Eudialyte-related compounds have been synthesised hydrothermally at T = 600°C and P = 2 kbar from a stoichiometric mixture of Na2CO3, CaO, Fe2O3, ZrOCl2 and SiO2 using the Na:Ca:Fe:Zr:Si ratios corresponding to the eudialyte end-member Na15Ca6Fe3Zr3Si(Si25O73)(OH)Cl2⋅H2O, in the presence of 1 M aqueous solutions of NaCl and NaF. The synthesis was carried out in platinum ampoules over 10 days. Natural raslakite (a Ca-deficient member of the eudialyte group) was used as a seed and added in amounts corresponding to 2 wt.% of the whole charge. The products were characterised by powder X-ray diffraction, IR and Raman spectroscopy, morphological features, and electron probe microanalyses. In experiments with NaCl, almost pure eudialyte-type compounds were obtained. Synthesis in the presence of a NaF solution resulted in the formation of a F-dominant eudialyte-type compound related to raslakite as the main product and aegirine, vlasovite and lalondeite as by-products. All synthesised eudialyte-type compounds are Zr-rich and Fe-deficient, similar to eudialyte-group minerals from hyperagpaitic rocks related to foyaites. The increased NaCl contents in the reaction system results in increased Ca content in the synthesised eudialyte-related compounds. The crystal-chemical formulae of the synthesised eudialyte-type compounds are derived based on general regularities established earlier for eudialyte-group minerals.

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 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 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.

A rare earth element (REE)-, Cr- and Mg-bearing variety of the vanadium epidote-group mineral mukhinite occurs in a calcite–dolomite carbonatite dyke cutting metamorphosed volcano-sedimentary rocks exposed in the walls of the quarry of the Svetlinsky gold deposit, South Urals. This mineral was found in a paragene assemblage including native sulphur, phlogopite and fluorophlogopite, together with accessory pyrite, other sulfides and sulfosalts, gold, Cr- and V-bearing muscovite, margarite, Cr- and V-bearing dravite, fluoro-tremolite, actinolite, fluoro-pargasite, anhydrite, apatite, uranium hydroxides, V-rich titanite, V- and Nb-rich rutile, spinel and corundum. The contents of ΣREE2O3 and V2O3 in mukhinite vary in the ranges of 4.01–9.69 and 5.34–7.46 wt.%, respectively. A Raman spectrum of REE-rich mukhinite is provided. The main schemes of isomorphic substitutions in mukhinite are ΣREE + Mg ↔ Ca + Al and V+Cr ↔ Al. The crystal structure of REE-rich mukhinite has been studied by single-crystal X-ray diffraction analysis. The mineral is monoclinic, with the space group P21/m, and unit-cell parameters are: a = 8.8972(11) Å, b = 5.6221(6) Å, c = 10.1519(12) Å, β = 115.169° and V = 459.60(11) Å3. The crystal structure of REE-rich mukhinite is similar to that of its synthetic analogue; the refined crystal-chemical formula of the sample studied is (Z = 2): {A1CaA2(Ca0.8REE0.2)}{M1(Al0.95Cr0.05)M2AlM3[(V,Cr)3+0.40Al0.35Mg0.25]}(Si2O7)(SiO4)O(OH).

Zolotarevite (IMA2020-076), ideally Na5Zr[Si6O15(ОН)3]⋅2–3H2O, is а new mineral of the lovozerite group. The mineral was found in a leucocratic nepheline syenite from Kedykverpakhk Mt., Lovozero alkaline massif, Kola Peninsula, Russia. It occurs as anhedral grains up to 1 mm across and is associated with microcline–perthite, nepheline, sodalite, aegirine, lamprophyllite, lueshite, umbozerite, lomonosovite, nastrophite, a mineral of the kazakovite–tisinalite series, sphalerite and löllingite. Zolotarevite is cherry red, with a vitreous lustre and white streak. The mineral is brittle, with a Mohs hardness of 5. Cleavage was not observed; the fracture is uneven. The measured density is 2.75(5) g⋅cm–3, the density calculated using the empirical formula and single-crystal unit-cell parameters is 2.85 g⋅cm–3. Zolotarevite is anomalously biaxial (–), α = 1.580(2), β = 1.600(2) and γ = 1.602(2) (for λ = 589 nm); 2Vmeas < 10°. Chemical data (electron microprobe, wt.%) are: Na2O 20.41, СаО 0.42, MnO 3.49, Fе2O3 0.55, SiO2 52.46, ТiO2 1.34, ZrO2 11.33, H2O (calculated from the structural formula) 10.20, total 100.20. The empirical formula based оn 6 Si atoms per formula unit is Na4.53Zr0.63Mn0.34Ti0.11Ca0.05Fe3+0.05Si6O14.43(ОН)3.56(H2О)2.11. Zolotarevite is trigonal, space group R${\bar 3}$m, with a = 10.294(6) Å, c = 13.115(8) Å, V = 1203.7(16) Å3 and Z = 3. The crystal structure was solved from single-crystal data and refined to R1 = 0.049. The strongest lines of the powder X-ray diffraction pattern [d in Å (I) (hkl)] are: 7.37 (69) (101); 5.26 (56) (012); 3.686 (64) (202); 3.330 (79) (113); 3.265 (99) (211), 2.640 (100) (024) and 2.576 (60) (220). Zolotarevite is unique in that it is a highly hydrated lovozerite-group mineral with the B site occupied by variable amounts of H2O.

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 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 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).

An unusual highly hydrated and Na-depleted variety of elpidite was identified in a hydrothermally altered peralkaline pegmatite at Mt. Yukspor in the Khibiny alkaline complex, Kola Peninsula, Russia. It differs from ‘ordinary’ elpidite, ideally Na2ZrSi6O15⋅3H2O, in its crystal chemical features, infrared spectrum and optical characteristics. The chemical composition (wt.%, electron microprobe, H2O by TGA) is: Na2O 5.45, K2O 0.67, CaO 0.05, SiO2 60.32, TiO2 1.34, ZrO2 18.43, Nb2O5 0.65, H2O 12.80, total 99.71. The empirical formula calculated on the basis of 6 Si and 15 O atoms is [(Na1.05K0.08Ca0.01)Σ1.14(H3O)0.74]Σ1.88(Zr0.89Ti0.10Nb0.03)Σ1.02Si6O15⋅3.47H2O; the H2O:H3O ratio was calculated from the charge balance requirement, taking into account the results of crystal structure refinement. The highly hydrated variety of elpidite is orthorhombic, Pma2, a = 14.5916(6), b = 7.3294(3), c = 7.1387(2) Å, V = 763.47(5) Å3 and Z = 2. The crystal structure was solved from single-crystal X-ray diffraction data, R1 = 3.43%. The structure is based upon an elpidite-type heteropolyhedral Zr–Si–O framework with Na+ and H3O+ cations and H2O molecules in the zeolitic channels. Hydronium cations substitute for water molecules in one of the extra-framework sites. This variety of elpidite could be considered as an intermediate product of natural ion-exchange reaction between ‘ordinary’ elpidite and a low-temperature hydrothermal fluid.

The new triazolate mineral bojarite (IMA2020-037), Cu3(N3C2H2)3(OH)Cl2⋅6H2O, is found in a guano deposit located at the Pabellón de Pica Mountain, Iquique Province, Tarapacá Region, Chile. Associated minerals are salammoniac, halite, nitratine and belloite. Bojarite occurs as blue fine-grained porous aggregates up to 1 mm × 3 mm × 5 mm combined typically in interrupted earthy crusts. The mineral is brittle. The Mohs hardness is 2. Dcalc = 2.057 g cm–3. The IR and Raman spectra show the presence of the 1,2,4-triazolate anion and H2O molecules. Bojarite is optically isotropic and n = 1.635(2) (λ = 589 nm). The chemical composition (electron-microprobe data for Na, Mg, Fe, Cu and Cl; H, C and N contents measured by gas chromatography on products of ignition at 1200°C; wt.%) is: Na 0.22, Mg 0.74, Fe 0.99, Cu 29.73, Cl 13.62, N 20.4, C 11.6, H 3.3, O (calculated by stoichiometry) 19.93, total 100.53.

The empirical formula is (Cu2.68Mg0.17Fe0.10Na0.05)Σ3(N3C2H2)2.755[(OH)][Cl2.19(H2O)3.77(OH)0.04]Σ6⋅2.3H2O. The idealised formula is Cu3(N3C2H2)3(OH)Cl2⋅6H2O. The crystal structure of bojarite was refined based on powder X-ray diffraction data, using the Rietveld method. The final agreement factors are: Rp = 0.0225, Rwp = 0.0310 and Robs = 0.0417. The new mineral is cubic, space group Fd$\bar{3}$c; a = 24.8047(5) Å, V = 15,261.6(5) Å3 and Z = 32. The strongest reflections of the powder X-ray diffraction pattern [d, Å (I,%)(hkl)] are: 8.83 (31)(220), 7.19 (100)(222), 6.23 (35)(400), 5.077 (28)(422), 4.194 (28)(531), 3.584 (23)(444), 2.865 (28)(660, 751) and 2.723 (22)(753, 842).

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.

The rhodonite-group mineral with the idealised, end-member formula MnMn4[Si5O15] and the crystal chemical formula VIIM(5)MnVIM(1–3)Mn3VIIM(4)Mn[Si5O15] (Roman numerals indicate coordination numbers) is defined as a valid mineral species named vittinkiite after the type locality Vittinki (Vittinge) mines, Isokyrö, Western and Inner Finland Region, Finland. Vittinkiite is an isostructural analogue of rhodonite, ideally CaMn4[Si5O15], with Mn2+ > Ca at the M(5) site. Besides Vittinki, vitiinkiite was found in more than a dozen rhodonite deposits worldwide, however, it is significantly less common in comparison with rhodonite. The mineral typically forms pink to light pink massive, granular aggregates and is associated with quartz, rhodonite, tephroite, pyroxmangite and Mn oxides. Vittinkiite is optically biaxial (+), with α = 1.725(4), β = 1.733(4), γ = 1.745(5) and 2Vmeas = 75(10)° (589 nm). The chemical composition of the holotype (wt.%, electron microprobe) is: MgO 0.52, CaO, 0.93, MnO 51.82, FeO 1.26, ZnO 0.11, SiO2 46.48, total 101.12. The empirical formula calculated based on 15 O apfu is Mn4.71Ca0.11Fe0.11Mg0.08Zn0.01Si4.99O15. Vittinkiite is triclinic, space group P$\bar{1}$, with a = 6.6980(3), b = 7.6203(3), c = 11.8473(5) Å, α = 105.663(3), β = 92.400(3), γ = 94.309(3)°, V = 579.38(7) Å3 and Z = 2. The crystal structure is solved on a single crystal to R1 = 3.85%. Polymorphism of MnSiO3 (rhodonite-, pyroxmangite-, garnet- and clinopyroxene-type manganese metasilicates) is discussed, as well as the relationship between vittinkiite and pyroxmangite, ideally Mn7[Si7O21], and the application of infrared spectroscopy for the identification of manganese pyroxenoids.

Two new isostructural minerals radekškodaite-(La) (CaLa5)(Al4Fe2+)[Si2O7][SiO4]5O(OH)3 and radekškodaite-(Ce) (CaCe5)(Al4Fe2+)[Si2O7][SiO4]5O(OH)3 were discovered in polymineralic nodules from the Mochalin Log REE deposit, South Urals, Russia. Radekškodaite-(La) is associated with allanite-(Ce), allanite-(La), bastnäsite-(Ce), bastnäsite-(La), ferriallanite-(Ce), ferriallanite-(La), ferriperbøeite-(La), fluorbritholite-(Ce), törnebohmite-(Ce) and törnebohmite-(La). Radekškodaite-(Ce) is associated with ancylite-(Ce), bastnäsite-(Ce), bastnäsite-(La), lanthanite-(La), perbøeite-(Ce) and törnebohmite-(Ce). The new minerals form isolated anhedral grains up to 0.35 × 0.75 mm [radekškodaite-(La)] and 1 mm × 2 mm [radekškodaite-(Ce)]. Both minerals are greenish-brown with vitreous lustre. Dcalc = 4.644 [radekškodaite-(La)] and 4.651 [radekškodaite-(Ce)] g cm–3. Both minerals are optically biaxial (+); radekškodaite-(La): α = 1.790(7), β = 1.798(5), γ = 1.825(8) and 2Vmeas = 60(10)°; radekškodaite-(Ce): α = 1.798(6), β = 1.806(6), γ = 1.833(8) and 2Vmeas = 65(10)°. Chemical data [wt.%, electron-microprobe; FeO:Fe2O3 by charge balance; H2O by stochiometry; radekškodaite-(La)/radekškodaite-(Ce)] are: CaO 3.40/2.74, La2O3 27.68/22.23, Ce2O3 20.39/24.30, Pr2O3 0.94/1.48, Nd2O3 1.71/3.18, ThO2 0.23/0.24, MgO 0.85/1.04, Al2O3 10.35/10.84, MnO 0.64/0.69, FeO 2.55/2.76, Fe2O3 3.12/2.57, TiO2 0.13/0.04, SiO2 26.03/26.10, F 0.10/0.09, H2O 1.62/1.63, –O=F –0.04/–0.04, total 99.70/99.89. The empirical formulae based on O28(OH,F)3 are: radekškodaite-(La): (Ca0.98Th0.01La2.75Ce2.01Nd0.16Pr0.09)Σ6.00(Al3.28Fe3+0.63Fe2+0.57Mg0.34Mn0.15Ti0.03)Σ5.00Si7.00O28[(OH)2.91F0.09]; radekškodaite-(Ce): (Ca0.79Mn0.16Th0.01Ce2.39La2.20Nd0.30Pr0.14)Σ5.99(Al3.43Fe2+0.62Fe3+0.52Mg0.42Ti0.01)Σ5.00Si7.00O28[(OH)2.92F0.08]. Both minerals are monoclinic, P21/m; the unit-cell parameters [radekškodaite-(La)/radekškodaite-(Ce)] are: a = 8.9604(3)/8.9702(4), b = 5.7268(2)/5.7044(2), c = 25.1128(10)/25.1642(13) Å, β = 116.627(5)/116.766(6)°, V = 1151.98(7)/1149.68(11) Å3 and Z = 2/2. The crystal structures are solved based on single-crystal X-ray diffraction data; R = 0.0554 [radekškodaite-(La)] and 0.0769 [radekškodaite-(Ce)]. Both minerals belong to the epidote–törnebohmite polysomatic series and represent first members of ET2-type: their structure consists of regular alternating modules, one slab of the epidote (E) structure and two slabs of törnebohmite (T). The rootname radekškodaite is given in honor of the Czech mineralogist Radek Škoda (born 1979), Associate Professor at Masaryk University, Brno, Czech Republic. The suffix-modifier -(La) or -(Ce) indicates the predominance of La or Ce among REE in the mineral.

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).