaite

“…). The refined X-site occupancy [<X-O> = 2.685(1) Å], corresponding to the presence at the site 0.821(6) Na apfu, agrees within 2 sd with the occupancy Although Raman and IR studies of tourmalines refer usually to the Si 6 O 18 rings, BO 3 groups and OH groups, all previous researchers agree that the O-H stretching vibrations in the range 3000-4000 cm -1 , carry the highest portion of crystal chemical and structural information(Gonzalez- Carreño et al 1988, Hoang et al 2011 Skogby et al 2012;Zhao et al 2012;Fantini et al 2014;Bosi et al 2015Bosi et al , 2016Berryman et al 2016;Kutzschbach et al 2016; Watenphul et al 2016a;Mercurio et al 2018;Bronzova et al 2019). This is a result of the specific location of the V OH and W OH groups in the tourmaline structure because the ligands are bonded to the octahedrallycoordinated occupants of the Y-and Z-sites, which are the two sites with the highest diversification in cation populations.…”

Thermal stability of extended clusters in dravite: a combined EMP, SREF and FTIR study

“…1) and the band at ~3620 cm −1 (Fig. 3), may be related to the short-range arrangement X (Na)-W (OH)-(MgMgR 3+ ) and X (□)-W (OH)-Y (MgAlAl) (Bosi et al 2015b;Berryman et al 2015). Note that the local arrangement W (OH)-Y (MgAlAl) is expected to be unstable from a bond-valence perspective (e.g., Hawthorne 2002), but it could became stable at high temperatures (T > 800 °C).…”