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The investigation of elemental composition, crystal structure and thermal behavior of vonsenite and hulsite from the Titovskoe boron deposit in Russia is reported. The structures of the borates are described in terms of cation-centered and oxocentred polyhedra. There are different sequences of double chains and layers consisting of oxocentred [OM4]n+tetrahedra and [OM5]n+tetragonal pyramids forming a framework. Elemental composition was determined by energy-dispersive X-ray spectroscopy (EDX). Oxidation states and coordination sites of iron and tin in the oxoborates are determined using Mössbauer spectroscopy and compared with EDX and X-ray diffraction data (XRD). According to results obtained from high-temperature Mössbauer spectroscopy, the Fe2+to Fe3+oxidation in vonsenite and hulsite occurs at approximately 500 and 600 K, respectively. According to the high-temperature XRD data, this process is accompanied by an assumed deformation of crystal structures and subsequent solid-phase decomposition to hematite and warwickite. It is seen as a monotonic decrease of volume thermal expansion coefficients with an increase in temperature. A partial magnetic ordering in hulsite is observed for the first time withTc≃ 383 K. Near this temperature, an unusual change of thermal expansion coefficients is revealed. Vonsenite starts to melt at 1571 K and hulsite melts at 1504 K. Eigenvalues of thermal expansion tensor are calculated for the oxoborates as well as anisotropy of the expansion is described in comparison with their crystal structures.

The new eudialyte-group mineral sergevanite, ideally Na15(Ca3Mn3)(Na2Fe)Zr3Si26O72(OH)3·H2O, was discovered in highly agpaitic foyaite from the Karnasurt Mountain, Lovozero alkaline massif, Kola Peninsula, Russia. The associated minerals are microcline, albite, nepheline, arfvedsonite, aegirine, lamprophyllite, fluorapatite, steenstrupine-(Ce), ilmenite, and sphalerite. Sergevanite forms yellow to orange-yellow anhedral grains up to 1.5 mm across and the outer zones of some grains of associated eudialyte. Its luster is vitreous, and the streak is white. No cleavage is observed. The Mohs' hardness is 5. Density measured by equilibration in heavy liquids is 2.90(1) g/cm3. Calculated density is equal to 2.906 g/cm3. Sergevanite is nonpleochroic, optically uniaxial, positive, with ω = 1.604(2) and ε = 1.607(2) (λ = 589 nm). The infrared spectrum is given. The chemical composition of sergevanite is (wt.%; electron microprobe, H2O determined by HCN analysis): Na2O 13.69, K2O 1.40, CaO 7.66, La2O3 0.90, Ce2O3 1.41, Pr2O3 0.33, Nd2O3 0.64, Sm2O3 0.14, MnO 4.15, FeO 1.34, TiO2 1.19, ZrO2 10.67, HfO2 0.29, Nb2O5 1.63, SiO2 49.61, SO3 0.77, Cl 0.23, H2O 4.22, –O=Cl –0.05, total 100.22. The empirical formula (based on 25.5 Si atoms pfu, in accordance with structural data) is H14.46Na13.64K0.92Ca4.22Ce0.27La0.17Nd0.12Pr0.06Sm0.02Mn1.81Fe2+0.58Ti0.46Zr2.67Hf0.04Nb0.38Si25.5S0.30Cl0.20O81.35. The crystal structure was determined using single-crystal X-ray diffraction data. The new mineral is trigonal, space group R3, with a = 14.2179(1) Å, c = 30.3492(3) Å, V = 5313.11(7) Å3, and Z = 3. In the structure of sergevanite, Ca and Mn are ordered in the six-membered ring of octahedra (at the sites M11 and M12), and Na dominates over Fe2+ at the M2 site. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 7.12 (70) (110), 5.711 (43) (202), 4.321 (72) (205), 3.806 (39) (033), 3.551 (39) (220, 027), 3.398 (39) (313), 2.978 (95) (), 2.855 (100) (404). Sergevanite is named after the Sergevan' River, which is near the discovery locality.

The article describes a history of studies of samarskite-(Y), YFe3+Nb2O8, from its discovery in the Ilmeny Mountains (South Urals) in 1839 to the moment of the solution of its crystal structure and refnement of chemical formula in 2019.

The new leucophosphite-group mineral ammoniotinsleyite is found in a guano deposit located on the Pabellón de Pica Mountain, Iquique Province, Tarapacá Region, Chile. Associated minerals are halite, gypsum, salammoniac and clay minerals. Ammoniotinsleyite occurs as pink to pale violet globular aggregates up to 3 mm across with individual single crystals ~10–15 μm. The mineral is brittle. Its Mohs hardness is 4. Dmeas. = 2.42(2) g cm–3 and Dcalc. = 2.451 g cm–3. The IR spectrum shows the presence of NH4+ and PO43– groups and H2O molecules. Ammoniotinsleyite is optically biaxial (+), α = 1.557(2), β = 1.559 (calc.), γ = 1.563(2) (λ = 589 nm); and 2Vmeas. = 75(10)°. The chemical composition (K, Mg, Ca, Al, Fe and P from electron-microprobe data; H, C and N measured by gas chromatography on products of ignition at 1200°C; wt.%) is: (NH4)2O 7.25, K2O 1.50, MgO 0.42, CaO 0.34, Al2O3 29.91, Fe2O3 2.36, P2O5 43.97, H2O 14.89, CO2 below detection limit, total 100.64. The empirical formula is [(NH4)0.88K0.10Ca0.02)]Σ1.00(Al1.86Fe3+0.09Mg0.03)Σ1.98(PO4)1.96(OH)1.05⋅2.11H2O. The idealised formula is (NH4)2Al2(PO4)2(OH)⋅2H2O. The crystal structure of ammoniotinsleyite was refined based on powder X-ray diffraction data, using the Rietveld method. The final agreement factors are: Rp = 0.0071, Rwp = 0.0093 and Robs = 0.0167. The new mineral is isostructural with tinsleyite, spheniscidite and leucophosphite. It is monoclinic, space group P21/n, a = 9.5871(1) Å, b = 9.6089(1) Å, c = 9.6467(2) Å, β = 103.4461(8)°, V = 864.31(2) Å3 and Z = 4. The strongest reflections of the powder X-ray diffraction pattern [d,Å(I,%)(hkl)] are: 7.56(23)($\bar{1}$01), 6.71(79)(011, 110), 5.947(100)(101, $\bar{1}$11), 4.676(36)(002, 200), 3.032(28)($\bar{1}$13, 031, 130), 2.958(25)($\bar{2}$22, 310, $\bar{1}$31) and 2.635(29)($\bar{2}$31).

The new alluaudite-group mineral badalovite was found in the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. It is associated with hematite, tenorite, cassiterite, johillerite, nickenichite, calciojohillerite, bradaczekite, metathénardite, aphthitalite, langbeinite, calciolangbeinite, sanidine, fluorophlogopite, fluoborite, tilasite, anhydrite, pseudobrookite, sylvite, halite, lammerite, urusovite, ericlaxmanite, arsmirandite, svabite, krasheninnikovite, euchlorine, wulffite and alumoklyuchevskite. Badalovite forms oblique-angled prismatic crystals up to 1 mm × 1 mm × 5 mm, typically combined in groups or crusts up to several hundred cm2 in area. The mineral is transparent, green, grey, yellow or colourless, with vitreous lustre. It is brittle, the Mohs hardness is 3½. Cleavage was not observed, the fracture is uneven. Dcalc is 4.02 g cm–3. Badalovite is optically biaxial (–), α = 1.753(3), β = 1.757(3), γ = 1.758(3) and 2Vmeas. = 50(10)°. Chemical composition (wt.%, electron-microprobe; holotype) is: Na2O 9.23, K2O 0.19, CaO 2.04, MgO 13.78, MnO 0.31, CuO 0.12, ZnO 0.24, Al2O3 0.06, Fe2O3 12.77, TiO2 0.01, SiO2 0.06, P2O5 0.33, V2O5 0.05, As2O5 61.51, SO3 0.02, total 100.72. The empirical formula based on 12 O apfu is Na1.67Ca0.20K0.02Mg1.92Zn0.02Mn0.02Cu0.01Fe3+0.90Al0.01(As3.01P0.03Si0.01)Σ3.05O12. The simplified formula is Na2Mg2Fe3+(AsO4)3. Badalovite is monoclinic, C2/c, a = 11.9034(3), b = 12.7832(2), c = 6.66340(16) Å, β = 112.523(3)°, V = 936.59(4) Å3 and Z = 4. The strongest reflections of the powder XRD pattern [d,Å(I)(hkl)] are: 6.41(38)(020), 5.505(20)(200), 3.577(23)($\bar{1}$31), 3.523(25)(310), 3.211(46)($\bar{1}$12), 2.911(28)($\bar{2}$22, $\bar{3}$12), 2.765(100)(240, 400) and 2.618(26)($\bar{1}$32). The crystal structure was solved from single-crystal XRD data with an R1 of = 2.49%. Badalovite is isostructural with other alluaudite-group minerals. Its simplified crystal chemical formula is A(1)NaA(1)’□A(2) □A(2)’NaM(1)MgM(2)(Mg0.5Fe3+0.5)2(AsO4)3 (□ – vacancy) and the end-member formula is NaNaMg(MgFe3+)(AsO4)3. The mineral is named in honour of the outstanding mineralogist and geochemist Stepan Tigranovich Badalov (1919–2014).

The paper opens a series devoted to the mineral diversity of the Mochalin Log rare earth element (REE) deposit, South Urals, Russia. There is a brief outline of the history of studies and geology of the deposit as well as the description of two new isostructural gatelite-group minerals, ferriperbøeite-(La) (CaLa3)(Fe3+Al2Fe2+)[Si2O7][SiO4]3O(OH)2 and perbøeite-(La) (CaLa3)(Al3Fe2+)[Si2O7][SiO4]3O(OH)2. Both minerals occur in polymineralic nodules and are associated with one another and allanite-(Ce), allanite-(La), bastnäsite-(Ce), bastnäsite-(La), ferriallanite-(Ce), ferriallanite-(La), ferriperbøeite-(Ce), perbøeite-(Ce), törnebohmite-(Ce) and törnebohmite-(La). The new minerals form isolated anhedral grains up to 0.3 mm [ferriperbøeite-(La)] and 0.5 mm [perbøeite-(La)] across and granular aggregates up to 1.5 mm × 0.5 mm [ferriperbøeite-(La)] and 3 mm × 1 mm [perbøeite-(La)]. Both minerals are brownish-black with vitreous lustre. Dcalc = 4.510 [ferriperbøeite-(La)] and 4.483 [perbøeite-(La)] g cm–3. They are optically biaxial (+); ferriperbøeite-(La): α = 1.788(5), β = 1.790(5), γ = 1.810(5) and 2Vmeas = 40(10)°; perbøeite-(La): α = 1.778(8), β = 1.783(8), γ = 1.805(8) and 2Vmeas = 40(10)°. Chemical data [wt.%, electron-microprobe; Fe3+:Fe2+ ratio from charge-balance requirements, H2O by stoichiometry; ferriperbøeite-(La)/perbøeite-(La)] are: CaO 4.91/4.81, ThO2 0.00/0.32, La2O3 23.75/22.16, Ce2O3 19.69/20.05, Pr2O3 0.85/1.09, Nd2O3 1.48/2.18, MgO 1.47/1.38, Al2O3 10.68/11.25, MnO 1.07/0.92, FeO 3.04/3.35, Fe2O3 5.31/3.78, TiO2 0.19/0.19, SiO2 27.47/27.35, F 0.11/0.23, H2O 1.61/1.54, –O = F –0.05/–0.10, total 101.58/100.50. The empirical formulae based on O20(OH,F)2 are for ferriperbøeite-(La): (Ca0.95La1.58Ce1.30Nd0.10Pr0.06)Σ3.99(Al2.27Fe3+0.72Fe2+0.46Mg0.40Mn0.16Ti0.03)Σ4.04Si4.96O20[(OH)1.94F0.06]; and for perbøeite-(La): (Ca0.94Th0.01La1.49Ce1.34Nd0.14Pr0.07)Σ3.99(Al2.42Fe3+0.52Fe2+0.51Mg0.38Mn0.14 Ti0.03)Σ4.00Si4.99O20[(OH)1.87F0.13]. Both minerals are monoclinic, P21/m; the unit-cell parameters [ferriperbøeite-(La)/perbøeite-(La)] are: a = 8.9458(2)/8.9652(4), b = 5.72971(13)/5.7306(2), c = 17.6192(3)/17.6770(9) Å, β = 115.9497(19)/116.053(6)°, V = 812.06(3)/815.88(6) Å3 and Z = 2/2. The crystal structures are solved on a single crystal and converged to R = 0.0355 [ferriperbøeite-(La)] and 0.0750 [perbøeite-(La)]. Ferriperbøeite-(La) and perbøeite-(La) are named as the La-analogues of ferriperbøeite-(Ce) and perbøeite-(Ce), respectively.

A new niobium-rich lomonosovite variety with a high degree of ordering of Ti and Nb atoms has been investigated by X-ray diffraction analysis and electron probe microanalysis. Its simplified formula is Na10Ti2(Nb,Fe,Ti)2(Si2O7)2(PO4)2O4. The triclinic unit-cell parameters are a = 5.411(1) A, b = 7.108(1) A, c = 14.477(2) A, α = 99.78(1)°, β = 96.59(1)°, γ = 90.26(1)°, V = 544.94(5) A3, Z = 1, sp. gr. P1. The crystal structure has been refined to the final reliability factor R = 6.3% within the anisotropic approximation of atomic displacements using 3674 reflections with F > 3σ(F). The problem of niobium distribution in minerals with structures of lomonosovite and related types is discussed.

—We overview recent data on the mineralogy of oxidizing-type fumaroles of the Tolbachik Volcano (Kamchatka, Russia), with the main focus on the chemical specifics of the minerals. The active fumarole fields of Tolbachik are the most prominent mineral-forming exhalative system of this type in the world. About 350 mineral species, including 123 minerals first discovered here, are reliably identified in the Tolbachik fumaroles. The species diversity and the specifics of this mineralization are due to the unique combination of the physicochemical conditions and mechanisms of its formation: high temperatures, atmospheric pressure, superhigh oxygen fugacity, gas transport of most of chemical elements, and direct deposition of many high-temperature minerals from volcanic gases with a specific geochemical composition, including strong enrichment in alkaline metals and chalcophile (“ore”) elements. Sublimate silicates and minerals of As, Cu, Zn, Mn, Ti, Sn, Sb, Se, Au, Ag, Cs, Tl, and F are briefly described in terms of mineral geochemistry.

The new mineral kainotropite Cu4Fe3+O2(V2O7)(VO4) was found in sublimates of fumaroles related to the Tolbachik volcano, Kamchatka, Russia. The holotype specimen originates from the Yadovitaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption; associated minerals are hematite, langbeinite, calciolangbeinite, tenorite, piypite, lyonsite, rutile, pseudobrookite, sanidine, and lammerite. In paleo-fumarolic deposits of Mountain 1004 kainotropite is associated with diopside and hematite. It forms prismatic crystals up to 0.2 × 0.2 × 0.5 mm3, isolated or combined in clusters up to 0.7 mm across. Kainotropite is iron-black to reddish-black, with semi-metallic luster. Dcalc is 4.10 g/cm3. In reflected light, kainotropite is grey, weakly anisotropic. The reflectance values [Rmax–Rmin,% (λ, nm)] are: 18.3–17.3 (470), 17.3–16.3 (546), 16.9–15.7 (589), 16.3–15.1 (650). The chemical composition of the holotype sample (wt.%, electron microprobe) is: CuO 46.69, Al2O3 1.40, Fe2O3 10.04, TiO2 0.32, V2O5 37.58, As2O5 2.55, MoO3 0.76, total 99.34. The empirical formula, based on 13 O apfu, is: Cu3.96Fe3+0.85Al0.19Ti0.03(V2.78As0.15Mo0.04)Σ2.97O13. Kainotropite is orthorhombic, Pnma, a = 14.139(2), b = 6.7102(7), c = 11.4177(15) Å, V = 1083.3(2) Å3, and Z = 4. The strongest reflections of the powder XRD pattern [d,Å(I)(hkl)] are: 8.89(100)(101), 5.728(33)(002), 3.698(35)(212), 3.357(52)(020,203), 3.034(77)(220), 2.968(60)(303), and 2.655(27)(321,204). The crystal structure was solved from single-crystal XRD data, R = 0.085. Kainotropite represents a novel structure type. Cu2+ polyhedra (distorted tetragonal pyramids and strongly distorted octahedra) and Fe3+ octahedra are connected via common edges to form zigzag ribbons. Adjacent ribbons are connected by both V2O7 and VO4 groups (isolated from each other) to form a heteropolyhedral pseudo-framework. The name kainotropite is derived from the Greek word καινóτρoπoς, unusual, in allusion to its uncommon (for natural vanadates) anionic composition: it is the first mineral containing both pyrovanadate (V2O7)4– and orthovanadate (VO4)3– anions.

An eudialyte-group representative containing S2– sulfide anion has been investigated by X-ray diffraction analysis, electron-probe microanalysis, and IR spectroscopy. The unit-cell parameters are found to be a = 14.2156(3) A, c = 30.405(1) A, and V = 5321.16(3) A3; sp. gr. R3m. The crystal structure is refined to the final reliability factor R = 3.9% in the anisotropic approximation of atomic displacements using 2158 reflections with F > 3σ(F). The idealized formula of the mineral (Z = 3) is [(Na,Н3О)14Sr]Ca6(Mn2Na)Zr3[Si26O72](OH)3S2– · 2H2O. The problems of mineral origin and presence of sulfide sulfur in the minerals with eudialyte-type structure are discussed.

Natroaphthitalite K(Na,K)2Na(SO4)2, a new aphthitalite-group mineral, was found in exhalations of the active Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka Peninsula, Russia. The associated minerals are anhydrite, langbeinite, hematite, tenorite, sanidine, johillerite, tilasite, and belomarinaite. Natroaphthitalite occurs as translucent yellow to colorless roundish single-crystal individuals up to 1 cm in diameter, sometimes combined in crusts up to 2 cm across, and as aqua-transparent colorless tabular to lamellar hexagonal crystals up to 2 mm across, sometimes skeletal, typically combined in parallel intergrowths or brush-like aggregates. Dcalc is 2.664 g/cm3. Natroaphthitalite is optically uniaxial (+), ω = 1.488(2), ε = 1.490(2). The chemical composition (wt.%, electron microprobe) is: Na2O 22.54, K2O 26.39, SO3 51.78, total 100.71. The empirical formula calculated based on 8 O apfu is K1.735Na2.252S2.002O8 (average of 15 spot analyses). The crystal structures of natroaphthitalite and the associated aphthitalite-group mineral belomarinaite, ideally KNaSO4, from the Arsenatnaya fumarole were solved using single-crystal X-ray diffraction and refined to R1 = 0.0283 and 0.0261, respectively. The unit-cell parameters, Z, and space groups are a = 5.6014(3), c = 7.1507(5) Å, V = 194.30(2) Å3, Z = 1, and for natroaphthitalite and a = 5.6088(3), c = 7.1858(4) Å, V = 195.77(1) Å3, Z = 2, and P3m1 for belomarinaite. The crystal chemical formulae of natroaphthitalite and belomarinaite (Z = 1) are XK1.00Y(Na1.28K0.72)Σ2.00MNa1.00(TSO4)2 and XK1.00Y1(Na0.96K0.04)Σ1.00Y2(K0.94Na0.06)Σ1.00MNa1.00(TSO4)2, respectively. Natroaphthitalite is isostructural with aphthitalite K3Na(SO4)2 = XKYK2MNa(TSO4)2 (both have centrosymmetric structures) with prevailing Na over K at the Y site of the crystal structure. Belomarinaite XKY2KY1NaMNa(TSO4)2 is the fully cation-ordered species, with acentric structure, in the series of natural aphthitalite-like K-Na sulfates.

The problem to be solved is whether Al is a necessary component of Fe-Mg chlorites. Very unusual Al-depleted and Fe-enriched trioctahedral chlorites with the empirical formulae Na0.05Ca0.05(Fe2+3.01Mg2.01Ti0.14Fe3+0.04)Σ6.00[(Si3.53Fe3+0.41Al0.06)Σ4.00O10](OH)8·nH2O (Sample 1) and Na0.05Ca0.01(Fe2+3.26Mg1.97Fe3+0.75Mn0.01Ti0.01)Σ6.00[(Si3.16Fe3+0.75Al0.09)Σ4.00O10](OH)8 (Sample 2) have been discovered in Al-depleted dolomite carbonatites of the Kovdor complex of ultramafic, alkaline rocks and carbonatites, Kola Peninsula, Russia. The presence of substantial amounts of Ti in Sample 1 is another unusual feature of this mineral. In both samples, chlorites are intimately intergrown with cronstedtite-1T which is an indication of a low stability of chlorite structure in the absence of aluminum in the tetrahedral sheet. The crystal structure of chlorite in Sample 1 was solved by the Rietveld method. The mineral is triclinic (IIb-4-module), space group C-$$ 1 $$, a = 5.4153(4), b = 9.3805(7), c = 14.5743(12) A, α = 90.137(5)°, β = 96.928(5)°, γ = 90.043(6)°, V = 734.95(10) A3, and Z = 2. A problem to be solved is how stable are Al-free chlorites belonging to the clinochlore–chamosite solid-solution series and whether their existence in natural mineral assemblages is possible. The results obtained indicate that even though Al-depleted chlorites belonging to the clinochlore–chamosite solid-solution series exist in Nature as metastable phases, these minerals are extremely rare and much less stable than Al-poor serpentines.

This is the initial paper in a pair of articles devoted to silicate minerals from fumaroles of the Tolbachik volcano (Kamchatka, Russia). These papers contain the first systematic data on silicate mineralization of fumarolic genesis. In this article nesosilicates (forsterite, andradite and titanite), cyclosilicate (a Cu,Zn-rich analogue of roedderite), inosilicates (enstatite, clinoenstatite, diopside, aegirine, aegirine-augite, esseneite, “Cu,Mg-pyroxene”, wollastonite, potassic-fluoro-magnesio-arfvedsonite, potassic-fluoro-richterite and litidionite) and phyllosilicates (fluorophlogopite, yanzhuminite, “fluoreastonite” and the Sn analogue of dalyite) are characterized with a focus on chemistry, crystal-chemical features and occurrence. Unusual As5+-rich varieties of forsterite, andradite, titanite, pyroxenes, amphiboles and mica are described. General data on silicate-bearing active fumaroles and the diversity and distribution of silicates in fumarole deposits are reported. Evidence for the fumarolic origin of silicate mineralization is discussed.

This second of two companion articles devoted to silicate mineralization in fumaroles of the Tolbachik volcano (Kamchatka, Russia) reports data on chemistry, crystal chemistry and occurrence of tectosilicates: sanidine, anorthoclase, ferrisanidine, albite, anorthite, barium feldspar, leucite, nepheline, kalsilite, sodalite and hauyne. Chemical and genetic features of fumarolic silicates are also summarized and discussed. These minerals are typically enriched with “ore” elements (As, Cu, Zn, Sn, Mo, W). Significant admixture of As5+ (up to 36 wt % As2O5 in sanidine) substituting Si is the most characteristic. Hauyne contains up to 4.2 wt % MoO3 and up to 1.7 wt % WO3. All studied silicates are hydrogen-free, including mica and amphiboles which are F-rich. Iron-bearing minerals contain only Fe3+ due to strongly oxidizing formation conditions. In Tolbachik fumaroles, silicates were formed in the temperature range 500–800 ∘C as a result of direct deposition from the gas phase (as volcanic sublimates) or gas–rock interactions. The zonation in distribution of major silicate minerals observed in a vertical section of the Arsenatnaya fumarole, from deep (the hottest) to upper parts is diopside + forsterite + enstatite + andradite → diopside → fluorophlogopite + diopside → sanidine + fluorophlogopite → sanidine. This is in agreement with volatilities of major species-defining metals in volcanic gases. From a crystal-chemical viewpoint, this series corresponds to the following sequence of crystallization of minerals with temperature decrease: nesosilicates → inosilicates → phyllosilicates → tectosilicates.

This paper describes specific features of isomorphism of unusual amphiboles containing up to 23 wt% ZnO and up to 1.3 wt% CuO from sulfide-free metasomatic rocks of the “Mixed Series” metamorphic complex, Pelagonian Massif, Republic of North Macedonia, in which chalcophile elements (Pb, Cu, Zn, Sb, As) occur in high concentrations in the form of oxides and oxysalts. The studied amphiboles belong to six mineral species: magnesio-riebeckite, ferri-winchite, F-dominant analogue of ferri-winchite (“ferri-fluoro-winchite”), ferri-barroisite, ferri-nyboite, and a zinc-rich amphibole related to clino-suenoite. The main substitution schemes are Zn → Mg and Na + Fe3+ → Ca + Mg. The amphibole related to clino-suenoite has been studied in the most detailed way. Its empirical formula is (Mg2.99Zn2.47Mn1.26Fe3+0.30Ca0.07)Σ7.09(Si7.89Fe3+0.06Al0.05O22)(OH)2, and it is the most Zn-rich amphibole among those that have ever been described in literary sources. This amphibole is characterized by single-crystal and powder X-ray diffraction, IR spectroscopic and optical data. The role of high barium activity in the formation of sulfide-free ores of chalcophile elements has been substantiated. A possible mechanism of sulfur immobilization can be described by the scheme S2− + 2O2 ↔ SO42−; SO42− + Ba2+ → BaSO4↓.

—Hydrotalcite supergroup minerals stichtite, pyroaurite, iowaite, and woodallite form a complex solid-solution system at the Kyzyl-Uyuk locality (Terekta Ridge, Gorny Altai, Russia). The diversity of these minerals is due to: (1) subdivision by anionic interlayer composition into carbonate (stichtite and pyroaurite) and chloride (iowaite and woodallite) species and (2) isomorphism of M3+ cations, mainly between Cr- (stichtite and woodallite) and Fe3+-dominant species (pyroaurite and iowaite), with a quantitative predominance of stichtite and iowaite. Most of the studied samples correspond to stichtite and woodallite with high Fe3+ contents or pyroaurite and iowaite with high Cr3+ contents. According to vibrational (IR and Raman) spectroscopy data, the interlayer Cl– is partially substituted by OH– rather than CO32- groups. We suppose that the presence/absence of a band in the region 1400–1350 cm–1 in the Raman spectra of stichtite can be explained by the local distortion of triangular CO3 groups. Stichtite and iowaite occur here in polytypic modifications 3R and 2H that are the most widespread for the hydrotalcite supergroup iowaite and stichtite is 2:1. For both minerals, the polytype 3R strongly dominates over 2H. The lowest 3R/2H ratio determined for the Terekta iowaite and stichtite is 2:1. The Altai stichtite is close in 3R/2H to the stichtite from Tasmania (Australia) and differs significantly from that in Transvaal samples (South Africa).

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

The new mineral yarzhemskiite, K[B5O7(OH)2]⋅H2O, was found in a halite–sylvite evaporite rock at the Chelkar salt dome, Western Kazakhstan Region, Kazakhstan. It is also associated with carnallite, polyhalite, gypsum, strontioginorite, satimolite and quartz. Yarzhemskiite occurs as separate thick tabular, short prismatic or equant crystals up to 0.5 mm × 0.7 mm × 1 mm and grains having irregular outlines up to 1 mm × 1.5 mm × 2 mm. The mineral is transparent, colourless, with vitreous lustre. It is brittle, the Mohs’ hardness is ca 2½. Cleavage is perfect on {100}. Dmeas is 2.13(1) and Dcalc is 2.112 g cm–3. Yarzhemskiite is optically biaxial (+), α = 1.484(2), β = 1.508(2), γ = 1.546(2), 2Vmeas = 75(10)° and 2Vcalc = 80°. Chemical composition (wt.%, electron microprobe, H2O was calculated by stoichiometry) is: Na2O 0.01, K2O 17.84, CaO 0.07, B2O3 67.21, H2Ocalc 13.91, total 99.04. The empirical formula based on 10 O atoms per formula unit is K0.98B5.005O7(OH)2⋅H2O. Yarzhemskiite is monoclinic, P21/c, a = 9.47340(18), b = 7.52030(16), c = 11.4205(2) Å, β = 97.3002(17)°, V = 807.03(3) Å3 and Z = 4. The strongest reflections of the powder XRD pattern [d,Å(I,%)(hkl)] are: 9.39(86)(100), 4.696(41)(200), 3.296(18)($\bar{1}$13), 3.130(19)(022, 300), 2.935(42)(220), 2.898(100)($\bar{3}$02, $\bar{2}$21, 310), 2.832(56)(004) and 1.867(18)($\bar{2}$25). The crystal structure was solved based on single-crystal X-ray diffraction data, R1 = 3.36%. The structure contains infinite chains built by boron-centred polyhedra. The basic structural unit of the chain is a double ring B5O7(OH)2 consisting of one BO4 tetrahedron and four BO3 triangles. K+ cations centre ten-fold polyhedra which form, together with the borate chains [B5O7(OH)2]–∝, layers linked with each other only via H bonds. The mineral is named in honour of the Russian geologist, petrologist and mineralogist Yakov Yakovlevich Yarzhemskii (1901–?), a specialist in petrology of evaporite rocks and mineralogy and genesis of boron deposits related to evaporites.

Dalnegorskite, a new pyroxenoid with the crystal chemical formula Ca2Ca2MnCa(Si3O9)2 and simplified formula Ca5Mn(Si3O9)2, is a rock-forming mineral in the B-bearing calcic skarns in the Dalnegorsk borosilicate deposit (Dalnegorsk, Primorsky Krai, Russia). It belongs to the bustamite structural type and forms a continuous solid-solution series with isostructural ferrobustamite Ca2Ca2FeCa[Si3O9]2. These pyroxenoids form beige, pinkish white and milky white radiated aggregates typically consisting of split thin acicular to fiber-like individuals and are associated with hedenbergite, datolite, andradite, galena, sphalerite, and pyrrhotite. Dmeas. = 3.02(2), Dcalc. = 3.035 g cm–3. Dalnegorskite is biaxial negative, α = 1.640 (3), β = 1.647 (3), γ = 1.650 (3)°, 2Vmeas. = 75(10)°. The average chemical composition of the holotype (electron microprobe data) is: 0.23 MgO, 40.02 CaO, 5.02 MnO, 3.64 FeO, 50.65 SiO2, total 99.56 wt %. The empirical formula calculated for 18 O atoms is Ca5.03Mn0.51Fe0.36Mg0.04Si6.01O18. The crystal structure of the new mineral was obtained from X-ray diffraction data using the Rietveld method, Rp= 0.0345, Rwp = 0.0444, R1 = 0.0790, and wR2 = 0.0802. Dalnegorskite is triclinic, P-1, a = 7.2588(11), b = 7.8574(15), c = 7.8765(6) A, α = 88.550(15), β = 62.582(15), γ = 76.621(6)°, V = 386.23(11) A3, and Z = 1. Dalnegorskite is distinct from the related mineral wollastonite in the infrared spectrum. The wave numbers of the maxima of strong bands in the Si–O stretching vibration region in the IR spectrum of dalnegorskite are (cm–1): 905, 937, 1025, and 1070. The holotypic specimen of dalnegorskite is kept in the collection of the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow, Russia (no. 96201).

Thermal behavior of catapleiite, ideally Na2ZrSi3O9 ⋅ 2H2O, has been investigated with the X-ray diffraction, electroconductivity measurements using impedance spectroscopy, dynamic scanning calorimetry, thermal gravimetry, and infrared spectroscopy. The high-temperature transformation product of catapleiite obtained after annealing of catapleiite at 1000°C has been studied. This is a new microporous zirconosilicate, ideally Na6Zr3[Si9O27], representing a new structural type. It is hexagonal, P63/mcm, a = 11.5901(9), c = 9.9546(9) A, V = 1158.05(16) A3. Its crystal structure model has been obtained using single-crystal X-ray diffraction data and refined by the Rietveld method on the basis of the powder X-ray diffraction data (R = 3.87%). The structure is based on the heteropolyhedral framework, which substantially differs from that of catapleiite and is built by nine-member rings Si9O27 formed by SiO4 tetrahedra linked with isolated ZrO6 octahedra. Extraframework Na cations are located in broad channels of the framework and between the tetrahedral Si9O27 rings.

The new beudantite-group mineral oberwolfachite, ideally SrFe3+3(AsO4)(SO4)(OH)6, was discovered in two localities: Clara mine, Oberwolfach, Schwarzwald, Baden-Württemberg, Germany (holotype) and Monterniers mine, Lantignié, Rhône, Auvergne-Rhône-Alpes, France (cotype). The associated minerals are quartz, baryte, hematite, illite, goethite, beudantite and dussertite (Clara) and arsenogoyazite, jarosite, graulichite-(Ce), goethite and hematite (Monterniers). Oberwolfachite forms yellow to brown platy crystals up to 1 mm across or thick outer zones of mixed (oberwolfachite–beudantite) crystals up to 3 mm across. The lustre is adamantine and the streak is yellow. A distinct cleavage on {0001} is observed. Calculated density is 3.874 g⋅cm–3. The infrared spectra are given. The chemical composition of the holotype/cotype samples are (wt.%, b.d.l. = below detection limit): K2O 1.25/1.86, SrO 6.41/11.15, BaO 8.13/0.45, PbO 2.18/b.d.l., Al2O3 0.16/0.23, Fe2O3 38.99/39.98, La2O3 1.68/not determined, Ce2O3 1.28/2.06, P2O5 0.12/b.d.l., As2O5 17.55/16.55, SO3 12.86/14.99, H2O (calculated) 8.72/9.05, total 99.33/96.62. The empirical formula of the holotype sample is (Sr0.38Ba0.33K0.16Pb0.06La0.06Ce0.05)Σ1.04(Fe3+3.03Al0.02)Σ3.05[(SO4)1.00(AsO4)0.95(PO4)0.01](O6.16H6.00). The crystal structures of both samples were determined using single-crystal X-ray diffraction data and refined to R = 3.13% (holotype, 293 K) and 2.65% (cotype, 170 K). Oberwolfachite is trigonal, R${\bar 3}$m, with a = 7.3270(3) Å, c = 17.0931(9) Å and V = 794.70(8) Å3 (holotype), and a = 7.298(2) Å, c = 16.908(3) Å and V = 779.8(4) Å3 (cotype); Z = 3. The strongest lines of the powder X-ray diffraction pattern of holotype [d, Å (I, %)(hkl)] are: 5.95 (56)(101), 3.664 (37)(110), 3.117 (16)(021), 3.082 (100)(113), 2.548 (15)(024), 2.280 (22)(107), 1.983 (26)(303) and 1.832 (19)(220).

The isomorphism of S-bearing feldspathoids belonging to the cancrinite, sodalite, tugtupite, vladimirivanovite, bystrite, marinellite and scapolite structure types has been investigated using a multimethodical approach based on infrared, Raman and electron spin resonance (ESR), as well as ultraviolet, visible and near infrared (UV–Vis–near IR) absorption spectroscopy methods and involving chemical and X-ray diffraction data. Sapozhnikovite Na8(Al6Si6O24)(HS)2 and sulfite and thiosulfate analogues of cancrinite are synthesized hydrothermally and characterized by means of electron microprobe analyses, powder X-ray diffraction and Raman spectroscopy. The possibility of the incorporation of significant amounts of SO42−, S4 and SO32− in the crystal structures of cancrisilite, sulfhydrylbystrite and marinellite, respectively, has been established for the first time. Thermal conversions of S-bearing groups in the synthetic sulfite cancrinite and sapozhnikovite analogues as well as natural vladinirivanovite and S4-bearing haüyne under oxidizing and reducing conditions have been studied using the multimethodical approach. The SO42− and S2− anions and the S3•– radical anion are the most stable S-bearing species under high-temperature conditions (in the range of 700–800 °C); their ratio in the heated samples is determined by the redox conditions and charge-balance requirement. The HS− and S52− anions are stable only under highly reducing conditions.

Fluorapophyllite-(Cs) (IMA 2018-108a), ideally CsCa4(Si8O20)F(H2O)8, is an apophyllite-group mineral from the moraine of the Darai-Pioz glacier, Tien-Shan, Northern Tajikistan. Associated minerals are quartz, pectolite, baratovite, aegirine, leucosphenite, pyrochlore, neptunite, fluorapophyllite-(K), and reedmergnerite. Fluorapophyllite-(Cs) is a hydrothermal mineral. It is colorless and has a vitreous luster and a white streak. Cleavage is perfect; it is brittle and has a stepped fracture. Mohs hardness is 4.5–5. Dmeas. = 2.54(2) g/cm3, Dcalc. = 2.513 g/cm3. Fluorapophyllite-(Cs) is unixial (+) with refractive indices (λ = 589 nm) ω = 1.540(2), ε = 1.544(2). It is non-pleochroic. Chemical analysis by electron microprobe gave SiO2 48.78, Al2O3 0.05, CaO 22.69, Cs2O 10.71, K2O 1.13, Na2O 0.04, F 1.86, H2Ocalc. 14.61, –O=F2 –0.78, sum 99.09 wt.%; H2O was calculated from crystal-structure analysis. The empirical formula based on 29 (O + F) apfu, H2O = 8 pfu, is (Cs0.75K0.24)Σ0.99(Ca3.99Na0.01)Σ4(Si8.01Al0.01)Σ8.02O20.03F0.97(H2O)8, Z = 2. The simplified formula is (Cs,K)(Ca,Na)4(Si,Al)8O20F(H2O)8. Fluorapophyllite-(Cs) is tetragonal, space group P4/mnc, a 9.060(6), c 15.741(11) Å, V 1292.10(19) Å3. The crystal structure has been refined to R1 = 4.31% based on 498 unique (Fo > 4σF) reflections. In the crystal structure of fluorapophyllite-(Cs), there is one [4]T site occupied solely by Si, = 1.615 Å. SiO4 tetrahedra link to form a (Si8O20)8– sheet perpendicular to [001]. Between the Si–O sheets, there are two cation sites: A and B. The A site is coordinated by eight H2O groups [O(4) site], A–O(4) = 3.152(4) Å; the A site contains Cs0.75K0.24□0.01, ideally Cs apfu. The Cs–O bond length of 3.152 Å is definitely larger than the K–O bond length of 2.966–2.971 Å in fluorapophyllite-(K), KCa4(Si8O20)F(H2O)8. The [7]B site contains Ca3.99Na0.01, ideally Ca4apfu; = 2.417 Å (φ = O, F, H2O). The Si–O sheets connect via A and B polyhedra and hydrogen bonding; two H atoms have been included in the refinement. Fluorapophyllite-(Cs) is isostructural with fluorapophyllite-(K). Fluorapophyllite-(Cs) is a Cs-analogue of fluorapophyllite-(K).

A new mineral, metathénardite, ideally Na2SO4, the high-temperature hexagonal dimorph of thénardite, a natural analogue of the synthetic phase Na2SO4(I), was found in the sublimates of active fumaroles at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure eruption, Tolbachik volcano, Kamchatka, Russia. The holotype originates from the Glavnaya Tenoritovaya fumarole in which metathénardite is associated with hematite, tenorite, fluorophlogopite, sanidine, anhydrite, krasheninnikovite, vanthoffite, glauberite, johillerite, and lammerite. The cotypes 1 and 2 are from the Arsenarnaya (with hematite, tenorite, fluorophlogopite, sanidine, euchlorine, wulffite, anhydrite, fluoborite, johillerite, nickenichite, calciojohillerite, badalovite, tilasite, cassiterite, and pseudobrookite) and the Yadovitaya (with tenorite, euchlorine, fedotovite, dolerophanite, langbeinite, krasheninnikovite, anhydrite, and hematite) fumaroles, respectively. All specimens with metathénardite were collected from areas with temperatures of 350–400 °C. Metathénardite forms hexagonal tabular, lamellar, or dipyramidal crystals (forms: {001}, {100}, {102}, and {201}) up to 3 mm combined in crusts up to several hundred cm2 in area. The mineral is transparent to semitransparent, colorless, white, light-blue, greenish, yellowish, grayish or brownish, with vitreous luster. Dmeas. = 2.72(1), Dcalc. = 2.717 g/cm3. Metathénardite is optically uniaxial (–), ω = 1.489(2), ε = 1.486(2). The empirical formulae are (Na1.92K0.05Ca0.02Zn0.01)[S0.99O4] (holotype), (Na1.54K0.22Ca0.09Cu0.01Mg0.01)[S1.00O4] (cotype 1), and Na1.65K0.11Ca0.05Cu0.04Mg0.01)[S1.01O4] (cotype 2). Admixed K and bivalent cations probably stabilize the hexagonal aphthitalite-like structure of metathénardite at room temperature. The crystal structure was solved using single crystals of all three samples, R1 = 0.0852, 0.0452, and 0.0449 for holotype and cotypes 1 and 2, respectively. The space group is P63/mmc, and the unit-cell parameters of the holotype are a = 5.3467(9), c = 7.0876(16) Å, V = 157.47(6) Å3, and Z = 2. The strongest reflections of the powder X-ray diffraction pattern [d,Å(I)(hkl)] are: 4.667(27)(100), 3.904(89)(101), 3.565(33)(002), 2.824(94)(102), 2.686(100)(110), and 1.939(35)(202). Metathénardite and thénardite clearly differ from one another in X-ray diffraction data and infrared and Raman spectra.

The new mineral pansnerite, ideally K3Na3Fe3+6(AsO4)8, was found in the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. It is associated with aphthitalite, hematite, sanidine, badalovite, khrenovite, achyrophanite, arsenatrotitanite, ozerovaite, tilasite, calciojohillerite, johillerite, nickenichite, svabite, katiarsite, yurmarinite, anhydrite, rutile, cassiterite and pseudobrookite. Pansnerite forms tabular to lamellar (flattened on {010}), usually pseudo-hexagonal crystals up to 0.2 mm × 0.7 mm × 1 mm and crystal clusters up to 2 mm across. It is transparent to translucent, light green, pale greenish, yellowish–greenish or yellowish, with vitreous lustre. The mineral is brittle, with perfect {010} cleavage. The Mohs’ hardness is ca 3. Dcalc is 3.596 g cm–3. Pansnerite is optically biaxial (–), α = 1.702(4), β = 1.713(4), γ = 1.717(4), 2Vmeas = 45(10)° and 2Vcalc = 62°. Chemical composition (holotype, wt.%, electron microprobe data) is: Na2O 6.39, K2O 8.52, CaO 0.08, MgO 0.08, MnO 0.02, NiO 0.02, CuO 1.35, ZnO 0.34, Al2O3 7.35, Cr2O3 0.04, Fe2O3 16.72, SiO2 0.16, P2O5 0.22, V2O5 0.09, As2O5 57.76, SO3 0.04, total 99.20. The empirical formula based on 32 O apfu is K2.86Na3.26Ca0.02(Fe3+3.31Al2.28Cu0.27Zn0.07Mg0.03Cr0.01)Σ5.97(As7.95P0.05Si0.04V0.02S0.01)Σ8.06O32. Pansnerite is orthorhombic, Cmce, a = 10.7372(3), b = 20.8367(8), c = 6.47335(15) Å, V = 1448.27(7) Å3 and Z = 2. The strongest reflections of the X-ray powder diffraction pattern [d,Å(I)(hkl)] are: 10.49(100)(020), 5.380(88)(111), 4.793(65)(220), 3.105(46)(311, 002), 3.079(32)(112, 061), 2.932(35)(260), 2.783(65)(202) and 2.694(52)(400, 222). The crystal structure was solved from single-crystal X-ray diffraction data, R1 = 2.82%. The structure is based on heteropolyhedral layers formed by MO6 octahedra (M = Fe3+ and Al) sharing common vertices and connected by AsO4 tetrahedra. Na+ and K+ cations are located in the interlayer space. The mineral is named in honour of the German–Russian mineralogist and geographer Lavrentiy Ivanovich Pansner (1777–1851). Pansnerite forms a solid-solution series with the isotypic mineral ozerovaite, ideally KNa2Al3(AsO4)4.

Unusual variety of forsterite strongly enriched by pentavalent constituents, phosphorus and arsenic (up to 12.9 wt% P2O5 and up to 16.0 wt% As2O5) was found in sublimates of the Arsenatnaya fumarole, Tolbachik volcano, Kamchatka, Russia, in association with As- and P-depleted forsterite, anhydrite, diopside, hematite, spinel, hauyne, fluorapatite, svabite, berzeliite, calciojohillerite, and arsenudinaite. This forsterite is the P-richest natural olivine which also demonstrates first case of As incorporation in an olivine-type silicate. P- and As-rich forsterite is orthorhombic, space group Pbnm, unit-cell parameters are: a = 4.7762(2), b =10.2643(4), c = 5.9646(2) A and V = 292.41(2) A3. Its crystal structure was solved on single crystal and refined to R = 2.88%. The crystal chemical formula is M(1)(Mg0.83[vac]0.17)M(2)(Mg0.95[vac]0.05)[Si0.56P0.32As0.12]O4. The substitution scheme for the incorporation of pentavalent constituents in forsterite is: VIMg2+ + 2IVSi4+ ↔ VI[vac]0 + 2IVT5+, in which T5+ = P, As and [vac] = vacancy. No sign of vacancies in the tetrahedrally coordinated T site is found.

Three samples of halurgite were re-examined: two from the Chelkar salt dome in the North Caspian Region, Western Kazakhstan (the type locality and including the type specimen), and one from a new locality in the Satimola salt dome located in the same region. The crystal structure of halurgite has been solved for the first time on the specimen from Chelkar with the empirical formula Mg3.94[B8.03O13.03(OH)1.97]2·7.16H2O; refinement began with single-crystal X-ray diffraction data and was subsequently refined on a powder sample using the Rietveld method (Rp= 0.0232,Rwp= 0.0354 andRobs= 0.0558). The idealised crystal chemical formula of halurgite is Mg4[B8O13(OH)2]2·7H2O. The mineral is monoclinic,P2/c,a= 13.201(2),b= 7.5622(10),c= 13.185(2) Å, β = 91.834(14)°,V= 1315.6(4) Å3andZ= 2. The crystal structure is unique. Eight B polyhedra form a fundamental building block [B8O16(OH)2], which is a six-membered borate ring (built by two pairs of B tetrahedra and two B triangles) with two additional triangular BO2(OH) groups. Each [B8O16(OH)2] ring is linked to six adjacent analogous rings to form a [B8O13(OH)2]∞layer. These layers are connectedviaMgO6and Mg(OH)2(H2O)4octahedra into a microporous heteropolyhedral pseudo-framework. The crystal structure of halurgite can also be described in terms of an approach developed for heterophyllosilicates containing three-layerHOHmodules, whereHOHrefers to an octahedral layerOsandwiched between two heteropolyhedral layersH. In halurgite theHOHmodule consists of two heteropolyhedral (BO3triangles + BO4tetrahedra) borateHlayers [B8O13(OH)2]∞and a central interruptedOlayer composed of MgO6octahedra, whereas a more voluminous Mg(OH)2(H2O)4octahedral complex and additional H2O molecules are located betweenHOHmodules. Halurgite and four related synthetic H-free boratesM2Cd3B16O28andM2Ca3B16O28(M= Rb or Cs) can be considered microporous heterophylloborates.

The new mineral zubkovaite, Ca3Cu3(AsO4)4, was found in the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. It is associated with anhydrite, svabite, hematite, johillerite, tilasite, fluorophlogopite, sanidine and aphthitalite. Zubkovaite occurs as coarse prismatic crystals up to 0.01 mm × 0.01 mm × 0.2 mm combined in radiating aggregates or crusts. The mineral is transparent, bright sky-blue, turquoise-coloured or light bluish-green, with vitreous lustre. It is brittle, with imperfect cleavage. The Mohs’ hardness isca3.Dcalcis 4.161 g cm–3. Zubkovaite is optically biaxial (–), α = 1.747(5), β = 1.774(5), γ = 1.792(5) and 2Vmeas= 75(10)°. Chemical composition (wt.%, electron microprobe) is: CaO 19.22, CuO 27.37, As2O552.54, SO30.67, total 99.80. The empirical formula based on 16 O apfu is Ca2.96Cu2.97(As3.945S0.07)Σ4.015O16. Zubkovaite is monoclinic,C2,a= 16.836(3),b= 5.0405(8),c= 9.1173(17) Å, β = 117.388(13)°,V= 687.0(2) Å3andZ= 2. The strongest reflections of the powder XRD pattern [d,Å (I) (hkl)] are: 7.44 (100) ($\bar 2$01), 3.727 (79) (400,$\bar 2$02,$\bar 3$11), 3.334 (92) ($\bar 1$12), 2.914 (73) (311), 2.765 (50) ($\bar 6$01,$\bar 6$02), 2.591 (96) ($\bar 3$13) and 2.521 (53) (020). The crystal structure is unique for minerals. It was solved from single-crystal X-ray diffraction data toR= 7.19%. The structure contains trimers of Cu2+-centred polyhedra (consisting of one distorted square CuO4in the core and two distorted square pyramids CuO5) and two crystallographically independent As5+O4tetrahedra playing different roles: As(2)O4tetrahedra link neighbouring trimers into ribbons whereas As(1)O4tetrahedra link adjacent ribbons into heteropolyhedral layers; Ca cations are located in the interlayer space. The mineral is named in honour of the Russian crystallographer and crystal chemist Natalia Vital'evna Zubkova (born 1976).

The crystal structure of manganonaujakasite was studied by single crystal X-ray analysis and infrared spectroscopy using a holotype sample with the empirical chemical formula (Na5.96Ca0.01) (Mn0.53Fe0.49)Al3.95Si8.03O26.00. The monoclinic unit cell parameters are: a = 15.029(1) A, b = 7.999(1) A, c = 10.467(1) A, β = 113.551(1)°; V = 1153.47(15) A3, space group C2/m, Z = 2. The microporous crystal structure of manganonaujakasite is similar to that of naujakasite and is based on tetrahedral [Al4Si8O26]-double layers which are linked via isolated (Mn,Fe)O6-octahedra to form a heteropolyhedral framework containing two systems of parallel wide channels. The naujakasite-type framework topologically relates to the ATV-type of AlPO4. Both are built from the same t-kah [63] and t-lov [42.62] tiles and are characterized by similar one-dimensional composite building units represented by the narsarsukite-type nsc-chain. The comparative data for the frameworks of naujakasite- and ATV-types are given.

Samarskite-(Y), the mineral known for almost 180 years only in metamict (X-ray amorphous) state, was found as non-metamict crystals in sanidinites of the Laach Lake (Laacher See), Eifel volcanic region, Germany. The crystal structure has been solved for the first time and refined to R1 = 1.1% based on 838 observed [I > 2σ(I)] independent reflections. Samarskite-(Y) is monoclinic, P2/c, a 9.8020(8), b 5.6248(3), c 5.2073(4) A, β 93.406(4)°, V 286.59(4) A3, Z = 2. The empirical formula (calculated on 8 O apfu) is $$\left[ {\left( {{\text{Y}}_{0. 2 5} Ln_{0. 1 8} } \right)_{\varSigma 0. 4 3} {\text{Th}}_{0. 3 7} {\text{U}}_{0. 1 3}^{ 4+ } {\text{Ca}}_{0.0 3} } \right]_{\varSigma 0. 9 6} \left( {{\text{Fe}}_{0. 7 3}^{ 3+ } {\text{Mn}}_{0. 1 8}^{ 2+ } } \right)_{\varSigma 0. 9 1} \left( {{\text{Nb}}_{ 1. 8 5} {\text{Ti}}_{0.0 6} {\text{Zr}}_{0.0 6} {\text{Ta}}_{0.0 3} {\text{W}}_{0.0 2} } \right)_{\varSigma 2.0 2} {\text{O}}_{ 8}$$ . Samarskite-(Y) from the type locality, the Blyumovskaya Pit, Ilmeny Mountains, South Urals, Russia, was studied for comparison; electron microprobe data showed the same species-defining constituents and stoichiometry: $$\left[ {\left( {{\text{Y}}_{0. 3 4} Ln_{0. 20} } \right)_{\varSigma 0. 5 4} {\text{U}}_{0. 4 2}^{ 4+ } {\text{Th}}_{0.0 3} } \right]_{\varSigma 0. 9 9} \left( {{\text{Fe}}_{0. 8 6}^{ 3+ } {\text{Mn}}_{0.0 8}^{ 2+ } } \right)_{\varSigma 0. 9 4} \left( {{\text{Nb}}_{ 1. 1 4} {\text{Ta}}_{0. 70} {\text{Ti}}_{0. 1 5} } \right)_{\varSigma 1. 9 9} {\text{O}}_{ 8}$$ . Samarskite-(Y) is the first example of cation-ordered niobate structurally related to layered double tungstates AMW2O8, the compounds used as luminophors and active media in solid-state lasers. The pseudo-layered framework of the mineral can be derived from that of wolframite via substitution of W for Nb, whereas each second [FeO6] layer is replaced by [YO8] one. The resulting sequence of layers can be expressed as -[AO8]-[BO6]-[MO6]-[BO6]- leading to the formula AMB2O8 in which A = Y, Ln, Th, U4+, Ca; M = Fe3+, Mn2+; and B = Nb, Ta, Ti. The end-member formula of samarskte-(Y) is YFe3+Nb2O8 (approved by the Commission on New Minerals, Nomenclature and Classification, International Mineralogical Association, memorandum 90-FH/18).

The new mineral antofagastaite, ideally Na2Ca(SO4)2·1.5H2O, was found in the oxidation zone of sulfide–quartz veins at the abandoned Coronel Manuel Rodríguez mine, Mejillones, Antofagasta Province, Antofagasta Region, Chile. It is associated with sideronatrite, metasideronatrite, aubertite, gypsum, ferrinatrite, glauberite, amarillite and an unidentified Fe phosphate. Antofagastaite occurs as prismatic crystals up to 0.5 mm × 1 mm × 5 mm, elongated along [010], typically combined in open-work aggregates up to 1 cm across. Antofagastaite is transparent and colourless, with vitreous lustre. It is brittle; the Mohs’ hardness isca3. Cleavage is distinct on (001).Dmeas.is 2.42(1) andDcalc.is 2.465 g cm−3. Antofagastaite is optically biaxial (–), α = 1.489(2), β = 1.508(2), γ = 1.510(2) and 2Vmeas.= 40(10)°. The IR spectrum is reported. Chemical composition (wt.%, electron microprobe, H2O determined by gas chromatography) is: Na2O 20.85, CaO 17.42, SO352.56, H2O 7.93, total 98.76. The empirical formula (based on 8 O atoms belonging to sulfate anions per formula unit with all H belonging to H2O molecules) is Na2.06Ca0.95S2.01O8·1.35H2O. Antofagastaite is monoclinic,P21/m,a= 6.4596(4),b= 6.8703(5),c= 9.4685(7) Å, β = 104.580(4)°,V= 406.67(5) Å3andZ= 2. The strongest reflections of the powder XRD pattern [d, Å (I, %) (hkl)] are: 9.17 (100) (001), 5.501 (57) (011), 3.437 (59) (020), 3.058 (43) (003), 2.918 (50) (2¯11), 2.795 (35) (013) and 2.753 (50) (121, 201). The crystal structure was solved based on single-crystal X-ray diffraction data,R1= 5.71%. The structure of antofagastaite consists of ordered and disordered blocks and is related to syngenite K2Ca(SO4)2·H2O. Incorporation of additional H2O molecules in the syngenite-type structure results in disorder of the one of the two tetrahedral sulfate groups occurring in antofagastaite. In addition to the above-reported type material, antofagastaite together with syngenite and blödite occurs in the Arsenatnaya fumarole, Tolbachik volcano, Kamchatka, Russia.

The crystal structure of hibbingite, natural γ-Fe2+ 2Cl(OH)3, a mineral of the atacamite group, was studied on a sample from the Oktyabr’sky mine, Norilsk district, Siberia, Russia. The structure was solved by direct methods based on single crystal X-ray diffraction data and refined to R=2.07% [520 reflections with I>2σ(I)]. The mineral is isostructural with atacamite and is orthorhombic, Pnma, a=6.3373(2), b=6.9892(2), c=9.3457(3) Å, V=413.95(3) Å3, Z=4. The structure contains Fe(1)(OH)4Cl2 octahedra which share Cl–O(1) edges to form chains running along the b axis and cross-linked by the chains of Fe(2)(OH)5Cl octahedra sharing O(2)–O(2) edges and running along the a axis.

The new mineral anatolyite Na6(Ca,Na)(Mg,Fe3+)3Al(AsO4)6 was found in the Arsenatnaya fumarole, Tolbachik volcano, Kamchatka, Russia. It is associated with potassic feldspar, hematite, tenorite, cassiterite, johillerite, tilasite, ericlaxmanite, lammerite, arsmirandite, sylvite, halite, aphthitalite, langbeinite, anhydrite, wulffite, krasheninnikovite, fluoborite, pseudobrookite and fluorophlogopite. Anatolyite occurs as aggregates (up to 2 mm across) of rhombohedral–prismatic, equant or slightly elongated along [001] crystals up to 0.2 mm. The mineral is transparent, pale brownish–pinkish, with vitreous lustre. It is brittle, cleavage was not observed and the fracture is uneven. The Mohs’ hardness is ca 4½. Dcalc is 3.872 g cm–3. Anatolyite is optically uniaxial (–), ω = 1.703(4) and ε = 1.675(3). Chemical composition (wt.%, electron microprobe) is: Na2O 16.55, K2O 0.43, CaO 2.49, MgO 5.80, MnO 0.16, CuO 0.69, ZnO 0.55, Al2O3 5.01, Fe2O3 7.94, TiO2 0.18, SnO2 0.17, SiO2 0.04, P2O5 0.55, As2O5 60.75, SO3 0.03, total 101.34. The empirical formula based on 24 O apfu is (Na5.90K0.10)Σ6.00(Ca0.50Na0.13Zn0.08Mn0.03)Σ0.74(Mg1.63Fe3+1.12Al0.15Cu0.10)Σ3.00(Al0.96Ti0.03Sn0.01)Σ1.00(As5.97P0.09Si0.01)Σ6.07O24. Anatolyite is trigonal, R$\bar{3}$c, a = 13.6574(10), c = 18.2349(17) Å, V = 2945.6(4) Å3 and Z = 6. The strongest reflections of the powder XRD pattern [d,Å(I)(hkl)] are: 7.21(33)(012), 4.539(16)(113), 4.347(27)(211), 3.421(20)(220), 3.196(31)(214), 2.981(17)(223), 2.827(100)(125) and 2.589(18)(410). The crystal structure was solved from single-crystal XRD data to R = 4.77%. The structure is based on a 3D heteropolyhedral framework formed by M4O18 clusters [M1 = Al and M2 = (Mg,Fe3+)] linked with AsO4 tetrahedra. (Ca,Na) and Na cations centre A1O6 and A2O8 polyhedra in voids of the framework. Anatolyite is isostructural with yurmarinite. The new mineral is named in honour of the outstanding Russian crystallographer, mineralogist and mathematician Anatoly Kapitonovich Boldyrev (1883–1946).

The new mineral kruijenite, ideally Ca4Al4(SO4)F2(OH)16·2H2O, was found in a calcic xenolith from tephra of the Feuerberg paleovolcano situated near Daun, Eifel paleovolcanic region, Rhineland-Palatinate, Germany. It is associated with fluorite, calcite, aragonite, cuspidine, magnesioferrite, hematite, sharyginite, harmunite, and an insufficiently investigated hydrous Ca-Mg-Al silicate. Kruijenite occurs as pale greenish-yellow to colourless long prismatic tetragonal crystals up to 0.1 mm × 1 mm in cavities typically combined in radiating or random aggregates. The mineral is brittle, with Mohs’ hardness of 3; Dcalc is 2.573 g/cm3. The IR spectrum is given. Kruijenite is optically uniaxial (−), ω = 1.576(3), e = 1.561(3). The chemical composition (wavelength dispersive spectrometer Oxford INCA Wave 700 EPMA analyser, H2O calculated from structural data) is: CaO 32.38 wt%, Al2O3 27.75 wt%, Cr2O3 1.45 wt%, SO3 8.09 wt%, F 5.84 wt%, H2O 25.64 wt%, –O=F –2.46 wt%, total 98.69 wt%. The empirical formula is Ca4.00(Al3.77Cr0.13)Σ3.90(SO4)0.70F2.13(OH)16.17·1.79H2O (Z = 2). Kruijenite is tetragonal, space group P4/ncc, a = 12.9299(4) A, c = 5.2791(3) A, V = 882.57(6) A3, Z = 2. The crystal structure was solved and refined to R = 0.121. Kruijenite represents a novel structure type. Its structure is based on the microporous pseudo-framework built by Al(OH)6 octahedra and CaF2(OH)6 polyhedra. The strongest reflections of the powder X-ray diffraction pattern [d (I) (hkl)] are: 9.12 A (77%) (110), 4.565 A (100%) (220), 4.084 A (50%) (310), 2.964 A (74%) (321), 2.694 A (27%) (411), 2.321 A (24%) (431), 2.284 A (29%) (511), 2.217 A (22%) (321, 530), 1.971 A (40%) (611). The mineral is named in honor of the Dutch collector of Eifel minerals Fred Kruijen (born in 1956).

The new mineral stefanweissite, IMA2018-020, was discovered in sanidinite volcanic ejecta from the Laach Lake (Laacher See) paleovolcano, Eifel region, Rhineland-Palatinate, Germany. Associated minerals are sanidine, nosean, biotite, augite, titanite, ferriallanite-(La), magnetite, baddeleyite and a pyrochlore-group mineral. Stefanweissite is brown and reddish-brown, with adamantine lustre; the streak is light brown to yellow. It forms long-prismatic crystals up to 0.03 mm × 0.07 mm × 1.0 mm and acicular crystals up to 2 mm long and 0.02 mm thick typically combined in radiated aggregates in cavities in sanidinite. Dcalc. = 5.254 g/cm3. The mean refractive index calculated from the Gladstone–Dale equation is 2.260. The Raman spectrum shows the absence of hydrogen-bearing groups. The chemical composition is (electron microprobe, wt.%): CaO 7.63, MnO 2.51, FeO 7.86, Al2O3 0.25, La2O3 2.28, Ce2O3 6.54, Pr2O3 1.01, Nd2O3 1.59, ThO2 3.71, UO2 1.09, TiO2 17.32, ZrO2 28.03, HfO2 0.91, Nb2O5 19.96, total 99.69. The empirical formula based on 14 O atoms per formula unit is Ca1.13(Ce0.33La0.12Nd0.08Pr0.05)Σ0.58Th0.12U0.03Mn0.29Fe0.91Al0.04Zr1.89Hf0.04Ti1.80Nb1.19O14. The simplified formula is (Ca,REE)2Zr2(Nb,Ti)(Ti,Nb)2Fe2+O14. Stefanweissite is orthorhombic, with space group Cmca. The unit-cell parameters are: a = 7.2896(4) Å, b = 14.1435(5) Å, c = 10.1713(4) Å and V = 1048.68(7) Å3. The crystal structure was solved using single-crystal X-ray diffraction data. Stefanweissite is an analogue of zirconolite-3O with Nb dominant over Ti in one of two octahedral sites. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 2.983(100)(202), 2.897(71)(042), 1.828(38)(154, 400, 333), 1.793(25)(244), 1.767(16)(080), 1.517(10)(282), 1.187(19)(483, 1.11.3, 602). Type material is deposited in the collections of the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, Russia, with the registration number 5191/1.

Dalnegorskite — the new pyroxenoid with the crystal-chemical formula Ca 2 Ca 2 MnCa(Si 3 O 9 ) 2 , and the simplified formula Ca 5 Mn(Si 3 O 9 ) 2 , is a rock-forming mineral in the boron-bearing calcareous skarns of the Dalnegorskoe boron-silicate deposit (Dalnegorsk, Primorsky Krai, Russia). It belongs to the structural type of bustamite and forms a continuous solid-solution series with the isostructural mineral ferrobustamite Ca 2 Ca 2 FeCa[Si 3 O 9 ] 2 . These pyroxenoids form thinly-radiated banded beige, pinkish-white and milky-white aggregates typically consisting of split thin acicular to fiber-like individuals and are associated with hedenbergite, datolite, andradite, galena, sphalerite, and pyrrhotite. D meas. = 3.02(2), D calc. = 3.035 g·cm –3 . Dalnegorskite is optically biaxial, negative, α = 1.640 (3), β = 1.647 (3), γ = 1.650 (3)°, 2 V meas. = 75(10)o. The average chemical composition of the holotype (electron microprobe data) is: MgO 0.23, CaO 40.02, MnO 5.02, FeO 3.64, SiO 2 50.65, total 99.56 wt.%. The empirical formula calculated on 18 O atoms is Ca 5.03 Mn 0.51 Fe 0.36 Mg 0.04 Si 6.03 O 18 . The crystal structure of the new mineral was refined by powder X-ray diffraction data using the Rietveld method, R p = 0.0345, R wp = 0.0444, R 1 = 0.0790, wR 2 = 0.0802. Dalnegorskite is triclinic, P -1, a = 7.2588(11), b = 7.8574(15), c = 7.8765(6) A, α = 88.550(15), β = 62.582(15), γ = 76.621(6)o, V = 386.23(11) A 3 , Z = 1. Dalnegorskite is distinctly different from the related mineral wollastonite in the infrared spectrum. The wave-numbers of maxima of strong bands in the characteristic region of Si—O stretching vibrations in the IR spectrum of dalnegorskite are (cm –1 ): 905, 937, 1025, 1070. The type specimen of dalnegorskite is deposited in the collection of the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, Russia (No. 96201).

In situ high-temperature powder X-ray diffraction (HTPXRD) and differential scanning calorimetry (DSC) of three natural borosilicates have been performed in the temperature range of 25—1200 °С. Axinite-(Mn) melts incongruently at 900 °С forming anorthite and bustamite. Leucosphenite decomposes at 850 °С to fresnoite and cristobalite. According to DSC data, kornerupine decomposes at 1177 °С and sapphirine, indialite, and spinel were observed as the products of kornerupine heating. The calculation and orientation of thermal expansion tensor have been performed using HTPXRD data. The study showed that the borosilicates expand weakly and almost isotropically. The average volumetric thermal expansion coefficients are 21.3, 22.7, and 32.9 ∙ 10 –6 °C –1 for axinite-(Mn), kornerupine, and leucosphenite, respectively. Leucosphenite has a maximum volumetric expansion most likely due to the pronounced layered character of the crystal structure. The least symmetric structure of axinite-(Mn) has the maximal anisotropy of thermal expansion in the temperature range of 600—900 °C.

Sodium plays an important role in the crystal structures of eudialyte-group minerals given that it can occupy different crystallographic sites. Predominantly, it distributes between the N(1–5) sites situated in the large cavities of the heteropolyhedral framework. Rarely, Na occupies split sites of the M(2) microregion where it can predominate over other elements (predominantly Mn, Fe2+, and Fe3+). The crystal structure of the Mn-deficient manganoeudialyte from the Lovozero alkaline complex (Kola Peninsula, Russia) has been refined. The trigonal unit–cell parameters are: a = 14.1848(2) Å, c = 30.4726(3) Å, V = 5309.90(11) Å3. The sample is a rare example of a high-sodium and high-calcium representative of the eudialyte group with Fe + Mn < 2 apfu. The idealized formula is Na14Ca6[(Mn,Fe)2Na]Zr3Si2[Si24O72]O(OH)·2H2O with bivalent components, Mn2+ and Fe2+, dominating at the M(2) site. The regularities of isomorphism involving M(2)Na in EGMs and the problem of the existence of the M(2)Na-dominant analogue of eudialyte are discussed. The new data obtained in this work confirm the previous conclusion that the complete isomorphism between Ca-deficient and Ca-rich members of the eudialyte group cannot be realized in frames of a single-space group (R3m, R-3m or R3). Thus, the existence of the M(2)Na analogue of eudialyte remains questionable.

Two new isostructural minerals udinaite and arsenudinaite with the end-member formulae NaMg4(VO4)3 and NaMg4(AsO4)3, respectively, are found in the Arsenatnaya fumarole, Tolbachik volcano, Kamchatka, Russia. They are associated with one another and anhydrite, diopside, hematite, schäferite, berzeliite, svabite, calciojohillerite, tilasite, reznitskyite, ludwigite, rhabdoborite-group borates, forsterite, magnesioferrite, fluorapatite, pliniusite, and powellite. Both minerals occur as equant tetragonal prismatic–dipyramidal crystals up to 0.15 mm, aggregates up to 1 cm and interrupted crusts up to 2 × 2 cm2. Udinaite and arsenudinaite, visually indistinguishable from one another, are transparent, beige or brownish-yellowish, with vitreous lustre. Both minerals are optically uniaxial (–); ω = 1.785/1.777 and ε = 1.830/1.820, Dcalc. = 3.613/3.816 g·cm−3 (udinaite/arsenudinaite). The empirical formulae are: udinaite: (Na0.55Ca0.16)Σ0.71(Mg4.04Mn0.02Fe0.01)Σ4.07(V1.63As1.05P0.28Si0.03S0.01)Σ3.00O12; arsenudinaite: (Na0.57Ca0.13)Σ0.70(Mg4.01Mn0.01Fe0.01)Σ4.03(As2.07V0.84P0.10Si0.01S0.01)Σ3.03O12. Both minerals are tetragonal, I-42d, Z = 4, a = 6.8011(2)/6.8022(1), c = 19.1839(12)/19.1843(6) Å, and V = 887.35(7)/887.66(4) Å3, R1 = 0.0287/0.0119 (udinaite/arsenudinaite). Their crystal structure consists of the helical chains of edge-sharing MgO6 octahedra and isolated TO4 tetrahedra, forming a heteropolyhedral pseudo-framework with Na cations located in cavities. Both minerals are isostructural to jeffbenite. Udinaite and arsenudinaite form an isomorphous series in which the contents of T constituents vary within (in apfu): V1.6–0.1As2.8–1.0P0.4–0.0.