Low-Temperature Crystal Chemistry of Hingganite-(Y), from the Wanni Glacier, Switzerland

Abstract

Hingganite from the Wanni glacier (Switzerland) was studied by means of energy dispersive and wavelength-dispersive spectroscopy, Raman spectroscopy, and low-temperature single-crystal X-ray diffraction. According to its chemical composition, the investigated mineral should be considered as hingganite-(Y). It showed a relatively high content of Gd, Dy, and Er and had limited content of lighter rare-earth element (REE), which is typical for Alpine gadolinite group minerals. The most intense Raman bands were 116, 186, 268, 328, 423, 541, 584, 725, 923, 983, 3383, and 3541 cm−1. Based on data of low-temperature [(−173)–(+7) °C] in situ single-crystal X-ray diffraction, it was shown that the hingganite-(Y) crystal structure was stable in the studied temperature range and no phase transitions occurred. Hingganite-(Y) demonstrated low volumetric thermal expansion (αV = 9(2) × 10−6 °C−1) and had a high thermal expansion anisotropy up to compression along one of the directions in the layer plane. Such behavior is caused by the shear deformations of its monoclinic unit cell.

Hydroxylherderite (Ca2Be2P2O8(OH)2) stability under extreme conditions (up to 750°C/100 GPa)

“…Among other studied gadolinite supergroup minerals under high‐temperature conditions, only gadolinite‐(Y), which does not contain (OH)‐groups, preserves its crystal structure at higher (1050°C) temperatures, 50 whereas datolite and “bakerite” undergo phase transition with the formation of HT‐okayamalite Ca 2 B 2 SiO 7 at about 720°C 48 . It should also be pointed out that hydroxylherderite demonstrates the most intense volume expansion ( α V = 37 × 10 −6 °C −1 ) among other gadolinite supergroup minerals ( α V = 9 × 10 −6 °C −1 for hingganite‐(Y), 27 × 10 −6 °C −1 for “bakerite” and gadolinite‐(Y) and 29 × 10 −6 °C −1 for datolite) 28,48,50 . Thus, the linear thermal expansion coefficient ( α V /3) for the gadolinite group minerals is 8 and is slightly lower than the average value for the whole borosilicate group (10 × 10 −6 °C −1 ) 100 …”

“…Nevertheless, there are no data on their behavior under extreme conditions. Only such gadolinite group minerals as datolite, hingganite‐(Y), and gadolinite‐(Y) were studied under high‐temperature and/or high‐pressure conditions 27,28,43–50 …”

Hellandite-(Y)–hingganite-(Y)–fluorapatite retrograde coronae: a novel type of fluid-induced dissolution–reprecipitation breakdown of xenotime-(Y) in the metagranites of Fabova Hoľa, Western Carpathians, Slovakia

“…Part of the bands in the region from 450 cm –1 to 650 cm –1 could be assigned to bending vibrations of the layer formed by (SiO 4 ) 4– and (BeO 4 ) 6– tetrahedra and were also detected in the spectra of macroscopic samples (Gorelova et al , 2020). Raman peaks at 969 cm –1 and 917 cm –1 (in the range of 969−992 and 906−917 cm –1 in the fitted spectra) are assigned to stretching vibrations of Si–O and Be–O in tetrahedral coordination (Škoda et al , 2018; Gorelova et al , 2020). The presence of a peak at 917 cm –1 correlates well with the fitted spectra of the macroscopic gadolinite samples.…”

“…Raman spectra of the investigated hingganite-(Y) were interpreted in context with published data, including that of isostructural datolite and gadolinite (Frost et al ., 2013; Goryainov et al , 2015; Thomas and Davidson, 2017; Škoda et al ., 2018; Paulmann et al , 2019; Gorelova et al , 2020; Tomašić et al , 2020) and were also compared with spectra of macroscopic gadolinite samples. Škoda et al (2018) assigned bands in the region of 200−750 cm –1 to bending modes of Si–O and Be–O, stretching vibrations of REE–O and Fe–O, as well as to lattice vibrations.…”

“…However, not all the bands can easily be attributed to Raman bands, according to the published data (Leite et al, 2001;Ńkoda et al, 2018;Gorelova et al, 2020). The Raman spectra of all the measured mineral phases, chemically corresponding to hingganite-(Y), are largely obscured by strong photoluminescence (PL) -both broad-and narrow-band.…”