The new eudialyte-group mineral amableite-(Ce), ideally Na15[(Ce1.5Na1.5)Mn3]Mn2Zr3□Si[Si24O69(OH)3](OH)2⋅H2O, was discovered in a peralkaline pegmatite at Saint-Amable Sill, Montérégie, Québec, Canada. The associated minerals are albite, microcline, aegirine, serandite, natrolite, yofortierite, and an unidentified titanosilicate forming minute grains. Amableite-(Ce) occurs as yellow equant or thick tabular crystals up to 2 mm across. The observed crystal forms are {0001}; the subordinate forms are {11$\bar{2}$0}, {10$\bar{1}$1}, and {10$\bar{1}$0}. Amableite-(Ce) is brittle, with a Mohs hardness of 5. D(meas) = 2.89(1), D(calc) = 2.899 g⋅cm–3. Amableite-(Ce) is optically anomalously biaxial (+) with α ≈ β = 1.603(2) and γ = 1.608(2). The chemical composition is (wt.%, electron microprobe, H2O measured by means of a modified Penfield method): Na2O 14.20, K2O 0.41, CaO 1.89, MnO 8.25, Fe2O3 2.40, La2O3 3.10, Ce2O3 4.19, Pr2O3 0.16, Nd2O3 0.59, SiO2 49.41, ZrO2 11.17, HfO2 0.24, TiO2 0.68, Nb2О5 1.54, Cl 0.26, H2O 1.70, –O≡Cl –0.06, total 100.13. The crystal structure was determined using single-crystal X-ray diffraction data and refined to R1 = 0.0423. Amableite-(Ce) is trigonal, space group R3, with a = 14.1340(3) Å, c = 30.3780(11) Å and V = 5255.6(3) Å3. The crystal-chemical formula is (Na12.93K0.27Ce0.06)Σ13.26[(Mn2.49Ce0.30Ca0.21)Σ3.00(Ce1.14Na1.04Ca0.82)Σ3.00](Mn1.05Fe0.90□1.05)Σ3.00(Zr2.85Ti0.12Hf0.03)Σ3.00(□0.40Nb0.36Si0.24)Σ1.00(Si0.88□0.12)Σ1.00[Si24(O70.44(OH)1.56)Σ72.00][(OH)2.20(H2O)1.27]Σ3.47Cl0.22 (Z = 3). Infrared and Raman spectra are given. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %)(hkl)] are: 11.34 (51)(101), 7.06 (76)(110), 4.312 (63)(205), 3.783 (38)(033), 3.538 (43)(027, 220), 2.963 (84)($\bar{3}$45), 2.837 (100)(404). The mineral is named after the discovery locality.

A new mineral cuprodobrovolskyite, ideally Na4Cu(SO4)3, was found in sublimates of 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 petrovite, saranchinaite, euchlorine, krasheninnikovite, langbeinite, calciolangbeinite, anhydrite, sanidine, tenorite and hematite. Cuprodobrovolskyite occurs as coarse hexagonal tabular or equant, typically skeletal crystals up to 1 mm and their clusters or crusts up to 1.5 cm × 2.5 cm in area. The mineral is transparent, light blue or greenish-bluish to almost colourless with vitreous lustre. Cuprodobrovolskyite is optically uniaxial (+) with ω = 1.509(3) and ε = 1.528(3). The empirical formula calculated on the basis of 12 O apfu is (Na3.64K0.09Pb0.03)Σ3.76(Cu0.51Ca0.22Mg0.16Zn0.07Al0.01Mn0.01)Σ0.98S3.04O12. The unit-cell parameters of cuprodobrovolskyite calculated from the powder X-ray diffraction data are: a = 15.702(2), c = 22.017(5) Å, V = 4701.0(2) Å3, space group R3 and Z = 18. The crystal structure was studied using the Rietveld method, Rp = 0.0246, Rwp = 0.0325, R1 = 0.0521 and wR2 = 0.0770. Cuprodobrovolskyite is an isostructural analogue of dobrovolskyite Na4Ca(SO4)3 with Cu prevailing over Ca. One of the main features of cuprodobrovolskyite is Cu2+ in 7-fold coordination. On the basis of relationships with saranchinaite Na2Cu(SO4)2 and petrovite Na12Cu2(SO4)8 in the Arsenatnaya fumarole and the results of heating experiments, cuprodobrovolskyite is considered as the highest-temperature phase among anhydrous Na–Cu sulfate minerals.

An investigation of sample 41647 from the Platinum Placer of Ugol'nyi Ruchei, Norilsk Cu–Ni deposit, Russia, stored in the systematic collection of the Fersman Mineralogical Museum, revealed that it contained a mineral that can be identified as the original stannopalladinite described in 1947. As the literature information on the latter is controversial, the mineral was re-investigated using modern analytical techniques. Stannopalladinite occurs as spherical and ovoid-shaped grains up to 0.08 mm, closely intergrown with tetraferroplatinum as part of flattened, prismatic crystals up to 6 mm long. The micro-indentation hardness of stannopalladinite (VHN, 30 g load) is 244 kg/mm2 (range 233–266, n = 4), corresponding to a Mohs hardness of 4. The calculated density is 9.781 g/cm3. In reflected light, stannopalladinite is pale pink. The bireflectance is noticeable only in oil immersion. In crossed nicols the mineral exhibits strong anisotropy with colour effects changing from reddish purple to greyish blue and polysynthetic twinning of grains. The reflectance curves show distinct anomalous dispersion. The chemical composition (wt.%, electron microprobe data, mean of 11 analyses) is: Cu 8.48, Pd 61.21, Pt 0.89, Sn 25.87, Pb 3.70, total 100.15. The empirical formula calculated on the basis of 4 atoms per formula unit is (Pd2.42Cu0.56Pt0.02)Σ3.00(Sn0.92Pb0.08)Σ1.00. The ideal chemical formula of stannopalladinite is therefore proposed as (Pd,Cu)3Sn instead of Pd3Sn2 used in the official IMA List of Minerals. The strongest powder X-ray diffraction lines are [dobs, Å (I, %) (hkl) ]: 2.292 (42) (231), 2.166 (100) (331), 2.034 (10) (710), 1.916 (15) (141) and 1.851 (15) (630). The powder X-ray data are indexed in the orthorhombic unit cell with a = 14.634(2), b = 8.5253(6), c = 4.5946(3) Å and V = 573.24(7) Å3 (Z = 8). Stannopalladinite can be reliably identified among all other minerals belonging to the binary Pd–Sn and ternary Pd–Cu–Sn systems by a combination of chemical, optical and X-ray data.

Mangani-eckermannite, ideally NaNa2(Mg4Mn3+)Si8O22(OH)2, is a new member of the amphibole supergroup found at Tanohata Mine, Shimohei District, Iwate Prefecture, Japan. It occurs as prismatic crystals up to 0.3 × 0.2 mm and their aggregates up to 1 mm intergrown with braunite, vittinkiite and quartz. Mangani-eckermannite is cherry-red to very dark red and reddish-brown in thicker grains. It is translucent with a pinkish white streak and vitreous lustre. It is brittle, fracture is stepped along crystal elongation and uneven across a crystal. Cleavage is perfect on {110}. Mohs hardness is 6. Dmeas = 3.16(2) and Dcalc = 3.186 g/cm3. The mineral is optically biaxial (–), with α = 1.645(3), β = 1.668(2), γ = 1.675(3) (589 nm); 2Vmeas = 60(10)°, 2Vcalc = 57°. The empirical formula derived from electron microprobe analysis, secondary-ion mass spectrometry and single-crystal structure refinement and calculated on the basis of 24 (O+OH) atoms per formula unit (apfu) is A(Na0.74K0.24□0.02)Σ1.00 B(Na1.52Ca0.24Mn2+0.24)Σ2.00 C(Mg2.54Mn2+1.45Mn3+0.71Fe3+0.26Ti0.04)Σ5.00 T(Si7.97Al0.03)Σ8.00O22W[(OH)1.52O0.48]Σ2.00. Mangani-eckermannite is monoclinic, space group C2/m, a = 9.9533(4), b = 18.1440(7), c = 5.2970(2) Å, β = 103.948(4)°, V = 928.39(6) Å3 and Z = 2. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %)(hkl)] are: 8.52(100)(110); 4.54(25)(040); 3.41(29)(131); 3.16(23)(310,201); 2.721(37)(151); 2.533(26)($\bar{2}$02). The crystal structure was refined to R1 = 0.0264 for 1001 independent reflections with I > 2σ(I). The place of mangani-eckermannite in the nomenclature of the amphibole supergroup is discussed and the status of mangano-ferri-eckermannite as a valid mineral species and successor of ‘kôzulite’ is questioned.

The new eudialyte-group mineral selsurtite, ideally (H3O)12Na3(Ca3Mn3)(Na2Fe)Zr3□Si[Si24O69(OH)3](OH)Cl⋅H2O, was discovered in metasomatic peralkaline rock from the Flora mountain, northern spur of the Selsurt mountain, Lovozero alkaline massif, Kola Peninsula, Russia. The associated minerals are aegirine, albite and orthoclase, as well as accessory lorenzenite, calciomurmanite, natrolite, lamprophyllite and sergevanite. Selsurtite occurs as brownish-red to reddish-orange, equant or flattened on (0001) crystals up to 2 mm across and elongate crystals up to 3 cm long. The main crystal forms are {0001}, {11$\bar{2}$0}, and {10$\bar{1}$1}. Selsurtite is brittle, with the Mohs’ hardness of 5. No cleavage is observed. Parting is distinct on (001). D(meas) = 2.73(2) and D(calc) = 2.722 g⋅cm–3. Selsurtite is optically uniaxial (–), with ω = 1.598(2) and ɛ = 1.595(2). The chemical composition is (wt.%, electron microprobe): Na2O 6.48, K2O 0.27, MgO 0.10, CaO 6.83, MnO 4.73, FeO 1.18, SrO 1.88, La2O3 0.57, Ce2O3 1.07, Pr2O3 0.20, Nd2O3 0.44, Al2O3 0.29, SiO2 50.81, ZrO2 13.50, HfO2 0.45, TiO2 0.61, Nb2О5 1.10, Cl 1.01, SO3 0.29, H2O 8.10, –O≡Cl –0.23, total 99.68. The empirical formula is H25.94Na6.03K0.16Mg0.07Ca3.51Sr0.52Ce0.19La0.10Nd0.08Pr0.03Mn1.91Fe0.47Ti0.22Zr3.16Hf0.06Nb0.24Si24.40Al0.16S0.10Cl0.82O79.13. The crystal structure was determined using single-crystal X-ray diffraction data and refined to R = 0.0484. Selsurtite is trigonal, space group R3, with a = 14.1475(7) Å, c = 30.3609(12) Å, V = 5262.65(7) Å3 and Z = 3. Infrared and Raman spectra show that hydronium cations are involved in very strong hydrogen bonds and form Zundel- and Eigen-like complexes. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %)(hkl)] are: 11.38 (56)(101), 7.08 (59)(110), 5.69 (36)(202), 4.318 (72)(205), 3.793 (36)(303), 3.544 (72)(027, 220, 009), 2.970 (100)(315) and 2.844 (100)(404). The mineral is named after the discovery locality.

A new mineral kalithallite, K3Tl3+Cl6⋅2H2O, was found in an active fumarole belonging to the Northern fumarole field at the First scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. Kalithallite is a product of the relatively low-temperature (70–150°C) interactions involving high-temperature sublimate minerals, volcanic gas and atmospheric water vapour. The associated minerals are cryobostryxite, KZnCl3⋅2H2O, halite, sylvite, opal and gypsum. Kalithallite forms lamellar to tabular crystals up to 5 × 30 × 40 μm combined in open-work aggregates up to 1 mm across. It is transparent, colourless in individuals and white to pale cream coloured or pale beige in aggregates, with vitreous lustre. Dcalc = 3.01 g cm–3. Kalithallite is optically uniaxial (–), ɛ = 1.656(3) and ω = 1.662(3). The chemical composition (wt.%, electron-microprobe data, H2O calculated by stoichiometry) is: K 17.72, Zn 0.85, Tl 38.76, Cl 35.91, H2Ocalc 5.99, total 99.23. The empirical formula calculated on the basis of K+Zn+Tl+Cl = 10 apfu is K2.72Zn0.06Tl1.14Cl6.08⋅2H2O. Kalithallite is tetragonal, I4/mmm, a = 15.9333(5), c = 18.1088(7) Å, V = 4595.2(4) Å3 and Z = 14. The strongest reflections of the powder X-ray diffraction (XRD) pattern [d,Å(I)(hkl)] are: 5.98(100)(202); 5.64(36)(220); 3.984(20)(400); 3.528(30)(224); 3.315(22)(422); 2.890(15)(334); and 2.817(24)(206, 440). Kalithallite is isotypical to synthetic K3Tl3+Cl6⋅2H2O. The crystal structure was refined from the powder XRD data using the Rietveld method, RBragg = 0.55%, Rp = 0.56%, and Rwp = 0.75%. The structure contains Tl3+Cl6 octahedra and K-centred polyhedra of three types: KCl8, KCl8(H2O) and KCl7(H2O)2. The mineral is named as a kalium–thallium ordered compound.

The new mineral axelite, ideally Na14Cu7(AsO4)8F2Cl2, 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 sylvite, halite, arsmirandite, bradaczekite, johillerite, tilasite, ericlaxmanite, lammerite, hematite, tenorite, cassiterite, pseudobrookite, aphthitalite-group sulfates, anhydrite, fluoborite, sanidine and fluorophlogopite. Axelite occurs as tabular, quadratic, rectangular or stronger distorted crystals up to 0.02 × 0.1 × 0.1 mm, sometimes combined in interrupted crusts up to 0.4 mm across overgrowing sylvite. It is transparent, sky-blue, with vitreous lustre. Cleavage was not observed. Dcalc is 3.662 g cm–3. Axelite is optically uniaxial (–), ɛ = 1.650(4) and ω = 1.678(4). Chemical composition (wt.%, electron microprobe data) is: Na2O 22.54, K2O 0.08, CaO 0.04, MgO 0.05, CuO 26.69, P2O5 1.75, V2O5 0.15, As2O5 44.14, SO3 0.04, F 1.57, Cl 3.60, –O=(F,Cl) –1.47, total 99.18. The empirical formula based on O+F+Cl=36 apfu is Na14.37K0.03Ca0.01Mg0.02Cu6.63P0.49V0.03As7.59S0.01O32.36F1.63Cl2.01. Axelite is tetragonal, P4bm, a = 14.5957(2), c = 8.34370(18) Å, V = 1777.51(6) Å3 and Z = 2. The strongest reflections of the powder X-ray diffraction (XRD) pattern [d,Å(I)(hkl)] are: 8.32(44)(001), 5.156(47)(220), 4.168(21)(002), 3.246(34)(222), 3.180(61)(331), 2.747(100)(402), 2.709(36)(511) and 2.580(29)(440). The crystal structure, solved from single-crystal XRD data (R = 4.50%), is unique. It is based on the heteropolyhedral chains built by clusters formed by CuO4Cl square pyramids connected with AsO4 tetrahedra. Adjacent chains are connected via common vertices of AsO4 tetrahedra with CuO4Cl pyramids to form a heteropolyhedral pseudo-framework. Axelite is remotely related, in both structural and chemical aspects, to lavendulan-like minerals and synthetic compounds. The mineral is named in honour of the outstanding Finnish–Russian crystallographer, mineralogist and material scientist Axel Gadolin (1828–1892).

The new alluaudite-group mineral khrenovite with the ideal, end-member formula Na3Fe3+2(AsO4)3 was found in the Arsenatnaya fumarole, Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. It is associated with aphthitalite-group sulfates, badalovite, calciojohillerite, nickenichite, johillerite, tilasite, svabite, achyrophanite, ozerovaite, pansnerite, arsenatrotitanite, anhydrite, sanidine, hematite, cassiterite, rutile and pseudobrookite. Khrenovite occurs as coarse prismatic crystals up to 0.2 × 0.3 × 0.8 mm and their clusters up to 1 mm across. It is transparent, honey-coloured, red-, orange- or yellow-brown, with vitreous lustre. Khrenovite is brittle, cleavage was not observed. Dcalc is 4.257 g cm–3. Khrenovite is optically biaxial (+), α = 1.825(7), β = 1.834(7), γ = 1.845(7) and 2Vmeas. = 80(10)°. The chemical composition (wt.%, electron-microprobe) is: Na2O 11.47, K2O 1.23, CaO 0.18, MgO 0.01, MnO 4.10, CuO 4.27, ZnO 1.99, Al2O3 0.17, Fe2O3 21.12, SiO2 0.08, P2O5 0.01, V2O5 0.10, As2O5 56.03, SO3 0.02, total 100.78. The empirical formula calculated on the basis of 12 O apfu is (Na2.26K0.16Ca0.02Mn0.35Cu0.33Zn0.15Al0.02Fe3+1.62)Σ4.91(As2.98Si0.01V0.01)Σ3.00O12. Khrenovite is monoclinic, C2/c, a = 12.2394(7), b = 12.7967(5), c = 6.6589(4) Å, β = 112.953(7)°, V = 960.37(10) Å3 and Z = 4. The crystal structure was solved from single-crystal X-ray diffraction data with R1 = 0.0287. Khrenovite is isostructural with other alluaudite-group minerals. Its structural formula simplified to the species-defining constituents is A(1)NaA(2)’NaM(1)NaM(2)Fe3+2(TAsO4)3. The mineral is named in honour of the Russian volcanologist and geologist Anatoly Petrovich Khrenov (1946–2016).

The new sodalite-group mineral bolotinaite, ideally (Na7□)(Al6Si6O24)F⋅4H2O, was discovered in a volcanic ejectum of trachitoid sanidinite collected from the In den Dellen (Zieglowski) pumice quarry, Laach Lake (Laacher See) palaeovolcano, Eifel region, Rhineland-Palatinate, Germany. The associated minerals are sanidine, nepheline, annite and zircon. Bolotinaite occurs as isolated interpenetration prismatic twins on (111) up to 1.3 mm long, complex twins, and rare non-twinned rhombic dodecahedra up to 0.2 mm across. The colour of bolotinaite is pale yellow to pinkish coloured, the streak is white and the lustre is vitreous. Weak orange–yellow fluorescence under longwave ultraviolet radiation (λ = 330 nm) is due to the presence of trace amounts of the S2•– radical anion. Bolotinaite is brittle, with a Mohs’ hardness of 5. No cleavage is observed. The fracture is uneven. D(meas) = 2.27(2) g⋅cm–3, D(calc) = 2.291 g⋅cm–3. Bolotinaite is optically isotropic, with n = 1.488(2) (λ = 589 nm). The chemical composition is (wt.%, electron microprobe, CO2 determined by quantitative IR spectroscopy analysis, H2O calculated from the empirical formula with four H2O molecules per formula unit): Na2O 18.30, K2O 3.87, CaO 0.57, Al2O3 28.85, SiO2 37.97, CO2 1.66, SO3 1.37, F 1.60, Cl 0.57, 2.22, H2O 7.21, –O≡(F,Cl) –0.80, total 101.17. The empirical formula is (Na5.92K0.82Ca0.10H0.08)(Si6.33Al5.67O24)(SO4)0.17F0.84Cl0.16(H2O)3.96(CO2)0.38. A high content of H2O and the presence of CO2 molecules and H+ cations as well as trace amounts of S2•– are confirmed by means of infrared and Raman spectroscopy. The crystal structure was determined using single-crystal X-ray diffraction data and refined to R = 0.0335. Bolotinaite is cubic, space group I$\bar{4}$3m, with a = 9.027(1) Å, V = 735.7(2) Å3 and Z = 1. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 6.36 (47) (110), 4.502 (10) (200), 3.679 (100) (211), 2.851 (28) (310), 2.603 (29) (222) and 2.126 (18) (330). The mineral is named in honour of the Russian crystallographer and crystal chemist Dr. Nadezhda Borisovna Bolotina (b. 1949).

Kaznakhtite, ideally Ni6Co3+2(CO3)(OH)16⋅4H2O, is a new member of the hydrotalcite group within the hydrotalcite supergroup. The mineral was discovered at the Kaznakhtinskiy ultrabasic massif, Altai Republic, SW Siberia, Russia. It occurs as powdery aggregates forming flattened lenses up to 1.5 × 0.5 cm and veinlets up to 1 cm long and up to 1 mm thick in aggregates of chrysotile, lizardite, stichtite and dolomite. Other associated minerals include brucite, chromite, heazlewoodite, manganochromite, magnetite and magnesioferrite. Kaznakhtite aggregates are composed of tiny platy grains up to 0.01 mm across. Kaznakhtite is light green and translucent in aggregates. It has an earthy lustre and white streak. Cleavage is micaceous on {001}. Dcalc = 2.864 g cm–3. The mineral is optically uniaxial (–) with ɛ = 1.657(3) and ω = 1.676(3), and weakly pleochroic in greenish hues, ω > ɛ. Chemical composition (wt.%, electron microprobe, Co valence state determined by XANES spectroscopy, CO2 and H2O calculated by stoichiometry) is: MgO 2.15, NiO 47.40, ZnO 0.22, Al2O3 0.16, Cr2O3 0.98, Co2O3 17.42, Cl 0.63, CO2 5.05, H2O 24.60, –O=Cl –0.14, total 98.47. The empirical formula calculated based on the sum of all metal cations = 8 apfu is (Ni5.54Mg0.47Zn0.02)Σ6.03(Co3+1.83Cr0.11Al0.03)Σ1.97C1.00O2.99(OH)15.84Cl0.16⋅4H2O. Infrared spectroscopy confirmed the presence of CO32– anions, OH– groups and H2O molecules. The crystal structure was refined by the Rietveld method with RB = 0.19%. Kaznakhtite is trigonal, space group R͞3m, a = 3.0515 (3), c = 23.180 (3) Å, V = 186.93 (4) Å3 and Z = 3/8. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 7.72 (100) (003); 3.863 (24) (006); 2.630 (4) (101); 2.576 (10) (012); 2.294 (6) (015); 1.950 (4) (018); 1.526 (4) (110); and 1.497 (4) (113). Kaznakhtite is a Co3+ analogue of reevesite, Ni6Fe3+2(CO3)(OH)16⋅4H2O. The mineral is named after its type locality.

Gurzhiite, ideally Al(UO2)(SO4)2F⋅10H2O, is a new uranyl sulfate mineral from the Bykogorskoe U deposit, Northern Caucasus, Russia. It occurs as fine-grained aggregates forming veinlets up to 50 cm long in cracks of the brecciated rock. Gurzhiite aggregates are composed of small bladed crystals up to 0.1 mm across. Associated minerals include khademite and quartz. Gurzhiite is pale yellow in crystals, lemon yellow in aggregates, transparent with a vitreous lustre and a white streak. It is brittle and has an irregular fracture. Cleavage is good on {001}. The new mineral exhibits a bright yellow–green fluorescence under both longwave and shortwave UV radiation. Mohs hardness is ~2. Dmeas = 2.52(3) g/cm3 and Dcalc = 2.605 g/cm3. The mineral is biaxial (–) with α = 1.528(3), β = 1.538(2), γ = 1.544(3) (589 nm); 2Vmeas= 80(10)° and 2Vcalc = 75.1°. The empirical formula calculated on the basis of 21(O + F) atoms per formula unit (apfu) is Al0.92Zn0.05Fe3+0.03Na0.03U0.95S2.00O9.85F0.99⋅10.16H2O. Gurzhiite is triclinic, with space group P$\bar{1}$, a = 7.193(2), b = 11.760(2), c = 11.792(2) Å, α = 67.20(3), β = 107.76(3), γ = 89.99(3)°, V = 867.7(4) Å3 and Z = 2. The five strongest lines of the powder X-ray diffraction pattern [d, Å (I, %)(hkl)] are: 10.24(100)(001); 5.40(14)($\bar{ 1}\bar{1}$1); 5.11(54)(002); 3.405(11)($\bar{2}$11); and 3.065(11)($\bar{1}\bar{1}$3). The crystal structure of gurzhiite is based upon uranyl sulfate chains of the same type as in bobcookite and svornostite. Between the chains are two types of Al-octahedra – Al1(H2O)6 and Al2F2(H2O)4. The entire structure stability is maintained by a complex network of H bonds. The new mineral honours Russian mineralogist and crystallographer Dr. Vladislav V. Gurzhiy in recognition for his contributions to uranium mineralogy and crystallography.

Calciolangbeinite, ideally K2Ca2(SO4)3, exists in two modifications, cubic and, first described in the present paper, orthorhombic. They are topologically-similar polymorphs which can be designated as calciolangbeinite-C and calciolangbeinite-O. Calciolangbeinite-O is the first natural orthorhombic langbeinite-like sulfate. It clearly differs from calciolangbeinite-C in the powder X-ray diffraction pattern, optical data and Raman spectrum. Calciolangbeinite-O is found in sublimates of the active Arsenatnaya fumarole at the Tolbachik volcano, Kamchatka, Far Eastern Region, Russia and in pyrometamorphic rocks of the Hatrurim Complex at Jabel Harmun, Judean Desert, Palestinian Autonomy and Har Parsa, Negev Desert, both in Israel. Calciolangbeinite-C is known only in fumarole sublimates at Tolbachik. Calciolangbeinite forms a continuous solid-solution system with langbeinite K2Mg2(SO4)3. The majority of the system is represented by cubic phases, and only members with compositions K2(Ca2.0–1.9Mg0.0–0.1)(SO4)3 have orthorhombic symmetry under room-temperature conditions. The crystal structure of calciolangbeinite-O was studied on a single crystal, chemically very close to K2Ca2(SO4)3, from Tolbachik (R1 = 2.75%). The unit-cell parameters are: a = 10.3330(2), b = 10.5027(2), c = 10.1763(2) Å, V = 1104.37(4) Å3 and Z = 4; space group is P212121. Calciolangbeinite-O is a low-temperature modification of K2Ca2(SO4)3 belonging to the K2Cd2(SO4)3 structure type whereas calciolangbeinite-C (space group P213), a high-temperature modification, has the langbeinite-type structure. The significant Mg admixture in calciolangbeinite-C from Tolbachik probably stabilises its cubic structure at room temperature. In both high-temperature fumaroles and pyrometamorphic rocks calciolangbeinite crystallises in the cubic modification, and during cooling its chemical variety close to the end-member K2Ca2(SO4)3 undergoes phase transition to calciolangbeinite-O, whereas the Mg-enriched varieties of the mineral remain calciolangbeinite-C.

The new alluaudite-group mineral paraberzeliite was found in the Arsenatnaya fumarole, Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. In the deepest zone of Arsenatnaya, paraberzeliite (holotype) is associated with anhydrite, diopside, hematite, svabite, berzeliite, schäferite, calciojohillerite, magnesioferrite, ludwigite, fluorapatite, powellite, baryte, and rhabdoborite-group and aphthitalite-group members. In the middle zone of the fumarole, paraberzeliite occurs with hematite, calciojohillerite, badalovite, johillerite, nickenichite, tilasite, svabite, fluorophlogopite, sanidine, cassiterite, anhydrite, metathénardite and belomarinaite. Paraberzeliite forms prismatic crystals up to 0.2 mm × 0.2 mm × 1 mm often occurring in open-work aggregates. It is transparent, brown (from light to dark brown, sometimes with purple or red hue) or green (from pale greenish to yellow–green). The mineral is brittle, cleavage was not observed. The Mohs hardness is 3½. Dcalc is 3.811 g cm–3. Paraberzeliite is optically biaxial (+), α = 1.718(4), β = 1.728(4), γ = 1.742(4) and 2Vmeas. = 85(5)°. The chemical composition (wt.%, electron-microprobe; holotype) is: Na2O 6.43, CaO 16.65, MgO 11.64, MnO 1.65, CuO 0.06, Fe2O3 2.45, V2O5 1.10, As2O5 59.46, total 99.44. The calculated empirical formula based on 12 O atoms per formula unit is (Na1.20Ca1.71Mg1.66Mn0.13Fe3+0.18)Σ4.88(As2.98V0.07)Σ3.05O12. Paraberzeliite is monoclinic, C2/c, a = 12.3143(7), b = 13.0679(5), c = 6.7717(4) Å, β = 113.657(7)°, V = 998.14(10) Å3 and Z = 4. The crystal structure was solved from single-crystal X-ray diffraction data, R = 0.0349. Paraberzeliite is isostructural with other alluaudite-group minerals. Its simplified crystal chemical formula is A(1)CaA(2)'NaM(1)CaM(2)Mg2(TAsO4)3. The idealised formula is NaCa2Mg2(AsO4)3, or, according to the actual nomenclature of alluaudite-group arsenates, NaCaCaMg2(AsO4)3. The name paraberzeliite reflects the dimorphism of this alluaudite-group mineral with the arsenate garnet berzeliite, ideally (Ca2Na)Mg2(AsO4)3.

The new sodalite-group mineral sapozhnikovite, ideally Na8(Al6Si6O24)(HS)2, was discovered in a hydrothermally altered urtite-like rock at Karnasurt Mountain, Lovozero alkaline massif, Kola Peninsula, Russia. The associated minerals are nepheline, aegirine, potassic feldspar, albite, kyanoxalite, natrolite, fluorapatite, fluorcaphite, lomonosovite (partially or completely altered to murmanite) and loparite-(Ce). Sapozhnikovite forms isolated colourless to pale greyish anhedral equant grains up to 5 mm across. The streak is white and the lustre is vitreous. Strong orange fluorescence under longwave UV radiation (λ = 330 nm) and weak yellow-orange fluorescence under shortwave UV radiation (λ = 245 nm) is observed. Sapozhnikovite is brittle, with a Mohs hardness of 5½. Cleavage is imperfect on (110). Density measured by flotation in heavy liquids is equal to 2.25(1) g⋅cm–3. The calculated density is 2.255 g⋅cm–3. Sapozhnikovite is characterised by infrared, Raman, electron spin resonance, NIR-Vis-UV absorption, and photoluminescence spectroscopy. The chemical composition is (wt.%, electron microprobe, H2O determined by gas chromatography of ignition products): Na2O 25.05, Al2O3 32.44, SiO2 37.58, HS 4.33, Cl 2.22, H2O 0.30, –O≡(Cl,HS) –1.55, total 100.37. The empirical formula is Na7.73Al6.08Si5.97O24(HS)1.25Cl0.60⋅0.16H2O. The crystal structure was determined using single-crystal X-ray diffraction data and refined to R1 = 1.62%. Sapozhnikovite is cubic, P$\bar{4}$3n, with a = 8.9146(1) Å, V = 708.45(2) Å3 and Z = 1. The new mineral is isostructural with sodalite. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 6.30 (37) (110), 3.638 (100) (211), 2.821 (14) (310), 2.572 (18) (222), 2.382 (16) (321) and 2.101 (29) (411). The mineral is named in honour of the Russian mineralogist and crystallographer Dr. Anatoly Nikolaevich Sapozhnikov (b. 1946).

The new wermlandite-group mineral erssonite, ideally CaMg7Fe3+2(OH)18(SO4)2⋅12H2O (or [Mg7Fe3+2(OH)18][Ca(SO4)2]⋅12H2O), was discovered in a late-stage, low-temperature assemblage in cavities of a magnetite-bearing dolomitic rock from the Långban deposit, Värmland county, Bergslagen ore province, Sweden. The associated minerals are dolomite, calcite, members of the magnetite–magnesioferrite solid-solution series, phlogopite, chrysotile, pyroaurite and norbergite. Erssonite has a vitreous lustre and forms colourless, platy hexagonal crystals flattened on [0001], up to 0.5 mm across and up to 10 μm thick, occurring mainly as aggregates in cavities of dolomitic rock. Erssonite is malleable; separate crystals are flexible and non-elastic, with a perfect, mica-like cleavage on {0001}. The calculated density is equal to 2.02 g⋅cm–3. Raman spectroscopy shows the presence of typical bands for S–O bonds attributed to intercalated SO42– anions and structural OH– anions together with the absence of C–O bonds, attributed to carbonate anions. The chemical composition is (wt.%, electron microprobe, H2O content is calculated from structure data): MgO 28.67, CaO 2.76, Al2O3 0.23, Cr2O3 0.23, Fe2O3 16.00, SiO2 0.48, SO3 14.80, H2O 35.58, total 98.75. The empirical formula based on 38 O atoms is H41.48Ca0.52Mg7.47Fe3+2.11Al0.05Cr0.03S1.94Si0.08O38. The ideal formula is CaMg7Fe3+2(OH)18(SO4)2⋅12H2O or {Mg7Fe3+2(OH)18}{[Ca(H2O)6](SO4)2(H2O)6}. The crystal structure was determined using single-crystal X-ray diffraction data and refined to R = 0.093. Erssonite is trigonal, P$\bar{3}$c1, with a = 9.3550(6), c = 22.5462(14) Å, V = 1708.8(2) Å3 and Z = 2. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %)(hkl)] are: 11.22 (90)(002), 5.63 (64)(004), 4.670 (100)(110, 104, 014), 2.626 (64)(032, 302), 2.435 (66)(034, 304) and 1.951 (45)(038, 308). The mineral is named in honour of the Swedish amateur mineralogist Dr. Anders Ersson (b. 1971).

Three new isostructural minerals, alexkuznetsovite-(La), ideally La2Mn(CO3)(Si2O7), alexkuznetsovite-(Ce) Ce2Mn(CO3)(Si2O7) and biraite-(La) La2Fe2+(CO3)(Si2O7), were discovered in polymineralic nodules from the Mochalin Log REE deposit, South Urals, Russia. The new minerals form anhedral grains up to 0.3 mm × 0.4 mm [alexkuznetsovite-(La)], 0.5 mm × 0.9 mm [alexkuznetsovite-(Ce)] and 0.2 mm × 1.2 mm [biraite-(La)] embedded in granular aggregates consisting of different REE minerals [allanite-(Ce)/-(La), bastnäsite-(Ce)/-(La), fluorbritholite-(Ce), perbøeite-(Ce)/-(La), percleveite-(Ce)/-(La) and törnebohmite-(Ce)/-(La)]. All three new species are brown to dark brown, translucent in thin fragments, with white streak, vitreous lustre and Mohs’ hardness of ~5. Dcalc = 4.713 [alexkuznetsovite-(La)], 4.687 [alexkuznetsovite-(Ce)] and 4.682 [biraite-La)] g⋅cm–3. Their empirical formulae, calculated on the basis of 2 Si and 10 O apfu, are: alexkuznetsovite-(La): (La0.98Ce0.89Nd0.10Pr0.05)Σ2.02Mn2+0.50Fe2+0.29Ca0.12Mg0.03(CO3)0.94(HCO3)0.06 (Si2O7); alexkuznetsovite-(Ce): (Ce0.96La0.78Nd0.16Pr0.07)Σ1.97Th0.01Mn2+0.50Fe2+0.33Ca0.14Mg0.02(CO3)0.93(HCO3)0.07(Si2O7); and biraite-(La): (La0.95Ce0.87Nd0.08Pr0.04)Σ1.94Th0.01Ca0.12Fe2+0.44Mn2+0.38Mg0.07(CO3)0.88(HCO3)0.12(Si2O7). The new minerals are monoclinic, P21/c and Z = 4. The unit-cell parameters of alexkuznetsovite-(La)/alexkuznetsovite-(Ce)/biraite-(La) are: a = 6.5642(3)/6.5764(4)/6.5660(10), b = 6.7689(3)/6.7685(4)/6.7666(11), c = 18.7213(10)/18.7493(15)/18.698(3) Å, β = 108.684(6)/108.672(8)/108.952(16)° and V = 788.00(7)/790.66(10)/785.7(2) Å3. The crystal structures are solved from single-crystal X-ray diffraction data; R = 0.0628 [alexkuznetsovite-(La)], 0.0589 [alexkuznetsovite-(Ce)] and 0.1193 [biraite-(La)]. A new biraite group is defined; it includes isostructural biraite-(Ce) and the three new minerals described herein. The rootname alexkuznetsovite is given in honour of the Russian mineral collector Alexey M. Kuznetsov (born 1962) who provided samples in which all three new minerals were found. The Levinson's suffix-modifier -(La) or -(Ce) indicates the predominance of La or Ce among REE in the mineral. Biraite-(La) is named as an analogue of biraite-(Ce) with La prevailing among REE.

The new mineral yurgensonite, ideally K2SnTiO2(AsO4)2, the first natural arsenate with species-defining tin, and the continuous isomorphous series between yurgensonite and katiarsite KTiO(AsO4) are described from sublimates of the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. Yurgensonite and a Sn-bearing variety of katiarsite are associated closely with one another and with badalovite, pansnerite, yurmarinite, achyrophanite, arsenatrotitanite, hatertite, khrenovite, svabite, sanidine, hematite, cassiterite, rutile and aphthitalite-group sulfates. Yurgensonite occurs as sword-shaped crystals up to 0.01 mm × 0.05 mm × 1 mm or acicular to hair-like individuals up to 1 mm long, typically forming radial aggregates up to 2 mm across. It is transparent, colourless, white or pale beige, with vitreous lustre. The mineral is brittle, cleavage was not observed. Dcalc is 3.877 g cm-3. Yurgensonite is optically biaxial (–), α = 1.764(6), β = 1.780(6), γ = 1.792(6) and 2Vmeas. is large. Chemical composition (wt.%, electron-microprobe; holotype) is: Na2O 0.51, K2O 16.27, Rb2O 0.12, Al2O3 0.26, Fe2O3 4.33, SiO2 0.29, TiO2 10.17, SnO2 22.01, P2O5 0.14, V2O5 0.19, As2O5 40.20, Sb2O5 4.88, SO3 0.28, total 99.65. The empirical formula based on 10 O apfu is (K1.92Na0.09Rb0.01)Σ2.02(Sn0.81Ti0.71Fe3+0.30Sb5+0.17Al0.03)Σ2.02(As1.945Si0.03S0.02P0.01V0.01)Σ2.015O10. Yurgensonite is orthorhombic, Pna21, a = 13.2681(6), b = 6.6209(3), c = 10.8113(5) Å, V = 949.74(7) Å3 and Z = 4. The crystal structure was solved from single-crystal X-ray diffraction data, R = 5.02%. Yurgensonite belongs to the KTP-structure type. It is a Ti,Sn-ordered analogue of katiarsite. The structure contains chains of corner-linked alternating crystallographically non-equivalent octahedra M(1) and M(2). In yurgensonite, Sn4+ prevails in the M(2)O6 octahedron whereas the M(1) site is Ti4+-dominant. The new mineral is named in honour of the Russian mineralogist, geochemist and specialist in studies of ore deposits Professor Georgiy Aleksandrovich Yurgenson (born 1935).

The new alluaudite-group mineral calciojohillerite is one of the major arsenates in sublimates of the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. In middle zones of the fumarole, calciojohillerite is associated with hematite, tenorite, johillerite, nickenichite, bradaczekite, badalovite, tilasite, lammerite, ericlaxmanite, aphthitalite-group sulfates, langbeinite, calciolangbeinite, anhydrite, sanidine, fluorophlogopite, fluoborite, cassiterite, pseudobrookite, rutile, sylvite and halite. In deep zones it occurs in association with anhydrite, diopside, hematite, svabite, berzeliite, schäferite, forsterite, magnesioferrite, ludwigite, rhabdoborite-group fluoroborates, powellite, baryte, fluorapatite, udinaite, arsenudinaite and paraberzeliite. Calciojohillerite forms prismatic crystals up to 1 cm long, their aggregates and crystal crusts up to 0.5 m2. It is transparent, colourless, pale green, pale yellow, light blue, pale lilac or pink, with vitreous lustre. The mineral is brittle, with imperfect cleavage. The Mohs hardness is 3½. Dcalc is 3.915 g cm–3. Calciojohillerite is optically biaxial (–), α = 1.719(3), β = γ = 1.732(3); 2Vmeas. = 15(10)°. Chemical composition (wt.%, electron-microprobe; holotype) is: Na2O 7.32, K2O 0.10, CaO 6.82, MgO 20.31, MnO 0.68, CuO 0.27, ZnO 0.02, Al2O3 0.56, Fe2O3 3.53, TiO2 0.01, SiO2 0.03, P2O5 1.25, V2O5 0.10, As2O5 58.77, SO3 0.13, total 99.90. The empirical formula based on 12 O atoms is (Na1.30K0.01Ca0.67Mg2.78Mn0.05Cu0.02Al0.06Fe3+0.24)Σ5.13(As2.83P0.10S0.01V0.01)Σ2.95O12. Calciojohillerite is monoclinic, C2/c, a = 11.8405(3), b = 12.7836(2), c = 6.69165(16) Å, β = 112.425(3)°, V = 936.29(4) Å3 and Z = 4. The crystal structure was solved from single-crystal X-ray diffraction data, R1 = 0.0227. Calciojohillerite is isostructural with other alluaudite-group minerals. Its simplified crystal chemical formula is A(1)CaA(1)′□A(2)□A(2)′NaM(1)MgM(2)Mg2(AsO4)3 (□ = vacancy). The idealised formula is NaCaMg3(AsO4)3, or, according to the nomenclature of alluaudite-group arsenates, NaCaMgMg2(AsO4)3. Calciojohillerite is named as an analogue of johillerite NaCu2+MgMg2(AsO4)3 with species-defining Ca instead of Cu in the ideal formula.

The new mineral percleveite-(La) (IMA2019–037), ideally La2Si2O7, was found in polymineralic nodules of the Mochalin Log REE deposit, Chelyabinsk Oblast, South Urals, Russia. It is associated with allanite-(Ce), allanite-(La), bastnäsite-(Ce), bastnäsite-(La), ferriallanite-(Ce), ferriallanite-(La), ferriperbøeite-(Ce), ferriperbøeite-(La), fluorbritholite-(Ce), hydroxylbastnäsite-(Ce), perbøeite-(Ce), perbøeite-(La), törnebohmite-(Ce) and törnebohmite-(La). Percleveite-(La) occurs as isolated anhedral grains commonly up to 0.2 mm × 0.4 mm and very rarely up to 1 mm × 1 mm. The new mineral is transparent with greasy lustre. The mineral is very pale yellow to colourless in thin fragments to light yellow in aggregates. It is brittle, with imperfect {001} cleavage and an uneven fracture. Mohs’ hardness is ca. 6. Dcalc = 5.094 g cm–3. Under the microscope, percleveite-(La) is non-pleochroic, optically uniaxial (+), ω = 1.825(10) and ɛ = 1.835(10). The Raman spectrum is given. Chemical data (wt.%, electron-microprobe) are: La2O3 36.80, Ce2O3 31.22, Pr2O3 1.57, Nd2O3 2.96, SiO2 26.73, total 99.28. The empirical formula based on 7 O apfu is (La1.02Ce0.86Nd0.08Pr0.04)Σ2.00Si2.00O7. Percleveite-(La) is tetragonal, P41; the unit-cell parameters are: a = 6.8482(3), c = 24.8550(13) Å, V = 1165.64(11) Å3 and Z = 8. The strongest reflections in the powder X-ray diffraction pattern [d, Å(I)(hkl)] are: 4.194(18)(113), 3.564(16)(106), 3.349(16)(201,202), 3.157(100)(203,116,008), 3.043(22)(211), 2.934(39)(122), 2.893(29)(213) and 2.864(21)(117). The crystal structure of percleveite-(La) is solved from the single-crystal X-ray diffraction data [R = 0.0617 for 2831 unique reflections with I > 2σ(I)]. The new mineral is named as an analogue of percleveite-(Ce) with La predominance over the rare-earth elements.