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.
Highlights
According to the Commission on New Minerals, Nomenclature, and Classification of the InternationalMineralogical Association, 76 beryllosilicate minerals are currently known
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
The mineral assemblage of metamorphic rocks, exposed in the Wanni glacier area, which is located in the Binn Valley, Valais (Wallis), Switzerland, is unique and is the locality of eight rare-earth element (REE) arsenates and arsenites [35,36,37,38,39,40,41,42]
Summary
According to the Commission on New Minerals, Nomenclature, and Classification of the InternationalMineralogical Association, 76 beryllosilicate minerals are currently known. According to the Commission on New Minerals, Nomenclature, and Classification of the International. Layered (with infinite sheets of tetrahedra) structures are the most common: Almost 1/3 of beryllosilicates (27 out of 76) are represented by this structure type. Members of the gadolinite subgroup in the gadolinite supergroup form a big group within layered beryllosilicates (8 out of 27 minerals). According to the modern nomenclature [4], the general formula of the gadolinite supergroup is A2 MQ2 T2 O8 φ2 , where A = Ca, rare-earth element (REE) (Y and lanthanoides), Bi; M = Fe2+ ,. The monoclinic (P21 /c) structure of the gadolinite-supergroup minerals can be described as layered, consisting of two different layers parallel to (100) and alternating along the (100) direction.
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