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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.

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Keplerite is a new mineral, the Ca-dominant counterpart of the most abundant meteoritic phosphate, merrillite. The isomorphous series merrillite-keplerite, Ca 9 NaMg(PO 4 ) 7 -Ca 9 (Ca 0.5 □ 0.5 )Mg(PO ) 7 represents the main reservoir of phosphate phosphorus in the Solar System. Both minerals are related by the heterovalent substitution at the B-site of the crystal structure: 2Na + (merrillite) → Ca 2+ + □ (keplerite). The near-end-member keplerite of meteoritic origin occurs in the main-group pallasites and angrites. The detailed description of the mineral is made based on the Na-free type material from the Marjalahti meteorite (the main group pallasite). Terrestrial keplerite was discovered in the pyrometamorphic rocks of the Hatrurim Basin in the northern part of Negev desert, Israel. Keplerite grains in Marjalahti have an ovoidal to cloudy shape and reach 50 μm in size. The mineral is colorless, transparent with a vitreous luster. Cleavage was not observed. In transmitted light, keplerite is colorless and non-pleochroic. Uniaxial (−), ω 1.622(1), ε 1.619(1). Chemical composition (electron microprobe, wt.%): CaO 48.84; MgO 3.90; FeO 1.33; P 2 O 5 46.34, total 100.34. The empirical formula (O = 28 apfu) is: Ca 9.00 (Ca 0.33 Fe 2+ 0.20 □ 0.47 ) 1.00 Mg 1.04 P 6.97 O 28 .The ideal formula is Ca 9 (Ca 0.5 □ 0.5 )Mg(PO 4 ) 7 . Keplerite is trigonal, space group R3c, unit-cell parameters refined from single-crystal data are: a 10.3330(4), c 37.0668(24) Å, V 3427.4(3) Å 3 , Z = 6. The calculated density is 3.122 g cm -3 . The crystal structure has been solved and refined to R 1 = 0.039 based on 1577 unique observed reflections [I >2σ(I)]. A characteristic structural feature of keplerite is a partial (half-vacant) occupancy of the sixfold-coordinated B-site (denoted as CaIIA in the earlier works). The disorder caused by this cation vacancy is the most likely reason for the visually resolved splitting of the ν 1 (symmetric stretching) (PO 4 ) vibration mode in the Raman spectrum of keplerite. The mineral is an indicator of high-temperature environments characterized by extreme depletion of Na. The association of keplerite with "REE-merrillite" and stanfieldite evidences for the similarity of temperature conditions occurred in the Mottled Zone to those This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America.The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.

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