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Single crystals of two new intermetallic phases Sm 2 Mn 1- x Ga 6- y Ge y ( x = 0.1-0.3, y = 0.6-1.0) and Sm 4 MnGa 12- y Ge y ( y = 3.0-3.5) were grown using a self-flux technique. According to single crystal X-ray diffraction data, Sm 4 MnGa 12- y Ge y is characterised by the Y 4 PdGa 12 structure type ( a ∼ 8.65 Å; Im 3̄ m ), while Sm 2 Mn 1- x Ga 6- y Ge y formally adopts the K 2 PtCl 6 structure type ( a ∼ 8.71 Å; Fm 3̄ m ). The general features of both compounds with rather similar crystal structures are represented by the alternation of empty and Mn-filled p-element octahedra, the order of which is determined by the Mn concentration. The diffraction data for Sm 2 Mn 1- x Ga 6- y Ge y reveal a large concentration of Mn vacancies ( x ∼ 0.3), which affects adjacent Ga/Ge atoms leading to their shift towards the vacancy. Both compounds demonstrate two ferromagnetic-like transitions and the presence of two interacting Mn and Sm magnetic sublattices. The Mn sublattice orders at T C1 of 143 K and 318 K, while the Sm one orders at lower temperatures at T C2 of 50 K and 280 K for Sm 4 MnGa 8.6 Ge 3.4 and Sm 2 Mn 0.74 Ga 5.1 Ge 0.9 , respectively. The increase in Mn content not only increases the ordering temperatures, but also dramatically decreases the coercivity μ 0 H C from 230 mT to just 6.5 mT at 2 K. Despite the presence of two magnetically active sublattices in Sm 2 Mn 0.74 Ga 5.1 Ge 0.9 , the magnetic entropy change is quite low and only reaches 0.3 J kg -1 K -1 at T = 300 K and μ 0 H = 5 T, while the estimated relative cooling power (RCP) is about 36 J kg -1 at 5 T.

β-Tricalcium phosphate (β-TCP) is widely used as bone implant material. It has been observed that doping the β-TCP structure with certain cations can help in combating bacteria and pathogenic microorganisms. Previous literature investigations have focused on tricalcium phosphate structures with silver, copper, zinc, and iron cations. However, there are limited studies available on the biological properties of β-TCP containing nickel and cobalt ions. In this work, Ca 10.5- x Ni x (PO 4 ) 7 and Ca 10.5- x Co x (PO 4 ) 7 solid solutions with the β-Ca 3 (PO 4 ) 2 structure were synthesized by a high-temperature solid-state reaction. Structural studies revealed the β-TCP structure becomes saturated at 9.5 mol/% for Co 2+ or Ni 2+ ions. Beyond this saturation point, Ni 2+ and Co 2+ ions form impurity phases after complete occupying of the octahedral M5 site. The incorporation of these ions into the β-TCP crystal structure delays the phase transition to the α-TCP phase and stabilizes the structure as the temperature increases. Biocompatibility tests conducted on adipose tissue-derived mesenchymal stem cells (aMSC) using the (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) (MTT) assay showed that all prepared samples did not exhibit cytotoxic effects. Furthermore, there was no inhibition of cell differentiation into the osteogenic lineage. Antibacterial properties were studied on the C. albicans fungus and on E. coli , E. faecalis , S. aureus, and P. aeruginosa bacteria strains. The Ni- and Co-doped β-TCP series exhibited varying degrees of bacterial growth inhibition depending on the doping ion concentration and the specific bacteria strain or fungus. The combination of antibacterial activity and cell-friendly properties makes these phosphates promising candidates for anti-infection bone substitute materials.

A new series of Sr-based phosphates, Sr 9- x Mn x Eu(PO 4 ) 7 , were synthesized using the high-temperature solid-state method in air. It was found that these compounds have the same structure as strontiowhitlockite, which is a β-Ca 3 (PO 4 ) 2 (or β-TCP) structure. The concentration of Mn 2+ ions required to form a pure strontiowhitlockite phase was determined. An unusual partial reduction of Eu 3+ to Eu 2+ in air was observed and confirmed by photoluminescence (PL) and electron spin resonance (ESR) spectra measurements. The PL spectra recorded under 370 nm excitation showed transitions of both 4 f 5 d -4 f Eu 2+ and 4 f -4 f Eu 3+ . The total integral intensity of the PL spectra, monitored at 395 nm, decreased with increasing Mn 2+ concentration due to quenching effect of Eu 3+ by the Mn 2+ levels. The temperature dependence of Eu 2+ photoluminescence in a Sr 9- x Mn x Eu(PO 4 ) 7 host was investigated. The conditions for the reduction of Eu 3+ to Eu 2+ in air were discussed.

VO and VO 2 vanadyl groups with short (typically 1.57-1.68 Å), essentially covalent, V-O bonds are common for V 4+ -bearing oxysalts with [5]- and [6]-coordinated vanadium. There is a clear negative correlation between vanadyl bond lengths and wavenumbers of the bands of V-O stretching vibrations in infrared spectra (in the range 1000-880 cm -1 ). Optical, structural and chemical data for vanadyl minerals are used to calculate Gladstone-Dale compatibility coefficients. Gladstone-Dale compatibility indices of minerals containing vanadyl bonds are compared with total electronic polarizabilities of V 4+ . Unlike compounds of [5]-coordinated Ti 4+ , for most minerals with V 4+ =O (vanadyl) bonds there is good agreement between measured refractive indices and those calculated based on the polarizability concept.

The study of azoproite by Biryukov et al. [Acta Cryst. (2022), B78, 809-816) continues the systematic and complex investigation of the crystal structures, temperature behavior and magnetic properties of natural oxoborates.

Compounds with the general formula Ln 3+ (SeO 3 )(HSeO 3 )·2H 2 O, where Ln = Sm 3+ , Tb 3+ , Nd 3+ and Lu 3+ , are characterized by orthorhombic symmetry with space group P2 1 2 1 2 1 and unit-cell parameters in the ranges a ∼ 6.473-6.999, b ∼ 6.845-7.101, c ∼ 16.242-16.426 Å. Light-purple irregularly shaped crystals of a new monoclinic polytype of neodymium selenite Nd(SeO 3 )(HSeO 3 )·2H 2 O have been obtained during a mild-condition hydrothermal synthesis. The monoclinic unit-cell parameters are: a = 7.0815 (2), b = 6.6996 (2), c = 16.7734 (5) Å, β = 101.256 (1)°, V = 780.48 (6) Å 3 ; space group P2 1 /c. The crystal structures of Nd(SeO 3 )(HSeO 3 )·2H 2 O polymorphs show order-disorder (OD) character and can be described using the same OD groupoid family, more precisely a family of OD structures built up from two kinds of non-polar layers (category IV). The first monoclinic maximum degree order (MDO) structure (MDO1-polytype) with space group P2 1 /c can be obtained when the inversion centre is active in the L 2n -type layers, while the second MDO structure (MDO2-polytype) is orthorhombic with space group P2 1 2 1 2 1 and can be obtained when the [2 1 --] operation is active in the L 2n -type layers. The structural complexity parameters and DFT calculations of both polytypes show that the polytype structures are extremely close energy-wise and almost equally viable from the point of total energy of the structure.

Most known compounds with five-coordinated Ti 4+ are natural and synthetic titanosilicates. The crystal structure of natural fresnoite, Ba 2 TiSi 2 O 8 [tetragonal, space group P4bm, a = 8.510 (1) Å, c = 5.197 (1) Å, V = 376.4 (1) Å 3 , Z = 2], has been refined to R = 0.011 on the basis of 807 unique single-crystal reflections with I > 2σ(I). Titanium has fivefold coordination with one short (`titanyl') bond of 1.692 (5) Å. Bonds in the TiO 5 polyhedron are discussed in comparison to analogous coordination polyhedra in other minerals and compounds. A review of all known compounds with Ti 4+ O 5 polyhedra shows that most of them are titanosilicates in which titanium forms a short Ti-O bond (∼1.61 to ∼1.77 Å). Poor Gladstone-Dale compatibility between chemical composition, optical characteristics and density of these compounds is explained by the anomalous contribution of [5] Ti 4+ to the optical properties as shown by calculations based on the relationship between electronic polarizabilities and refractive indices. An improved Gladstone-Dale coefficient of 0.29 is suggested for TiO 2 with [5] Ti 4+ . A negative correlation between `titanyl' bond lengths and wavenumbers of the bands of Ti-O stretching vibrations (in the range of 890-830 cm -1 ) in infrared and Raman spectra is observed.

The identification of the framework type in multilayer cancrinite- and sodalite-group minerals and synthetic compounds is predominantly based on the unit-cell dimensions determined from powder or single-crystal X-ray diffraction data, by analogy with previously characterized samples with known crystal structures. However, topological type of the framework cannot be reliably determined in this way because of the different possible ABC staking sequences and different sets of cages with the same number of layers in the repeat unit. To solve this problem, additional criteria are required. The use of infrared (IR) spectroscopy makes it possible to distinguish topologically different types with the same unit-cell parameters. The most important diagnostic range in the IR spectrum (the "finger-print region", from 510 to 760 cm -1 ) corresponds to the O-T-O bending vibrations (T = Si, Al). The spectral bands at 705 ± 8, 528 ± 5, 547 ± 4, and 555 ± 3 cm -1 indicate the presence of the sodalite, Losod, liottite, and giuseppettite cages, respectively. The band at 528 ± 5 cm -1 shifts towards ∼518 cm -1 in the case when Losod cage hosts carbonate group. The IR spectrum in the "finger-print region" can be also used to identify a mineral species belonging to two-layer or three-layer minerals with different extra-framework compositions. The wavenumber of the antisymmetric stretching mode of the 12 CO 2 molecule, which is a common admixed extra-framework constituent in minerals belonging to the cancrinite and sodalite groups, depends on the kind of the host cage or channel: 2340-2343 cm -1 for the sodalite cage, 2338 cm -1 for the Losod cage, and 2351-2353 cm -1 for the liottite cage and wide channel in the cancrinite-type framework., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Using glass crystallization and solid-state techniques, we were able to complete the family of salt-inclusion silver halide borates, Ag 4 B 7 O 12 X, by the X = Cl and I members. The new compounds are characterized by differential scanning calorimetry, single-crystal and high-temperature powder X-ray diffraction, optical spectroscopy, and density functional theory calculations. In all structures, the silver atoms exhibit strong anharmonicity of thermal vibrations, which could be modeled using Gram-Charlier expansion, and its asymmetry was characterized by the skewness vector. The topology of the silver halide and borate sublattices has been analyzed separately for the first time. Along the I → Br → Cl series, we observe a decrease of the melting point and configuration entropy and an increase of thermal expansion and its anisotropy and thermal vibration anharmonicity, which indicates decreasing stability.

Topological analysis of the heteropolyhedral MT framework (where M and T are octahedral and tetrahedral cations, respectively) in the eudialyte-type structure and its derivatives was performed based on a natural tiling analysis of the 3D cation. To analyze the migration paths of sodium cations in these structures, the Voronoi method was used. The parental eudialyte-type MT framework is formed by isolated ZO 6 octahedra, six-membered [M(1) 6 O 24 ] rings of edge-sharing M(1)O 6 octahedra, and two kinds of rings of tetrahedra, [Si 3 O 9 ] and [Si 9 O 27 ]. Different occupancies of M(2), M(3) and M(4) sites with variable coordination numbers by the additional Q, T* and M* cations, respectively, result in 12 different types of the MT framework. Based on the results of natural tilings calculations as well as theoretical analysis of migration paths, it is found that Na + ions can migrate through six- and seven-membered rings, while all other rings are too small for the migration. In eight types of MT frameworks, Na + -ion migration and diffusion is possible at ambient temperature and pressure, while in four other types cages are connected by narrow windows and, as a result, the Na + diffusion in them is complicated at ambient conditions because of the window diameter, but may be possible either at higher temperatures or under mild geological conditions for long periods of time.

A series of solid-solution phosphate germanates Ca 8+0.5 x ZnEu(PO 4 ) 7- x (GeO 4 ) x ( x = 0, 0.2, 0, 4, 0.6, 0.8, 1) with the β-Ca 3 (PO 4 ) 2 -type structure were synthesized by solid-state reactions. The limit of existence of a single-phase solid solution was determined by X-ray diffraction patterns and it was found at x = 0.8. The heterovalent tetrahedral [PO 4 ] 3- → [GeO 4 ] 4- substitution requires a charge compensation according to the scheme: [PO 4 ] 3- + ½ □ → [GeO 4 ] 4- + ½ Ca 2+ . The additional amount of Ca 2+ ions in the crystal structure was detected at the M4 site during Rietveld refinement. It was shown that in β-Ca 3 (PO 4 ) 2 -type compounds, charge balancing is not provided by the randomly distributed oxygen vacancies but only by the partial occupancy of the M4 site. The presence of Ca 2+ at the M4 site leads to a polar structure with the space group R 3 c which was confirmed by an SHG test for all single-phase samples. It was shown that the Ge 4+ ions preferably occupy the T3 site in the structure, which is connected through common oxygen with the cationic M1-M5 sites. The analysis of the similarity of the previously reported Ca 9 La(GeO 4 ) 0.75 (PO 4 ) 6 compound reveals an unexpectedly high value. The same structural similarity evaluation of the studied compound Ca 8.1 EuZn(PO 4 ) 6.8 (GeO 4 ) 0.2 in the present work with the initial model gives a very small value, which indicates a good match between the initial and under-consideration structures. The luminescence properties of Eu 3+ were investigated from the point of view of crystal structures and anionic substitutions. The integral intensity increased linearly with the [PO 4 ] 3- → [GeO 4 ] 4- substitution. It can be concluded that the anionic substitution on Ge 4+ can improve the luminescence characteristics. The present study includes new data on the anionic substitution based on accurate crystal structure refinement.

Specific features of the crystal chemistry of lamprophyllite-group minerals (LGMs) are discussed using the available literature data and the results of the single-crystal X-ray diffraction and a Raman spectroscopic studies of several samples taken from the Murun alkaline complex (Russia), and Rocky Boy and Gordon Butte pegmatites (USA) presented here. The studied samples are unique in their chemical features and the distribution of cations over structural sites. In particular, the sample from the Gordon Butte pegmatite is a member of the barytolamprophyllite-emmerichite solid solution series, whereas the samples from the Murun alkaline complex and from the Rocky Boy pegmatite are intermediate members of the solid solution series formed by lamprophyllite and a hypothetical Sr analogue of emmerichite. The predominance of O 2- over OH - and F - at the X site is a specific feature of sample Cha-192 from the Murun alkaline complex. New data on the Raman spectra of LGMs obtained in this work show that the wavenumbers of the O-H stretching vibrations depend on the occupancies of the M2 and M3 sites coordinating with (OH) - groups. Cations other than Na + and Ti 4+ (mainly, Mg and Fe 3+ ) can play a significant role in the coordination of the X site occupied by (OH) - . Data on polarized Raman spectra of an oriented sample indicate that the OH groups having different local coordinations have similar orientations with respect to the crystal. The calculated measures of similarity (Δ) for lamprophyllite and ericssonite are identical (0.157 and 0.077 for the 2M- and 2O-polytypes, respectively), which indicates that these minerals are crystal-chemically isotypic and probably should be considered within the same mineral group by analogy to the other mineralogical groups which combine isotypic minerals.

The series of β-Ca 3 (PO 4 ) 2 -type phosphors Ca 9.5-1.5 x MgEu x (PO 4 ) 7 were synthesized by a solid-state route. Observation of the proper Eu 3+ ion distribution in the Ca 9.5 Mg(PO 4 ) 7 host matrix was made by a direct method using 151 Eu Mössbauer spectroscopy in combination with X-ray analysis and dielectric and luminescent spectroscopy. The photoluminescence properties were studied in detail. The samples exhibit an exceptionally narrow-band red emission according to the dominant 5 D 0 → 7 F 2 transition and fulfill the industrial requirements for high-energy-efficiency red phosphors. The contribution of Eu 3+ ions in different crystal sites to the luminescent properties is discussed in detail. The difference of the excitation of Eu 3+ in the M1 and M2 sites was revealed by photoluminescence excitation spectra in accordance with structure refinement. The temperature dependence of the luminescence intensity was studied. Different tendencies in the thermal behavior of emission lines allow one to consider the studied compounds as phosphors suitable for luminescence thermometry. The measured quantum yield for Ca 9.5-1.5 x MgEu x (PO 4 ) 7 shows excellent results and reaches 63%.

Two uranyl vanadate heteropolyoxometalates ( h -POMs) have been synthesized by ionothermal methods using the ionic liquid 1-ethyl-3-methylimidazolium diethyl phosphate (EMIm-Et 2 PO 4 ). The hybrid actinide-transition metal shell structures have cores of (UO 2 ) 8 (V 6 O 22 ) and (UO 2 ) 6 (V 3 O 12 ), which we designate as {U 8 V 6 } and {U 6 V 3 } , respectively. The diethyl phosphate anions of the ionic liquids in some cases terminate the core structures to form actinyl oxide clusters, and in other cases the diethyl phosphate oxyanions link these cluster cores into extended structures. Three compounds exist for the {U 8 V 6 } cluster core: {U 8 V 6 }-monomer , {U 8 V 6 }-dimer , and {U 8 V 6 }-chain . Tungsten atoms can partially substitute for vanadium in the {U 6 V 3 } cluster, which results in a chain-based structure designated as {U 6 V 3 }-W . Each of these compounds contains charge-balancing EMIm cations from the ionic liquid. These compounds were characterized crystallographically, spectroscopically, and by mass spectrometry.

Two uranium(IV) sulfate framework compounds were crystallized at room temperature from aqueous solutions containing uranyl ions by photochemical reduction in the presence of 2-propanol. U 3 H 2 (SO 4 ) 7 (H 2 O) 5 ·3H 2 O ( 1 ) crystallizes in space group P 6 5 with a = 9.3052(17) Å, c = 53.515(10) Å, V = 4012.9(13) Å 3 , and Z = 6, and U 3 (UO 2 ) 0.2 (SO 4 ) 6 (OH) 0.4 ·2.3H 2 O ( 2 ) is tetragonal, with space group P 4 2 / nmc , a = 25.624(3) Å, c = 8.9435(10) Å, V = 5872.2(11) Å 3 , and Z = 8. The structures of 1 and 2 are the most complex among uranium(IV) sulfates.

Single crystals of Rb 2 CaCu 6 (PO 4 ) 4 O 2 were synthesized by a hydrothermal method in the multicomponent system CuCl 2 -Ca(OH) 2 -RbCl-B 2 O 3 -Rb 3 PO 4 . The synthesis was carried out in the temperature range from 690 to 700 K and at the general pressure of 480-500 atm [1 atm = 101.325 kPa] from the mixture in the molar ratio 2CuO:CaO:Rb 2 O:B 2 O 3 :P 2 O 5 . The crystals studied by single-crystal X-ray analysis were found to be monoclinic, space group C2, a = 16.8913 (4), b = 5.6406 (1), c = 8.3591 (3) Å, β = 93.919 (3)°, V = 794.57 (4) Å 3 . The crystal structure of Rb 2 CaCu 6 (PO 4 ) 4 O 2 is similar to that of shchurovskyite and dmisokolovite and is based upon a heteropolyhedral open framework formed by polar layers of copper polyhedra linked via isolated PO 4 tetrahedra. The presence of well-isolated 2D heteropolyhedral layers in the title compound suggests low-dimensional magnetic behavior which is masked, however, by the fierce competition between multiple ferromagnetic and antiferromagnetic exchange interactions. At T C = 25 K, Rb 2 CaCu 6 (PO 4 ) 4 O 2 reaches a magnetically ordered state with large residual magnetization.

Solid UO 2 dissolution and uranium speciation in aqueous solutions that promote formation of uranyl peroxide macroanions was examined, with a focus on the role of alkali metals. UO 2 powders were dissolved in solutions containing XOH (X = Li, Na, K) and 30% H 2 O 2 . Inductively coupled plasma optical emission spectrometry (ICP-OES) measurements of solutions revealed linear trends of uranium versus alkali concentration in solutions resulting from oxidative dissolution of UO 2 , with X:U molar ratios of 1.0, showing that alkali availability determines the U concentrations in solution. The maximum U concentration in solution was 4.20 × 10 5 parts per million (ppm), which is comparable to concentrations attained by dissolving UO 2 in boiling nitric acid, and was achieved by lithium hydroxide promoted dissolution. Raman spectroscopy and electrospray ionization mass spectrometry (ESI-MS) of solutions indicate that dissolution is accompanied by the formation of various uranyl peroxide cluster species, the identity of which is alkali concentration dependent, revealing remarkably complex speciation at high concentrations of base.

The bismuth(III) oxophosphate Bi 3 (PO 4 )O 3 was obtained by hydrothermal synthesis. The unit cell has a = 5.6840(6) Å, b = 7.0334(7) Å, c = 9.1578(9) Å, α = 78.958(2)°, β = 77.858(2)°, γ = 68.992(2)°, V = 331.41(6) Å 3 , space group P1̅, and Z = 2. The crystal chemical formula that reflects the presence of oxo-centered tetrahedra and triangles is 2D [O III O IV 2 Bi 3 ](PO 4 ). The crystal structure contains [O 3 Bi 3 ] 3+ ∞∞ -heteropolyhedral corrugated layers parallel to (001), which alternate along [001] with isolated (PO 4 ) tetrahedra. The structural complexity parameters are v = 22 atoms, I G = 3.459 bits/atoms, and I G,total = 76.107 bits/unit cell, and thus Bi 3 (PO 4 )O 3 is the simplest pure bismuth(III) oxophosphate.

A hydroxyl-dominant analogue of gadolinite-(Y) (OH-Gad) has been discovered in the Heftetjern granitic pegmatite, southern Norway, in association with late-stage rare-earth-element containing minerals. The empirical formula, based on ten O atoms per formula unit, is (Y 1.285 Ca 0.55 Ce 0.07 La 0.04 Nd 0.01 ) Σ1.955 (Fe 2+ 0.57 □ 0.43 )Be 2.02 Si 1.995 O 8.48 (OH) 1.52 . The mineral is monoclinic, space group P2 1 /c, a = 4.7514 (10), b = 7.5719 (16), c = 9.9414 (2) Å, β = 90.015 (4)°, V = 357.663 (3) Å 3 and Z = 2. The density calculated using the empirical formula is 3.903 g cm -3 . The crystal structure was refined to R = 0.0217 for 776 reflections with I > 2σ(I). OH-Gad is isostructural with gadolinite-(Y) and it is characterized by the predominance of OH - over O 2- at the anionic Ø-site. The refined crystal-chemical formula is: A (Y 1.25 Ca 0.55 Ce 0.2 ) X (Fe 2+ 0.57 □ 0.43 ) Z Be 2 T Si 2 O 8 Ø [(OH) 0.86 O 0.59 (OH)* 0.55 ] (Z = 2). The possible orientation and local environment of the hydroxyl group were suggested based on bond-valence sum calculations and geometrical analysis of the crystal structure. The infrared spectrum confirms disordering of H atoms. OH-Gad seems to be a potentially new mineral, the first simultaneously hydroxyl- and iron-dominant member of the gadolinite subgroup. It is an OH-analogue of gadolinite-(Y) and an Fe 2+ -analogue of hingganite-(Y).

Vesuvianite containing 5.85 wt% TiO 2 from an Alpine-cleft-type assemblage outcropped near Alchuri, Shigar Valley, Northern Areas, Pakistan, has been investigated by means of electron microprobe analyses, gas-chromatographic analysis of H 2 O, X-ray powder diffraction, single-crystal X-ray structure refinement, 27 Al NMR, 57 Fe Mössbauer spectroscopy, IR spectroscopy and optical measurements. Tetragonal unit-cell parameters are: a = 15.5326 (2), c = 11.8040 (2) Å, space group P4/nnc. The structure was refined to final R 1 = 0.031, wR 2 = 0.057 for 11247 I > 2σ(I). A general crystal-chemical formula of studied sample can be written as follows (Z = 2): [8-9] (Ca 17.1 Na 0.9 ) [8] Ca 1.0 [5] (Fe 2+ 0.44 Fe 3+ 0.34 Mg 0.22 ) [6] (Al 3.59 Mg 0.41 ) [6] (Al 4.03 Ti 2.20 Fe 3+ 1.37 Fe 2+ 0.40 ) (Si 18 O 68 ) [(OH) 5.84 O 2.83 F 1.33 ]. The octahedral site Y2 is Al-dominant and does not contain transition elements. Another octahedral site Y3 is also Al-dominant and contains Fe 2+ , Fe 3+ and Ti. The site Y1 is split into Y1a and Y1b predominantly occupied by Fe 2+ and Fe 3+ , respectively. The role of the Y1 site in the diversity of vesuvianite-group minerals is discussed.

Calcinaksite, KNa[Ca(H2O)][Si4Ol0], a new natural member of the litidionite group, was found in a calcic xenolith from alkaline basalt of the Bellerberg volcano, Eastern Eifel region, Rhineland-Palatinate, Germany. The crystal structure has been studied based on single-crystal X-ray diffraction data. Triclinic unit-cell parameters are: a = 7.021 (2), b = 8.250 (3), c = 10.145 (2) Å, α = 102.23 (2), β = 100.34 (2), γ = 115.09 (3)°, space group P1. The structure model was determined by the `charge-flipping' method and refined to R = 0.0527 in anisotropic approximation using 3057 I > 3σ(I). Calcinaksite is a hydrous calcium-dominant litidionite-group mineral. The crystal structure of calcinaksite (like other litidionite-group minerals and related compounds) is based on a heteropolyhedral framework and is characterized by the presence of several types of channels. Calcium forms distorted CaO5Ø (Ø = H2O) octahedra while Na forms NaO5 square pyramids. Nine-coordinated K atoms are located in a channel extending along [010]. Water molecules occupy a channel running along the [100] direction and are characterized by a rather high equivalent isotropic displacement parameter of 0.053 (2) Å(2). In calcinaksite, there are three short distances between the water molecule and oxygen atoms, Ow...O3 [2.844 (5) Å], Ow...O9 [2.736 (4) Å] and Ow...Ow [2.843 (7) Å]. These distances correspond to three hydrogen bonds detected by IR data (the bands at 3340, 3170 and 3540 cm(-1)).