Strontioborite, which was first described in 1960 and later discredited by the then named Commission on New Minerals and Mineral Names of the International Mineralogical Association (IMA CNMMN), has been re-investigated (electron microprobe, single-crystal and powder X-ray diffraction, crystal structure determination and IR spectroscopy) on two specimens, including the holotype, and revalidated by the IMA Commission on New Minerals, Nomenclature and Classification (CNMNC). Strontioborite is known only at the Chelkar salt dome (North Caspian Region, Western Kazakhstan), in halite rocks with bischofite, magnesite, anhydrite, halurgite, boracite, ginorite and celestine. It forms colourless lamellar, scaly or tabular crystals up to 2 mm across. The chemical composition (wt.%, H2O is calculated for (OH)4 = 4 H apfu, according to structural data; holotype/neotype) is: CaO 1.42/0.27, SrO 23.10/23.79, B2O3 67.37/67.57, H2O 8.73/8.72, total 100.62/100.37. The empirical formulae [calculated based on 15 O apfu = O11(OH)4 pfu] of the holotype and neotype specimens are Sr0.92Ca0.10B7.98O11(OH)4 and Sr0.95Ca0.02B8.02O11(OH)4, respectively. The idealised formula is Sr[B8O11(OH)4]. Strontioborite is monoclinic, space group P21, a = 7.6192(3), b = 8.1867(2), c = 9.9164(3) Å, β = 108.357(4)°, V = 587.07(3) Å3 and Z = 2. The strongest reflections of the powder X-ray diffraction pattern [d,Å(I)(hkl)] are: 7.22(100)(100), 5.409(61)(110), 4.090(64)(020), 3.300(48)(210), 2.121(30)($\bar{1}$24) and 2.043(37)(040, 024, $\bar{2}$24). The crystal structure, solved from single-crystal X-ray diffraction data (R = 0.0372), is based upon the (100) layers of polymerised B–O–OH polyanions [B8O11(OH)4]2– and Sr-centred nine-fold polyhedra SrO6(OH)3. The B–O–OH polyanion is the cluster of three tetrahedra and three triangles; these clusters are decorated by the [B2O2(OH)3] pyro-group consisting of two triangles. The layers are linked via vertices of Sr-centred polyhedra, which share seven vertices with B-centred polyhedra of one layer and two vertices with B-centred polyhedra of the adjacent layer, and by the system of H bonds. The crystal chemistry of strontioborite is discussed in comparison with other natural and synthetic borates.

Hydroxylbastnäsite-(La), the OH- and La-dominant member of the bastnäsite group, in fact known for many years, was studied in detail and has been approved by the IMA–CNMNC as a new mineral species with the ideal, end-member formula La(CO3)(OH). The holotype originates from the Vuoriyarvi (another spelling: Vuorijärvi) alkaline-ultrabasic complex, Northern Karelia, and the cotype from the Mochalin Log REE deposit, Potaniny Mts, South Urals, both in Russia. At Vuoriyarvi, hydroxylbastnäsite-(La) occurs as clusters (up to 1 mm) of light brown, honey-yellow or colourless hexagonal tabular to short-prismatic crystals up to 0.15 mm associated with fluorite and ancylite-(Ce) in cavities of calcite–dolomite carbonatites. At Mochalin Log, hydroxylbastnäsite-(La) forms light brown grains up to 0.2 mm included in massive aggregates of other LREE minerals: bastnäsite-(Ce), bastnäsite-(La), percleveite-(Ce), percleveite-(La), biraite-(Ce), biraite-(La), törnebohmite-(La), ferriperbøeite-(Ce), allanite-(Ce), etc. Dmeas is 4.75(2) and Dcalc is 4.778 g cm–3 (holotype). Hydroxylbastnäsite-(La) is optically uniaxial (+), ω = 1.76(1) and ε = 1.86(1) (holotype). The chemical composition (wt.%, electron microprobe, CO2 and H2O calculated: holotype/cotype) is: CaO 0.23/0.00, SrO 0.07/0.00, La2O3 39.47/39.58, Ce2O3 33.51/31.99, Pr2O3 1.03/1.51, Nd2O3 1.95/2.38, F 0.76/3.33, CO2 20.49/20.34, H2O 3.77/2.58, –O=F 0.32/1.40, total 100.96/100.31. The empirical formulae, calculated based on the sum of metal cations of 1 apfu and one CO3 group pfu, are (La0.52Ce0.44Nd0.02Pr0.01Ca0.01)Σ1.00(CO3)[(OH)0.90F0.09]Σ0.99 (holotype) and (La0.53Ce0.42Nd0.03Pr0.02)Σ1.00(CO3)[(OH)0.62F0.38]Σ1.00 (cotype). Hydroxylbastnäsite-(La) is hexagonal, P6̅, unit-cell parameters (from powder XRD data, holotype/cotype) are: a = 12.537(3)/12.533(1), c = 9.968(2)/9.908(1) Å, V = 1356.8(5)/1347.9(3) Å3 and Z = 18. Strong reflections of the powder XRD pattern [d,Å(I)(hkl)] are (holotype): 4.98(39)(002), 3.616(88)(300), 2.926(100)(302), 2.089(41)(330), 2.052(46)(304) and 1.927(40)(332). The crystal structure of holotype hydroxylbastnäsite-(La) was refined by the Rietveld method, Rwp = 0.0071, Rp = 0.0050, Robs = 0.0466. It is isostructural to hydroxylbastnäsite-(Ce) and synthetic bastnäsite-type hydroxyl-carbonates REE3+(CO3)(OH) (REE = La–Er), but differs from fluorine-dominant bastnäsites which adopt the space group P6̅2c.

The new ludwigite-group mineral savelievaite, ideally Mg2Cr3+O2(BO3), was found in the chromitite body at the Malaya Kharamatalou river valley, Voikar–Syninskiy ultrabasic complex, Polar Urals, Russia. Savelievaite and Cr-enriched ludwigite occur in clinochlore veinlets and are associated with earlier magnesiochromite, spinel, chromite, pargasite, diopside, forsterite, serpentine, magnetite and pentlandite. Savelievaite forms prismatic, acicular or fibrous crystals up to 0.05 × 0.4 mm, usually assembled in radiating or chaotic clusters up to 1 × 1.5 mm across. It is opaque, black to greenish-black. The lustre is vitreous for prismatic crystals and silky for fibrous aggregates. D(calc.) = 3.91 g cm–3. Under the microscope in reflected light, savelievaite is grey, non-pleochroic, with weak bireflectance and anisotropism. The chemical composition (wt.%, EMPA, Fe2+:Fe3+ ratio by stoichiometry) is: MgO 34.88, FeO 10.83, NiO 0.36, B2O3 16.80, Al2O3 2.97, V2O3 0.21, Cr2O3 21.97, Fe2O3 12.40, TiO2 0.43, total 100.85. The empirical formula calculated on the basis of 5 O apfu is (Mg1.72Fe2+0.30Ni0.01)Σ2.03(Cr3+0.57Fe3+0.31Al0.12Ti0.01V3+0.01)Σ1.02B0.96O5. Savelievaite is orthorhombic, space group Pbam, a = 9.2631(6), b = 12.2298(8), c = 3.0104(2) Å, V = 341.04(4) Å3 and Z = 4. The strongest reflections of the powder X-ray diffraction pattern [d,Å(I)(hkl)] are: 5.101(100)(120); 2.551(90)(240); 2.524(88)(201); 2.163(36)(250); and 2.033(55)(321). The crystal structure was solved from single-crystal X-ray diffraction data and refined to R1 = 0.0405. Savelievaite is isostructural with ludwigite, Cr3+ is concentrated at the M4 site. The mineral is named in honour of the Russian petrologist and geologist Dr. Galina Nikolaevna Savelieva (b. 1936). Ludwigite, ideally Mg2Fe3+O2(BO3), and savelievaite form a continuous isomorphous series in which Cr3+ content varies from 0 to 0.60 apfu. Occurrences of Cr-enriched (>1 wt.% Cr2O3) varieties of ludwigite are mainly related to ultrabasic complexes. The Cr-richest (>10 wt.% Cr2O3) ludwigite–savelievaite-series members are found in chromite ores at the Voikar–Syninskiy complex and Volchiegorskoe and Tatishchevskoe deposits, both in the South Urals.

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.

The new mineral evseevite was found in the Arsenatnaya fumarole, Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. Evseevite is represented by two chemical varieties. The variety close to the end-member Na2Mg(AsO4)F (holotype) is associated with sanidine, hematite, tenorite, aegirine, cassiterite, sylvite, halite, johillerite, badalovite, calciojohillerite, hatertite, arsmirandite, yurmarinite, axelite, polyarsite, aphthitalite, potassic-magnesio-fluoro-arfvedsonite, litidionite, ferrisanidine and tridymite. The P- and S-enriched variety (cotype) is associated with hematite, fluorophlogopite, svabite, fluorapatite, tilasite, calciojohillerite, forsterite, cassiterite, belomarinaite and aphthitalite. Evseevite occurs as prismatic, acicular or hair-like crystals up to 0.7 mm long combined in clusters up to 0.5 mm, brushes or crusts up to 2 × 2 mm. It is transparent, colourless or pale pinkish, with vitreous lustre. Dcalc is 3.377 g cm–3 for the holotype and 3.226 g cm–3 for the cotype. Evseevite is optically uniaxial (+), α = 1.545(2), β = 1.546(2), γ = 1.549(2) and 2Vmeas = 40(10)°. The empirical formulae calculated based on O+F = 5 apfu are (Na1.99Ca0.03K0.01)Σ2.03(Mg0.98Fe3+0.01Zn0.01Cu0.01)Σ1.01[(As0.98Si0.01)Σ1.01O4](F0.97O0.03) for the holotype and Na2.02(Mg1.00Fe3+0.03)Σ1.03[(As0.69P0.25S0.07)Σ1.01O4](F0.78O0.22) for the cotype. Evseevite is orthorhombic, Pbcn, a = 5.3224(1), b = 14.1255(3), c = 12.0047(3) Å, V = 902.53(4) Å3 and Z = 8. Strong reflections of the powder XRD pattern [d,Å(I)(hkl)] are: 4.001(100)(121), 3.479(56)(023), 3.041(45)(042), 2.657(44)(200), 2.642(68)(142) and 2.613(36)(104). The crystal structure was solved from single-crystal XRD data and refined on powder data by the Rietveld method, Rwp = 0.0068, Rp = 0.0047 and Robs = 0.0435. Evseevite is isostructural to moraskoite Na2Mg(PO4)F. The structure of evseevite can be described in terms of anion-centred polyhedra. F-centred octahedra [FNa4Mg2]7+ share faces to form chains [FNa2Mg]3+ and AsO4 tetrahedra are located between the chains. Evseevite belongs to a small set of minerals with antiperovskite structures and is the first natural arsenate with antiperovskite units. The mineral is named in honour of the Russian mineralogist Aleksandr Andreevich Evseev (born 1949).

The new mineral bakakinite, ideally Ca2V2O7, was found in the high-temperature (not lower than 500°C) exhalations 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 anhydrite, svabite, pliniusite, schäferite, berzeliite, diopside, hematite, powellite, baryte, fluorapatite, calciojohillerite, ludwigite, magnesioferrite, anorthite, titanite and esseneite. Bakakinite forms flattened crystals up to 30 × 5 μm, typically distorted. The mineral is transparent, colourless or pale yellow, with strong vitreous lustre. Electron microprobe analysis gave (wt.%): CaO 37.04, SrO 0.26, SiO2 0.16, P2O5 1.48, V2O5 49.47, As2O5 10.85, SO3 0.35, total 99.61. The empirical formula calculated on the basis of 7 O apfu is (Ca1.99Sr0.01)Σ2.00(V1.64As0.28P0.06Si0.01S0.01)Σ2.00O7. The Dcalc is 3.463 g cm–3. Bakakinite is triclinic, P$\bar{1}$, unit-cell parameters are: a = 6.64(2), b = 6.92(2), c = 7.01(2) Å, α = 86.59(7), β = 63.77(7), γ = 83.47(6)°, V = 287.0(5) Å3 and Z = 2. The strongest reflections of the powder X-ray diffraction pattern [d,Å(I)(hkl)] are: 4.647(27)(111, 0$\bar{1}$1), 3.138(76)(002), 3.103(100)(120, 121), 3.027(20)(021), 2.960(81)(200), 2.158(19)(031, 302), 1.791(16)(320), 1.682(16)(114) and 1.584(17)(1$\bar{3}$3, 403). Bakakinite is a natural analogue of synthetic Ca2V2O7. The mineral is named in honour of the outstanding Russian crystallographer and crystal chemist Vladimir Vasilievich Bakakin (born 1933).

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.

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).

Zaykovite, ideally Rh3Se4, is a new mineral, the first natural rhodium selenide. It was discovered in the assemblages of platinum-group minerals from the Kazan gold placer, South Urals, Russia. The mineral occurs as crystals up to 40 μm in size within the grains of Pt3Fe alloy, in association with unnamed Pd–Sb–Te phase and Au–Pd alloy. In reflected light, zaykovite has a grey colour with bluish-greenish tint; it shows weak bireflectance and anisotropy. Reflectance values [Rmax/Rmin (%) for COM approved wavelengths (nm)] are: 30.1/29.3(470), 32.2/31.0(546), 33.4/32.0(589) and 35.1/33.7(650). The chemical composition corresponds to the empirical formula (Rh2.26Pt0.46Ir0.25Ru0.01Pd0.01Fe0.01)Σ3.00(Se2.77S1.21Te0.02)Σ4.00 Zaykovite is monoclinic, space group C2/m, a = 10.877(1), b = 11.192(1), c = 6.4796(6) Å, β = 108.887(2)°, V = 746.3(1) Å3, Z = 6 and Dcalc = 8.32 g cm–1. The crystal structure has been solved and refined to R1 = 0.016 based on 858 unique observed reflections. The strongest lines of the powder X-ray diffraction pattern [d(Å), (I), (hkl)] are: 5.43(37)($\bar{1}$11), 3.275(75)(310), 3.199(100)($\bar{1}$31), 3.061(87)(002), 2.568(62)(400), 2.545(41)(041), 3.413(34)($\bar{2}$41) and 1.697(34)(441). Zaykovite is a Se analogue of kingstonite, Rh3S4. A continuous series of solid solutions between kingstonite and zaykovite was encountered in the samples from the Kazan placer. The possible sources of this unique Rh–Se mineralisation in the South Urals could be serpentinised dunite–harzburgite or gabbro–clinopyroxenite–dunite complexes in the vicinity.

The columbite supergroup is established. It includes five mineral groups (ixiolite, wolframite, samarskite, columbite and wodginite) and one ungrouped species (lithiotantite). The criteria for a mineral to belong to the columbite supergroup are: the general stoichiometry MO2; the crystal structure based on the hexagonal close packing (hcp) of anions (or close to it); the six-fold coordination number of M-type cations (augmented to eight-fold in the case of slight distortion of hcp); and the presence of zig-zag chains of edge-sharing M-centred polyhedra. The ixiolite-type structure is considered as an aristotype with the space group Pbcn, the smallest unit cell volume, and the basic vectors a0, b0 and c0. Based on the multiplying of the ixiolite-type unit cell the following derivatives are distinguished: ixiolite type [ixiolite-group minerals; a = a0, b = b0 and c = c0; space group Pbcn; the members are ixiolite-(Mn2+), ixiolite-(Fe2+), scrutinyite, seifertite and srilankite]; wolframite type [wolframite-group minerals, ordered analogues of the ixiolite type with a = a0, b = b0 and c = c0; P2/c; the members are ferberite, hübnerite, huanzalaite, sanmartinite, heftetjernite, nioboheftetjernite, rossovskyite and riesite]; samarskite type [samarskite-group minerals; a = 2a0, b = b0 and c = c0; P2/c; the members are samarskite-(Y), ekebergite and shakhdaraite-(Y)]; columbite type [columbite-group minerals; a = 3a0, b = b0 and c = c0; Pbcn; the members are columbite-(Fe), columbite-(Mn), columbite-(Mg), tantalite-(Fe), tantalite-(Mn), tantalite-(Mg), fersmite, euxenite-(Y), tanteuxenite-(Y) and uranopolycrase]; and wodginite type [wodginite-group minerals; a = 2a0, b = 2b0 and c = c0; C2/c; the members are wodginite, ferrowodginite, titanowodginite, ferrotitanowodginite, tantalowodginite, lithiowodginite and achalaite]. Samarskite-(Yb), ishikawaite and calciosamarskite are insufficiently studied, tentatively considered as possible members of the samarskite supergroup. Qitianlingite, yttrocolumbite-(Y), yttrotantalite-(Y) and yttrocrasite-(Y) are questionable and need further studies. Polycrase-(Y) is discredited as identical to euxenite-(Y). Ixiolite has been renamed as ixiolite-(Mn2+), with the end-member formula (Ta2/3Mn2+1/3)O2. Ta- and Nb-dominant analogues of ixiolite with different schemes of charge balancing have the end-member formulae (M15+0.5M23+0.5)O2, M15+2/3M22+1/3)O2, M15+0.75M2+0.25)O2 or M15+0.8□0.2)O2 and the root name ‘ixiolite’ (for M1 = Ta) or ‘nioboixiolite’ (for M1 = Nb).

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.

Nickolayite, FeMoP, is a new terrestrial phosphide structurally related to allabogdanite (high-pressure modification of (Fe,Ni)2P), and the meteoritic phosphides florenskyite, FeTiP and andreyivanovite, FeCrP. From the point of view of chemical composition, nickolayite is an Fe-analogue of monipite, MoNiP. The mineral was discovered in the Daba-Siwaqa complex, Central Jordan, a part of the pyrometamorphic Hatrurim Formation (the Mottled Zone), whose outcrops encompass a 150 × 200 km area around the Dead Sea in the Middle East. Nickolayite appears as an accessory phase in the fused clinopyroxene–plagioclase rocks texturally resembling gabbro–dolerite. The irregularly shaped grains of the mineral, up to 80 μm in size are associated with baryte, tridymite, chromite, hematite, pyrrhotite, fluorapatite, titanite and powellite. Macroscopically, nickolayite grains possess light-grey to greyish-white colour and metallic lustre. The mineral is ductile. The mean VHN hardness (50 g load) is 538 kg mm–2. The calculated density based on the empirical formula and the unit-cell parameters is 7.819 g cm–1. In reflected light, nickolayite has a white colour, with no bireflectance or pleochroism. The COM approved reflectance values [Rmax/Rmin (%), λ(nm)] are: 48.5/46.5 (470), 50.5/48.5 (546), 51.8/49.9 (589) and 53.9/52.0 (650). The chemical composition of the holotype crystal is (electron microprobe, average of 4 analyses, wt.%): Fe 32.21, Mo 47.06, Ni 3.69, Co 0.13, P 17.45, total 100.54, that corresponds to the empirical formula Fe1.00(Mo0.87Ni0.11Fe0.02)Σ1.00P1.00 and an ideal formula of FeMoP. Nickolayite is orthorhombic, space group Pnma, unit-cell parameters of holotype material are: a = 5.9519(5), b = 3.7070(3), c = 6.8465(6) Å, V = 151.06(2) Å3 and Z = 4. The crystal structure of holotype material was solved and refined to R1 = 0.0174 based on 251 unique observed reflections. The origin of the mineral is probably connected to the processes of co-reduction of molybdenum- and phosphorus-bearing minerals during high-temperature pyrometamorphic processes.

Medvedevite, KMn2+V5+2O6Cl⋅2H2O, is a new mineral discovered in the Toludskoe lava field, formed during the 2012–2013 Tolbachik fissure eruption. The mineral occurs as thin acicular transparent bright red crystals up to 0.15 mm. Medvedevite is associated with thénardite, halite, aphthitalite, leonite, kieserite, eugsterite and syngenite. The empirical formula calculated on the basis of 13+ positive charge units for the anhydrous part and 2H2O is (K1.02Na0.03)Σ1.05Mn2+0.95(V5+1.92S6+0.05Si0.04)Σ2.01O6.02Cl0.96⋅2H2O. The crystal structure of medvedevite was determined using single-crystal X-ray diffraction data: monoclinic crystal system, the space group is P21/c, a = 7.1863(2), b = 10.1147(3), c = 12.7252(4) Å, β = 106.243(3)°, V = 888.04(5) Å3, Z = 4 and R1 = 0.029. The concept of ‘structural unit’ and ‘interstitial complex’ could be applied to the crystal structure of medvedevite. The structural units in medvedevite are based on the high bond-valence V5+O5 polyhedra which share edges and link into [V2O6] chains elongated along the a axis. The interstitial complexes consist of Mn2+, K+ cations and H2O groups and occupy the interstices between structural units. The mineral is optically biaxial (+), with α =1.782(2), β = 1.786(2), γ = 1.792(2), 2V(calc) = 41° (λ = 589 nm). The seven strongest lines of the powder XRD pattern are [d, Å (I, %) (hkl)]: 7.79(100)(011); 5.70(11)(110); 4.75(14)(11$\bar{2}$); 3.89(29)(022); 3.25(53)(031); 2.958(79)(21$\bar{3}$); and 2.850(33)(220). The mineral has been named in honour of the Russian geologist and chemist Robert Alexandrovich Medvedev (1939–2005).

Reznitskyite, ideally CaMg(VO4)F, is a new mineral species of the tilasite group from the Arsenatnaya fumarole, Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. It occurs as zones (usually up to 0.05 mm thick) in crystals of V- and P-containing tilasite or as homogeneous grains up to 0.1 mm across. It was found in polymineralic sublimate encrustations in association with minerals of the svabite–fluorapatite–pliniusite system and the schäferite–berzeliite, tilasite–isokite, wagnerite–arsenowagnerite and udinaite–arsenudinaite series. The mineral assemblage also includes calciojohillerite, diopside, forsterite, titanite, rhabdoborite-(V), rhabdoborite-(W), rhabdoborite-(Mo), ludwigite, powellite, scheelite, hematite, baryte and magnesioferrite. Reznitskyite is transparent or semi-transparent, colourless, with vitreous lustre. Dcalc. = 3.453 g cm–3. Under the microscope, in reflected light reznitskyite is grey, non-pleochroic, with very weak bireflectance (ΔR589 nm = 0.5%) and distinct anisotropy. Reznitskyite is the first vanadate with a titanite-type structure. It is monoclinic, space group C2/c, a = 6.6912(7), b = 8.9395(7), c = 7.0587(8) Å, β = 113.078(13)°, V = 388.43(8) Å3 and Z = 4. The strongest reflections of the powder X-ray diffraction pattern are [d in Å(I)(hkl)]: 3.082(100)(200), 3.250(66)($\bar{1}$12, 002), 2.631(44)(022), 2.854(34)($\bar{2}$02), 2.683(33)(130), 3.686(26)(021), 2.531(25)(220), 1.749(25)($\bar{3}$32, $\bar{2}$04) and 2.344(24)(131). Electron microprobe analysis gave (wt.%) MgO 20.44, CaO 26.83, P2O5 6.24, V2O5 21.09, As2O5 18.97, SO3 0.47, F 9.42, –O=F –3.97, with a total of 99.49. The empirical formula of reznitskyite, calculated on the basis of O+F = 5 atoms per formula unit, is: Ca0.97Mg1.03(V0.47As0.33P0.18S0.01)Σ0.99O3.99F1.01. Reznitskyite is a vanadate analogue of tilasite CaMg(AsO4)F and isokite CaMg(PO4)F. The mineral is named in honour of the outstanding Russian mineralogist Leonid Zinovievich Reznitsky (born 1938) who has made significant contribution to the mineralogy of vanadium.