Bortolanite, a rare mineral of the rinkite group, seidozerite supergroup occurs in two different associations in the Lovozero massif in the Kola Peninsula, Russia: (1) together with ferri-katophorite and phlogopite, it forms porous or mesh aggregates (symplectitic accretions) with euhedral contours in the contact zone of a volcano–sedimentary xenolith and eudialyte lujavrite at Kuamdespakhk Mt and (2) in intergrowths with titanite and fluorcaphite in the poikilitic feldspathoid syenites at Sengischorr Mt. In both cases, bortolanite was found in association with rosenbuschite that is close to it in chemical composition, but unlike bortolanite, it contains no REEs. The mineral is triclinic, space group P$\bar{1}$, a = 9.5807(5), b = 5.6943(4), c = 7.2813(4) Å, α = 89.891(5)°, β = 100.959(4)°, γ = 101.241(5)°, V = 382.25(4) Å3 and Z = 1.

The Lovozero bortolanite differs from the Brazilian holotype sample from de Caldas alkaline massif, Minas Gerais, due to the presence of (OH)-groups in its composition, which is indicated by Raman data. A combination of single-crystal X-ray diffraction data and electron microprobe data provides the following crystal-chemical formula: (Ca1.97Ce0.01Nd0.01Th0.01)Σ2(Ca1.39Zr0.61)Σ2(Na0.72Ca0.28)Σ1(Na1.36Ca0.56Mn0.03Zn0.01)Σ1.96(Ti0.78Zr0.08Nb0.05Mg0.05Fe0.04)Σ1Si4O14((OH)0.92O0.87F0.21)Σ2F2.

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.

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 crystal structure of nikmelnikovite, Ca12Fe2+Fe3+3Al3(SiO4)6(OH)20, a new member of the garnet supergroup from Kovdor massif, Kola Peninsula, Russia (R$\bar{3}$, a = 17.2072(6), c = 10.5689(4) Å, V = 2710.1(2) Å3 and Z = 3) has been refined to R1 = 0.046 on the basis of 1184 unique observed reflections. Nikmelnikovite is the first mineral species in the garnet supergroup that has a trigonal (rhombohedral) symmetry. The relationship between its unit cell and the pseudocubic (ideal garnet) unit cell can be described by the transformation matrix [1$\bar{1}$0 | 01$\bar{1}$ | ½½½]. The crystal-chemical relations between the ideal Ia$\bar{3}$d garnet and the nikmelnikovite structure type can be described by the following series of imaginary modifications: (1) the symmetry is lowered according to the Ia$\bar{3}$d → R$\bar{3}$ group–subgroup relationship; (2) the cation sites are split according to the following sequences: X → {X1, X2}; Y → {Y1, Y2, Y3, Y4}; Z → {Z1, Z2}; (3) the X sites remain fully occupied by Ca; (4) each Y site is occupied predominantly by a distinct chemical species: Y1 → Al (Al site), Y2 → Fe2+ (Fe1 site), Y3 → Fe3+ (Fe2 site), Y4 → vacancy (Mn site); (5) one of the Z sites (Z1) is occupied by Si, whereas the other site (Z2) is predominantly vacant. The crystal-chemical formula that takes into account the transition between the archetype and the nikmelnikovite structure type can be described as X{Ca12}Y[Fe2+Al4Fe3+2□]Z(Si6□6)O24(OH)20□4. The structural complexity of nikmelnikovite (4.529 bit/atom and 434.431 bit/cell, after H-correction) is higher than those for andradite, grossular and katoite, which is typical for low-temperature minerals formed after primary minerals with simpler structures.

The Khibiny Educational and Scientific Station (KESS) of the Faculty of Geography, M.V. Lomonosov Moscow State University (MSU), was founded in 1948. It is one of the oldest stations of the MSU Faculty of Geography and the only one located north of the Arctic Circle. It is also one of the oldest continuously operating arctic field stations in the world. For more than 70 years, the research station has fostered scientific and international collaboration. Science and education carried out at the station have always gone hand in hand and the research results have been both theoretical and practical. Many generations of Russian geographers owe their successful careers to the research activities at the Khibiny station. Nowadays, it is one of the two major student training bases for the Faculty of Geography as well as a focal point of many national and international research projects, including the International Network for Terrestrial Research and Monitoring in the Arctic (INTERACT) network.

Panskyite, Pd9Ag2Pb2S4, is a new mineral (IMA2020–039) discovered in the platinum-group element mineralisation of the Southern Kievey ore occurrence of the Fedorova–Pana layered intrusion, Kola Peninsula, Russia. It forms tiny anhedral grains (of 0.5 to 10 μm in size) in the interstices of rock-forming silicates, often forming tiny inclusions in base-metal sulfides (millerite, chalcopyrite, bornite and chalcocite) and complex intergrowths with other platinum group minerals (zvyagintsevite, laflammeite, vysotskite, thalhammerite, unnamed phase Pd9Ag2(Tl,Pb)2S4 and others). In plane-polarised light, panskyite is creamy white with weak bireflectance, weak pleochroism and distinct anisotropy with brown to grey rotation tints; it exhibits no internal reflections. Reflectance values for panskyite in air (R1, R2 in %) are: 43.8, 44.1 at 470 nm; 44.4, 44.7 at 546 nm; 45.6, 45.8 at 589 nm; and 47.2, 47.2 at 650 nm. Twelve electron-microprobe analyses of panskyite gave an average composition: Pd 55.61, Ag 12.36, Pb 23.50, Fe 0.21, Ni 0.24 and S 7.17 total 99.09 wt.%, corresponding to the formula (Pd9.05Fe0.07Ni0.07)Σ9.19Ag1.98Pb1.96S3.87 based on 17 atoms; the average of nine analyses on the synthetic analogue is: Pd 57.02, Ag 14.17, Pb 21.81 and S 7.44, total 100.44 wt.%, corresponding to Pd9.07Ag2.22Pb1.78S3.93. The density, calculated on the basis of the empirical formula, is 9.81 g/cm3. The mineral is tetragonal, space group I4/mmm, with a = 7.973(3), c = 9.139(3) Å, V = 581.0(4) Å3 and Z = 2. The crystal structure was solved from the single-crystal and powder X-ray diffraction data of synthetic Pd9Ag2Pb2S4. Panskyite is isostructural with thalhammerite (Pd9Ag2Bi2S4). The mineral name is for the locality, the Pansky massif of the Fedorova–Pana layered intrusion in the Kola Peninsula, Russia.

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.

Mitrofanovite, Pt3Te4, is a new telluride discovered in low-sulfide disseminated ore in the East Chuarvy deposit, Fedorovo–Pana intrusion, Kola Peninsula, Russia. It forms anhedral grains (up to ~20 μm × 50 μm) commonly in intergrowths with moncheite in aggregates with lukkulaisvaaraite, kotulskite, vysotskite, braggite, keithconnite, rustenburgite and Pt–Fe alloys hosted by a chalcopyrite–pentlandite–pyrrhotite matrix. Associated silicates are: orthopyroxene, augite, olivine, amphiboles and plagioclase. Mitrofanovite is brittle; it has a metallic lustre and a grey streak. Mitrofanovite has a good cleavage, along {001}. In plane-polarised light, mitrofanovite is bright white with medium to strong bireflectance, slight pleochroism, and strong anisotropy on non-basal sections with greyish brown rotation tints; it exhibits no internal reflections. Reflectance values for the synthetic analogue of mitrofanovite in air (Ro, Re’ in %) are: 58.4, 54.6 at 470 nm; 62.7, 58.0 at 546 nm; 63.4, 59.1 at 589 nm; and 63.6, 59.5 at 650 nm. Fifteen electron-microprobe analyses of mitrofanovite gave an average composition: Pt 52.08, Pd 0.19, Te 47.08 and Bi 0.91, total 100.27 wt.%, corresponding to the formula (Pt2.91Pd0.02)Σ2.93(Te4.02Bi0.05)Σ4.07 based on 7 atoms; the average of eleven analyses on synthetic analogue is: Pt 52.57 and Te 47.45, total 100.02 wt.%, corresponding to Pt2.94Te4.06. The density, calculated on the basis of the formula, is 11.18 g/cm3. The mineral is trigonal, space group R$\overline 3 $m, with a = 3.9874(1), c = 35.361(1) Å, V = 486.91(2) Å3 and Z = 3. The crystal structure was solved and refined from the powder X-ray-diffraction data of synthetic Pt3Te4. Mitrofanovite is structurally and chemically related to moncheite (PtTe2). The strongest lines in the powder X-ray diffraction pattern of synthetic mitrofanovite [d in Å (I) (hkl)] are: 11.790(23)(003), 5.891(100)(006), 2.851(26)(107), 2.137(16)(1013), 2.039(18)(0114), 1.574(24)(0120), 1.3098(21)(0027). The structural identity of natural mitrofanovite with synthetic Pt3Te4 was confirmed by electron backscatter diffraction measurements on the natural sample. The mineral name is chosen to honour Felix P. Mitrofanov, a Russian geologist who was among the first to discover platinum-group element mineralisation in the Fedorova–Pana complex.

Kihlmanite-(Ce), Ce2TiO2[SiO4](HCO3)2(H2O), is a new rare-earth titanosilicate carbonate, closely related to tundrite-(Ce). It is triclinic, P, a = 4.994(2), b = 7.54(2), c = 15.48(4) Å, α = 103.5(4), β = 90.7(2), γ = 109.2(2)o , V = 533(1) Å3, Z = 2 (from powder diffraction data) or a = 5.009(5), b = 7.533(5), c = 15.407(5) Å, α = 103.061(5), β = 91.006(5), γ = 109.285(5)°, V = 531.8(7) Å3, Z = 2 (from single-crystal X-ray diffraction data). The mineral was found in the arfvedsonite-aegirine-microcline vein in fenitized metavolcanic rock at the foot of the Mt Kihlman (Chil’man), near the western contact of the Devonian Khibiny alkaline massif and the Proterozoic Imandra-Varzuga greenstone belt. It forms brown spherulites (up to 2 cm diameter) and sheaf-like aggregates of prismatic crystals, flattened on {010} and up to 0.5 mm diameter. Both spherulites and aggregates occur in interstices in arfvedsonite and microcline, in intimate association with golden-green tundrite-(Ce). Kihlmanite-(Ce) is brown, with a vitreous lustre and a pale yellowish-brown streak. The cleavage is perfect on {010}, parting is perpendicular to c and the fracture is stepped. Mohs hardness is ∼3. In transmitted light, the mineral is yellowish brown; pleochroism and dispersion were not observed. Kihlmanite-(Ce) is biaxial (+), α = 1.708(5), β = 1.76(1), γ = 1.82(1) (589 nm), 2Vcalc = 89°. The optical orientation is Y ^ c = 5°, other details are unclear. The calculated and measured densities are 3.694 and 3.66(2) g cm−3, respectively. The mean chemical composition, determined by electron microprobe, is: Na2O 0.13, Al2O3 0.24, SiO2 9.91, CaO 1.50, TiO2 11.04, MnO 0.26, Fe2O3 0.05, Nb2O5 2.79, La2O3 12.95, Ce2O3 27.33, Pr2O3 2.45, Nd2O3 8.12, Sm2O3 1.67, Gd2O3 0.49 wt.%, with CO2 15.0 and H2O 6.0 wt.% (determined by wet chemical and Penfield methods, respectively), giving a total of 99.93 wt.%. The empirical formula calculated on the basis of Si + Al = 1 atom per formula unit is (Ca0.16Na0.11Mn0.02)∑0.29[(Ce0.98La0.47Pr0.09Nd0.29Sm0.06Gd0.02)∑1.91(Ti0.82Nb0.12)∑0.94O2 (Si0.97Al0.03)∑1O4.02(HCO3)2.01](H2O)0.96. The simplified formula is Ce2TiO2(SiO4)(HCO3)2·H2O. The mineral reacts slowly in cold 10% HCl with weak effervescence and fragmentation into separate plates. The strongest X-ray powder-diffraction lines [listed as d in Å(I) (hkl)] are as follows: 15.11(100)(00), 7.508(20)(00), 6.912(12)(01), 4.993(14)(00), 3.563(15)(01), 2.896(15)(1). The crystal structure of kihlmanite-(Ce) was refined to R1 = 0.069 on the basis of 2441 unique observed reflections (MoKα, 293 K). It is closely related to the crystal structure of tundrite-(Ce) and is based upon [Ce2TiO2(SiO4)(HCO3)2] layers parallel to (001). Kihlmanite-(Ce) can be considered as a cationdeficient analogue of tundrite-(Ce). The mineral is named in honour of Alfred Oswald Kihlman (1858–1938), a remarkable Finnish geographer and botanist who participated in the Wilhelm Ramsay expeditions to the Khibiny Mountains in 1891–1892. The mineral name also reflects its occurrence at the Kihlman (Chil’man) Mountain.

Apatite-dolomite carbonatite at Lesnaya Varaka, Kola Peninsula, Russia, hosts intricate mineral intergrowths composed of lueshite in the core and pyrochlore-group minerals in the rim. Lueshite is a primary Nb-bearing phase in the carbonatite and ranges in composition from cerian lueshite to almost pure NaNbO3. For comparison, the compositional variation of lueshite from the Kovdor and Sallanlatvi carbonatites is described. At Lesnaya Varaka, lueshite is replaced by nearly stoichiometric Na-Ca pyrochlore due to late-stage re-equilibration in the carbonatite system. X-ray powder diffraction data for both minerals are presented. Barian strontiopyrochlore, occurring as replacement mantles on Na-Ca pyrochlore, contains up to 43% Sr and 8–18% Ba at the A-site, and shows a high degree of hydration and strong ionic deficiency at the A- and Y-sites. This mineral is metamict and, upon heating, recrystallises to an aeschynite-type structure. Monazite-(Ce) found as minute crystals in fractures, represents the solid solution between monazite-(Ce) CePO4, brabantite CaTh(PO4)2 and SrTh(PO4)2. Our data indicate the high capacity of the monazite structure for Th and accompanying divalent cations at low temperatures and pressures that has a direct relevance to solving the problem of long-term conservation of radioactive wastes. Monazite-(Ce) and barian strontiopyrochlore are products of low-temperature hydrothermal or secondary (hypergene) alteration of the primary mineral assemblage of the carbonatite.

Three new valleriite-group minerals, ekplexite (Nb,Mo)S2·(Mg1−xAlx)(OH)2+x, kaskasite (Mo,Nb)S2·(Mg1−xAlx)(OH)2+x and manganokaskasite (Mo,Nb)S2·(Mn1−xAlx)(OH)2+x are found at Mt Kaskasnyunchorr, Khibiny alkaline complex, Kola Peninsula, Russia. They occur in fenite consisting of orthoclase−anorthoclase and nepheline with fluorophlogopite, corundum, pyrrhotite, pyrite, rutile, monazite-(Ce), graphite, edgarite, molybdenite, tungstenite, alabandite, etc. Ekplexite forms lenticular nests up to 0.2 mm × 1 mm × 1 mm consisting of near-parallel, radiating or chaotic aggregates of flakes. Kaskasite and manganokaskasite mainly occur as flakes and their near-parallel ‘stacks’ (kaskasite: up to 0.03 mm × 1 mm × 1.5 mm; manganokaskasite: up to 0.02 mm × 0.5 mm × 1 mm) epitaxially overgrow Ti-bearing pyrrhotite partially replaced by Ti-bearing pyrite. All three new minerals are opaque, ironblack, with metallic lustre. Cleavage is {001} perfect and mica-like. Flakes are very soft, flexible and inelastic. Mohs hardness is ∼1. D(calc.) = 3.63 (ekplexite), 3.83 (kaskasite) and 4.09 (manganokaskasite) g cm−3. In reflected light all these minerals are grey, without internal reflections. Anisotropism and bireflectance are very strong and pleochroism is strong. The presence of OH groups and an absence of H2O molecules are confirmed by the Raman spectroscopy data. Chemical data (wt.%, electron probe) for ekplexite, kaskasite and manganokaskasite, respectively, are: Mg 6.25, 5.94, 0.06; Al 4.31, 3.67, 3.00; Ca 0.00, 0.04, 0.00; V 0.86, 0.16, 0.15; Mn 0.00, 0.23, 11.44; Fe 0.44, 1.44, 2.06; Nb 18.17, 13.39, 14.15; Mo 15.89, 23.18, 20.08; W 8.13, 7.59, 9.12; S 27.68, 27.09, 24.84; O 16.33, 15.66, 13.36; H (calc.) 1.03, 0.99, 0.89; total 99.09, 99.08, 99.15. The empirical formulae calculated on the basis of 2 S a.p.f.u. are: ekplexite: (Nb0.45Mo0.38W0.10V0.04)S0.97S2· (Mg0.60Al0.37Fe0.02)S0.99(OH)2.36; kaskasite: (Mo0.57Nb0.34W0.10V0.01)S1.02S2· (Mg0.58Al0.32Fe0.06Mn0.01)S0.97(OH)2.32; manganokaskasite: (Mo0.54Nb0.39W0.13V0.01)S1.07S2· (Mn0.54Al0.29Fe0.10Mg0.01)S0.94(OH)2.28. All three minerals are trigonal, space groups Pm1, P3m1 or P321, one-layer polytypes (Z = 1). Their structures are non-commensurate and consist of the MeS2-type (Me = Nb, Mo, W) sulfide modules and the brucite-type hydroxide modules. Parameters of the sulfide (main) sub-lattices (a, c in Å, V in Å3) are: 3.262(2), 11.44(2), 105.4(4) (ekplexite); 3.220(2), 11.47(2), 102.8(4) (kaskasite); 3.243(3), 11.61(1), 105.8(3) (manganokaskasite). Parameters of the hydroxide sub-lattices (a, c in Å, V in Å3) are: 3.066(2), 11.52(2), 93.8(4) (ekplexite); 3.073(2), 11.50(2), 94.0(4) (kaskasite); 3.118(3), 11.62(1), 97.9(2) (manganokaskasite). Ekplexite was named from the Greek word έκπληξη meaning surprise, for its exotic combination of major chemical constituents, kaskasite after the discovery locality and manganokaskasite as a Mn analogue of kaskasite.

Holtite, approximately (Al,Ta,□)Al6(BO3)(Si,Sb3+,As3+)Σ3O12(O,OH,□s)Σ3, is a member of the dumortierite group that has been found in pegmatite, or alluvial deposits derived from pegmatite, at three localities: Greenbushes, Western Australia; Voron'i Tundry, Kola Peninsula, Russia; and Szklary. Lower Silesia, Poland. Holtite can contain >30 wt.% Sb2O3, As2O3, Ta2O5, Nb2O5, and TiO2 (taken together), but none of these constituents is dominant at a crystallographic site, which raises the question whether this mineral is distinct from dumortierite. The crystal structures of four samples from the three localities have been refined to R1 = 0.02—0.05. The results show dominantly: Al, Ta, and vacancies at the Al(l) position; Al and vacancies at the Al(2), (3) and (4) sites; Si and vacancies at the Si positions; and Sb, As and vacancies at the Sb sites for both Sb-poor (holtite I) and Sb-rich (holtite II) specimens. Although charge-balance calculations based on our single-crystal structure refinements suggest that essentially no water is present, Fourier transform infrared spectra confirm that some OH is present in the three samples that could be measured. By analogy with dumortierite, the largest peak at 3505-3490 cm-1 is identified with OH at the O(2) and O(7) positions. The single-crystal X-ray refinements and FTIR results suggest the following general formula for holtite: Al7-[5x+y+z]/3 (Ta,Nb)x□[2x+y+z]\3,BSi3-y(Sb,As)yO18-y-z(OH)z, where x is the total number of pentavalent cations, y is the total amount of Sb + As, and z ⩽ y is the total amount of OH. Comparison with the electron microprobe compositions suggests the following approximate general formulae Al5.83(Ta,Nb)0.50□0.67BSi2.50(Sb,As)0.50O17.00(OH)0.50 and Al5.92(Ta,Nb)0.25□0.83BSi2.00(Sb,As)1.00O16.00(OH)1.00 for holtite I and holtite II respectively. However, the crystal structure refinements do not indicate a fundamental difference in cation ordering that might serve as a criterion for recognizing the two holtites as distinct species, and anion compositions are also not sufficiently different. Moreover, available analyses suggest the possibility of a continuum in the Si/(Sb + As) ratio between holtite I and dumortierite, and at least a partial continuum between holtite I and holtite II. We recommend that use of the terms holtite I and holtite II be discontinued.

Zirkelite, a cubic mineral of general formula (Ti,Ca,Zr)O2−x occurs as an accessory mineral in phoscorites, carbonatites and associated rocks in the Sebl'yavr complex. After pyrochlore, it is the main mineral concentrating niobium in these rocks. Zirkelite forms platy crystals comprising polysynthetic octahedral twins, often having a complex skeletal internal structure within a cuboctahedral external morphology. The mineral is largely metamict, but after heating to 800°C it produces a cubic crystalline structure with ao = 5.157 ±0.006 Å. It is black to brownish-black in colour, VHN = 760−780 kg.mm−2, density = 4.27 g.cm−3, and reflectance = 12.5%.

Chemically, zirkelite is relatively enriched in Nb2O5 (up to 14.5 wt.%) and ThO2 (up to 7.7 wt.%), and it displays four compositionally-distinct zones which probably formed during primary crystallisation processes. It is patchily altered where it is associated with an unidentified Ba, Ti, Nb, Zr silicate phase which partly replaces and pseudomorphs it. Under the current IMA-approved nomenclature scheme, non-crystalline (metamict) minerals of the composition described here would normally be given the general species name zirconolite, with the name zirkelite confined to the cubic mineral. However, at Sebl'yavr, the name zirkelite is used because the mineral displays a well-defined cubic crystal morphology and has a cubic structure after heating.

The compositions and textural relationships of the oxide minerals zirconolite, pyrochlore and baddeleyite are described. These occur as accessory minerals, often intergrown with each other, from a phoscorite rock associated with the Kovdor carbonatite complex. Both the zirconolite and baddeleyite have relatively high concentrations of Nb and Ta; the pyrochlore is rich in U and Ta. Backscattered electron images, coupled with detailed microprobe analyses, reveal complex compositional zoning in zirconolite and pyrochlore which reflect changes in the fluid composition during growth of these minerals. A comparison is made of incompatible element ratios Zr/Hf, Nb/Ta and Th/U between the three accessory minerals.

The Turiy Massif, on the southern coast of the Kola Peninsula, consists of five intrusive complexes containing a variety of carbonatites, phoscorites, melilitolites, ijolites and pyroxenites. Petrographic and mineralogical studies of the different rocks show that the samples are texturally heterogeneous. Minerals including apatite, garnet, magnetite, melilite, mica and pyroxene, show systematic variations in composition relating to the rock type in which they occur. Compositional similarities and/or distinct trends are seen in the mineral compositions within the each of the pyroxenite-melilitolite, and melteigite-ijolite rock series, indicating linked petrogenetic histories within each of the two series. The carbonatites from the northern complex may be related to nearby melilitolites, but the central complex carbonatites and phosocorites do not bear any mineralogical (or isotopic) similarities to any of the silicate rocks within the massif.

Kazanskyite, Ba & TiNbNa3Ti(Si2O7)2O2(OH)2(H2O)4, is a Group-III TS-block mineral from the Kirovskii mine, Mount Kukisvumchorr, Khibiny alkaline massif, Kola Peninsula, Russia. The mineral occurs as flexible and commonly bent flakes 2–15 μm thick and up to 330 μm across. It is colourless to pale tan, with a white streak and a vitreous lustre. The mineral formed in a pegmatite as a result of hydrothermal activity. Associated minerals are natrolite, barytolamprophyllite, nechelyustovite, hydroxylapatite, belovite-(La), belovite-(Ce), gaidonnayite, nenadkevichite, epididymite, apophyllite-(KF) and sphalerite. Kazanskyite has perfect cleavage on {001}, splintery fracture and a Mohs hardness of 3. Its calculated density is 2.930 g cm–3. Kazanskyite is biaxial positive with α 1.695, β 1.703, γ 1.733 (λ590 nm), 2Vmeas = 64.8(7)°, 2Vcalc = 55.4°, with no discernible dispersion. It is not pleochroic. Kazanskyite is triclinic, space group P, a 5.4260(9), b 7.135(1), c 25.514(4) Å, α 90.172(4), β 90.916(4), γ 89.964(3)°, V 977.61(3) Å3. The strongest lines in the X-ray powder-diffraction pattern [d(Å)(I)(hkl)] are: 2.813(100)(12,1), 2.149(82)(22,20,207,220,22), 3.938(70)(13,112), 4.288(44)(11,10,110,11), 2.128(44)(22,2,14,221,14,221,23), 3.127(39)(16,115), 3.690(36)(14), 2.895(33)(13,121) and 2.955(32)(10,120,12). Chemical analysis by electron microprobe gave Nb2O59.70, TiO219.41, SiO228.21, Al2O30.13, FeO 0.28, MnO 4.65, BaO 12.50, SrO 3.41, CaO 0.89, K2O 1.12, Na2O 9.15, H2O 9.87, F 1.29, O = F –0.54, sum 100.07 wt.%; H2O was determined from structure refinement. The empirical formula is (Na2.55Mn0.31Ca0.11Fe2+0.03)Σ3(Ba0.70Sr0.28K0.21Ca0.03)Σ1.22(Ti2.09Nb0.63Mn0.26Al0.02)Σ3Si4.05O21.42H9.45F0.59, calculated on 22 (O + F) a.p.f.u., Z = 2. The structural formula of the form AP2MH2MO4(Si2O7)2XO4XPMXPA(H2O)n is (Ba0.56Sr0.22K0.15Ca0.03☐0.04)Σ1(☐0.74Ba0.14Sr0.06K0.06)Σ1(Ti0.98Al0.0 2)Σ1(Nb0.63Ti0.37)Σ1(Na2.55Mn0.31Ca0.11Fe2+0.03)Σ3(Ti0.74Mn0.26)Σ1(Si2O7)2O2(OH1.41F0.59)Σ2(H2O)(☐0.74H2O0.26)Σ1(H2O)2.74. Simplified and ideal formulae are as follows: Ba(☐,Ba)Ti(Nb,Ti)(Na,Mn)3(Ti,Mn)(Si2O7)2O2(OH,F)2(H2O)4 and Ba☐TiNbNa3Ti(Si2O7)2O2(OH)2(H2O)4. The Raman spectrum of the mineral contains the following bands: 3462 cm–1 (broad) and 3545 and 3628 cm–1 (sharp). The crystal structure was solved by direct methods and refined to an R1 index of 8.09%. The crystal structure of kazanskyite is a combination of a TS (titanium silicate) block and an I (intermediate) block. The TS block consists of HOH sheets (H is heteropolyhedral and O is octahedral). The TS block exhibits linkage and stereochemistry typical for Group-III (Ti = 3 a.p.f.u.) Ti-disilicate minerals. The TS block has two different H sheets where (Si2O7) groups link to [5]-coordinated Ti and [6]-coordinated Nb polyhedra, respectively. There are two peripheral sites, AP(1,2), occupied mainly by Ba (less Sr and K) at 96% and 26%. There are two I blocks: the I1 block is a layer of Ba atoms; the I2 block consists of H2O groups and AP(2) atoms. The TS and I blocks are topologically identical to those in the nechelyustovite structure. The mineral is named in honour of Professor Vadim Ivanovich Kazansky, a prominent Russian ore geologist and an expert in Precambrian metallogeny.

This study presents a complete characterization of kenoplumbomicrolite, (Pb,□)2Ta2O6[□,(OH),O], occurring in an amazonite pegmatite from Ploskaya Mountain, Western Keivy Massif, Kola Peninsula, Murmanskaja Oblast, Northern Region, Russia.

Kenoplumbomicrolite occurs in yellowish brown octahedral, cuboctahedral and massive crystals, up to 20 cm, has a white streak, a greasy lustre and is translucent. The Mohs hardness is ~6. Attempts to measure density (7.310–7.832 g/cm3) were affected by the ubiquitous presence of uraninite inclusions. Reflectance values were measured in air and immersed in oil. Kenoplumbocrolite is optically isotropic. The empirical formula is (Pb1.30□0.30Ca0.29Na0.08U0.03)Σ2.00(Ta0.82Nb0.62Si0.23Sn4+0.15Ti0.07Fe3+0.10Al0.01)Σ2.00O6[□0.52(OH)0.25O0.23]Σ1.00 (from the crystal used for the structural study) and (Pb1.33□0.66Mn0.01)Σ2.00(Ta0.87Nb0.72Sn4+0.18Fe3+0.11W0.08Ti0.04)Σ2.00O6[□0.80(OH)0.10O0.10]Σ1.00 (average including additional fragments). The mineral is cubic, space group Fd$\overline 3 $m. The unit-cell parameters refined from powder X-ray diffraction data are a = 10.575(2) Å and V = 1182.6(8) Å3, which are in accord with those obtained previously from a single crystal of a = 10.571(1) Å, V = 1181.3(2) Å3 and Z = 8. The mineral description and its name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA2015-007a).