Abstract—Meliphanite is an abundant mineral within a large nepheline syenite pegmatite and surrounding metasomatite of the Sakharjok alkaline massif, Kola Peninsula. In the pegmatite, it occurs as euhedral crystals enriched in Al, whereas in metasomatite, it forms poikilitic crystals substantially depleted in Al with a higher OH– content. Compared to meliphanite from deposits in Norway, the Sakharjok mineral is richer in Na and contains OH groups. Leucophanite is rare in the Sakharjok massif. It is closely intergrown with meliphanite in metasomatic rocks. Its chemical composition is constant in most components (except fluorine) and its formula is close to ideal. The unique paragenesis of meliphanite and leucophanite, which was previously considered as impossible, resulted from the metasomatic origin of the minerals.

•Thermal decomposition of complex compounds in argon was investigated.•Metal-carbon compositions were obtained in the temperature range 600-900°C•Free carbon with a specific surface area up to 380 m2/g isolated from solid of thermolysis products.

The thermal decomposition was investigated for the double complex compound (DCC) [Co(en)(3)][Fe(C2O4)(3)] in an argon atmosphere at a heating rate of 5 K/min and the initial amount of complex 20-30 mmol. The composition of solid decomposition products was determined for fixed temperatures 310, 370, 430, 500, 550, 600 and 700 degrees C. It has been established that all products contain significant (about 30 % of the initial) amount of carbon. The residual carbon in the form of hollow prisms, repeating the shape of initial compound crystals, was isolated from decomposition products at >= 500 degrees C during treatment with hydrochloric acid. Isolated carbons contain an admixture of metals (up to 33 %) and are oxidized in air to CO2 at a temperature range 300-600 degrees C.

The rare beryllium silicate, meliphanite, from nepheline syenite pegmatite of the Sakharjok massif, Kola Peninsula has been studied. The chemical composition of the mineral has been refined using infrared and Raman spectroscopy; bulk chemical, thermal, and electron microprobe analyses; and singe crystal X-ray diffraction. The obtained data unambiguously support the presence of H 2 O in the mineral and refine the crystal chemical formula of meliphanite from Sakharjok: Ca 4.00 (Na 3.12 Ca 0.88 ) Σ4.00 (Be 3.60 Si 0.40 ) Σ4.00 Al 1.00 (Si 6.74 Be 0.26 ) Σ7.00 O 24.00 [F 3.33 (OH) 0.51 O 0.16 ] Σ4.00 .

Nikmelnikovite, Ca12Fe2+Fe\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_{3}^{{3 + }}$$\end{document}Al3(SiO4)6(OH)20, a new mineral from the Kovdor massif (Kola Peninsula, Russia), is described. It is the first trigonal representative of the garnet supergroup. The mineral is named in honor of Academician Nikolai Nikolaevich Melnikov (1938–2018), an outstanding Soviet and Russia mining engineer, long-time (1981–2015) director of the Mining Institute of the Kola Science Center, Russian Academy of Sciences.

Приведено описание никмельниковита Ca 12 Fe 2+ Fe 3 3+ Al 3 (SiO 4 ) 6 (OH) 20 - нового минерала из Ковдорского массива (Кольский полуостров, Россия) и первого тригонального представителя надгруппы граната. Минерал назван в честь академика Николая Николаевича Мельникова (1938-2018), выдающегося советского и российского горного инженера, директора Горного института Кольского научного центра РАН (1981-2015).

Nikmelnikovite, Ca12Fe2+Fe3+3Al3(SiO4)6(OH)20, is a new mineral from the Kovdor massif, Kola peninsula, Russian Federation. It is the first trigonal member of the garnet supergroup. The mineral is named in honor of Academician Nikolay Nikolaevich Melnikov (1938-2018), an outstanding Soviet and Russian mining engineer, long-time (1981-2015) director of the Mining Institute of the Kola Science Center, Russian Academy of Sciences.

Nikmelnikovite, Ca 12 Fe 2+ Fe _3^3 + Al 3 (SiO 4 ) 6 (OH) 20 , a new mineral from the Kovdor massif (Kola Peninsula, Russia), is described. It is the first trigonal representative of the garnet supergroup. The mineral is named in honor of Academician Nikolai Nikolaevich Melnikov (1938–2018), an outstanding Soviet and Russia mining engineer, long-time (1981–2015) director of the Mining Institute of the Kola Science Center, Russian Academy of Sciences.

A process has been developed for preparing boron-doped niobium pentoxides Nb 2 O 5 〈B〉 to be used as precursors in the sysnthesis of nithium biobate batches LiNbO 3 〈B〉 having tailored dopant concentrations. Solutions of various origins were used to isolate Nb 2 O 5 〈B〉. A method has been advanced to account for boron loss as volatile compounds upon the heat treatment of niobium hydroxide in order to determine the boron amount to be added to niobium hydroxide in the form of H 3 BO 3 . The boron concentration in LiNbO 3 〈B〉 during lithium niobate synthesis is shown to be independent of the origin of the Nb 2 O 5 〈B〉 precursor with the same as-batch boron concentration. The phase compositions of Nb 2 O 5 〈B〉 and LiNbO 3 〈B〉 have been characterized by X-ray powder diffraction and IR spectroscopy and boron concentrations have been determined for the synthesis of single-phase lithium niobate batches for use in the production of optically uniform single crystals and pore-free piezoelectric ceramics.

Batievaite-(Y), Y 2 Ca 2 Ti[Si 2 O 7 ] 2 (OH) 2 (H 2 O) 4 , is a new mineral found in nepheline syenite pegmatite in the Sakharjok alkaline massif, Western Keivy, Kola Peninsula, Russia. The pegmatite mainly consists of nepheline, albite, alkali pyroxenes, amphiboles, biotite and zeolites. Batievaite-(Y) is a late-pegmatitic or hydrothermal mineral associated with meliphanite, fluorite, calcite, zircon, britholite-group minerals, leucophanite, gadolinite-subgroup minerals, titanite, smectites, pyrochlore-group minerals, zirkelite, cerianite-(Ce), rutile, behoite, ilmenite, apatite-group minerals, mimetite, molybdenite, and nickeline. Batievaite-(Y) is pale-cream coloured with white streak and dull, greasy or pearly luster. Its Mohs hardness is 5–5.5. No cleavage or parting was observed. The measured density is 3.45(5) g/cm 3 . Batievaite-(Y) is optically biaxial positive, α 1.745(5), β 1.747(5), γ 1.752(5) (λ 589 nm), 2 V meas. = 60(5)°, 2 V calc. = 65°. Batievaite-(Y) is triclinic, space group P -1, a 9.4024(8), b 5.5623(5), c 7.3784(6) Å, α 89.919(2), β 101.408(2), γ 96.621(2)°, V 375.65(6) Å 3 and Z = 1. The eight strongest lines of the X-ray powder diffraction pattern [ d (Å)(I)( hkl )] are: 2.991(100)(11-2), 7.238(36)(00-1), 3.061(30)(300), 4.350(23)(0-1-1), 9.145(17)(100), 4.042(16)(11-1), 2.819(16)(3-10), 3.745(13)(2-10). The chemical composition determined by electron probe microanalysis (EPMA) is (wt.%): Nb 2 O 5 2.25, TiO 2 8.01, ZrO 2 2.72, SiO 2 29.96, Al 2 O 3 0.56, Fe 2 O 3 0.43, Y 2 O 3 11.45, La 2 O 3 0.22, Ce 2 O 3 0.33, Nd 2 O 3 0.02, Gd 2 O 3 0.07, Dy 2 O 3 0.47, Er 2 O 3 1.07, Tm 2 O 3 0.25, Yb 2 O 3 2.81, Lu 2 O 3 0.45, CaO 24.98, MnO 1.31, MgO 0.01, Na 2 O 1.13, K 2 O 0.02, F 2.88, Cl 0.19, H 2 O 6.75 (determined on the basis of crystal structure data), O = (F,Cl) −1.25, total 97.09 wt.%. The empirical formula based on the EPMA and single-crystal structure analyses is (Y 0.81 Ca 0.65 Mn 0.15 Zr 0.12 Yb 0.11 Er 0.04 Fe 3+ 0.04 Ce 0.02 Dy 0.02 Lu 0.02 La 0.01 Tm 0.01 ) Σ2.00 ((H 2 O) 0.75 Ca 0.70 □ 0.55 ) Σ2.00 Ca 2.00 (□ 0.61 Na 0.25 ( H 2 O) 0.14 ) Σ1.00 (Ti 0.76 Nb 0.15 Zr 0.09 ) Σ1.00 [(Si 3.91 Al 0.09 ) Σ4.00 O 14 ]((OH) 1.56 F 0.44 ) Σ2.00 ((H 2 O) 1.27 F 0.73 ) Σ2.00 . The infrared spectrum of the mineral contains the following bands (cm −1 ): 483, 584, 649, 800, 877, 985, 1630, 1646, 1732, 3426. Batievaite-(Y) belongs to the rosenbuschite group minerals and is the Na-deficient Y-analogue of hainite. The mineral is named in honour of the Russian geologist Iya Dmitrievna Batieva (1922–2007) in recognition of her remarkable contribution into the geology and petrology of metamorphic and alkaline complexes of the Kola Peninsula.

Double complex compounds having the [Cr(ur)(6)][Co(C2O4)(3)] center dot 4H(2)O (I) and [Cr(ur)(6)][Co(CN)(6)] center dot 3H(2)O (II) compositions were synthesized and characterized using the IR spectroscopy, elemental analysis, X-ray diffraction, crystal optical and thermal analyses. The compound I is anisotropic turquoise crystals with a needle and needle-fiber shape and a length of 5-15 mu m. The refractive indixes are N'(p) = 1.53; N'(g) = 1.56. The compound II is anisotropic lamellar pale-green crystals with refractive indixes of N'(p) = 1.55; N'(g) = 1.64. According to thermal analysis curves, the crystallization water is removed the first. The dehydrated products are resistant up to 170-180 degrees C. There is a fast weight loss from 200 to 300 degrees C, which is almost the same in both cases (about 37%). The residue of the complex I after calcination is 20.9% in air and 16.1% in argon. For complex II, they are 23.6% and 26.4%, respectively. A comparative study of the thermolysis for these complexes in air, argon, and hydrogen was carried out. The gaseous and solid thermolysis products of the complexes for different temperature ranges were analyzed. It was determined that the gaseous thermolysis products are NH3, CO, CO2, HCN, and HCNO. Regardless of the medium, the thermolysis of complex I gives an intermediate with a composition of Cr(ur) Co(C2O4)(3) at the temperature of about 300 degrees C. The amount of carbon released as CO and CO2 and remaining in the solid residue at all temperatures is close to 70%, so at least 30% is the urea released in the invariable form and as isocyanic acid and others. This also applies to complex II. The urea behaves identically in both cases. At thermolysis of complex II, no intermediate is formed and in the inert environment, the amount of original carbon, remaining in the solid residue, is much greater than for I, due to decomposition of cyano groups with nitrogen emission. As a result of thermolysis in atmospheric air and in hydrogen, both the compounds give products with similar carbon contents. Substituting of iron on cobalt in the composition of the complex anion has no appreciable effect on the course of the thermolysis of either the oxalate or cyanide complex.

For growing single crystals of lithium tantalate of optical quality with high homogeneity of their composition and desired concentration of dopant of samarium a method for producing a solid precursor Ta2O5〈Sm〉 and homogeneously doped charge LiTaO3〈Sm〉 of a congruent composition was developed. X-ray diffraction analysis and IR spectroscopy were used to study the phase composition of Ta2O5〈Sm〉 and LiTaO3〈Sm〉. Conditions for preparation of the monophasic charge LiTaO3〈Sm〉 were determined: (Sm concentration in Ta2O5 ≤ 1.5 wt %, the molar ratio [Li2O]/[Ta2O5] = 0.941, synthesis temperature 1200°C). By mass spectrometry with inductively coupled plasma and sampling by laser ablation a distribution of the dopant of samarium in Ta2O5〈Sm〉 and LiTaO3〈Sm〉 was examined and the chemical homogeneity of the synthesized products was confirmed.

Minerals of the gadolinite-(Y)-hingganite-(Y) series pertaining to the gadolinite-datolite group have been found in the alkali granite pegmatites of the Kola Peninsula. Gadolinite-(Y) is distinguished by its unique natural crystalline state. The unit-cell parameters of this mineral have elevated values as compared with those of gadolinite-(Y) from other deposits and occurrences: (i) a = 10.11 Å, b = 7.63 Å, c = 4.79, V = 369.30 Å 3 ; (ii) a = 10.05 Å, b = 7.69 Å, c = 4.76, V = 367.99 Å 3 . The increase in unit-cell parameters is not correlated with variation in chemical composition. The variable chemical compositions of particular individuals, especially as concerns REE and Y contents, assume two gadolinite-(Y) generations being contained in the intragranite pegmatites. Gadolinite-I is characterized by a high LREE content (LREE N /HREE N = 1.6) with a prevalence of total REE over Y (REE/Y = 1.36). Gadolinite-II is significantly depleted in LREE (LREE N /HREE N = 0.3) with a prevalence of Y over REE (REE/Y = 0.29). Hingganite-(Y), which has also been found in the alkali granite pegmatites of the Kola Peninsula for the first time, is characterized by elevated unit-cell parameters as well: a = 10.05 Å, b = 7.72 Å, c = 4.76 Å, V = 369.12 Å 3 . The mineral is enriched in Ca (up to 5 wt % CaO); and, by contents of REE and Y, the hingganite-(Y) from inter-granite pegmatites keeps the marginal position between its Y-dominant and REE-dominant varieties. The chondrite-normalized REE patterns assume that hingganite-(Y) crystallizes between the first and the second generations of gadolinite-(Y) and that alkali intragranite pegmatites are formed at the late magmatic stage, whereas amazonite-bearing pegmatites are formed under postmagmatic hydrothermal conditions.

We have studied conditions for the synthesis of niobium pentoxide and a lithium niobate growth charge doped with dysprosium, which was added to niobium hydroxide obtained through extraction processing of rare-metal-containing raw materials. The phase composition of Nb2O5〈Dy〉 precursors was determined by X-ray diffraction and IR spectroscopy. Using inductively coupled plasma mass spectrometry in combination with a laser ablation sampling system, we examined the Dy dopant profile in Nb2O5 powder samples and the LiNbO3 growth charge. The Nb2O5 precursors and the growth charge synthesized using them were shown to be chemically uniform in composition. The present results are of importance for the growth of defect-free lithium niobate single crystals of optical quality, highly uniform in composition, with a predetermined doping level.

The main physicochemical properties of the extracts, such as density, viscosity, and conductivity, as well as the mutual solubility of the phases in the ROH-H2O and ROH-H2O-H3PO4 extraction systems, where ROH (R = C5–C10) stands for higher monofunctional aliphatic alcohols with a different length and structure of the hydrocarbon radical, have been studied in water and aqueous solutions containing phosphoric acid. The properties correlate with the length and structure of the hydrocarbon chain in the aliphatic alcohols, as well as with the concentration of mineral acid in the extracts.

Изучены условия синтеза пентаоксида ниобия и шихты ниобата лития, содержащих примесь диспрозия в различных концентрациях, вводимую в гидроксид ниобия, получаемый на стадии экстракционной переработки редкометалльного сырья. Методами рентгенофазового анализа и ИК-спектроскопии исследован фазовый состав прекурсоров Nb2O5 Dy . Методом масс-спектрометрии с индуктивно связанной плазмой и пробоотбором с помощью лазерной абляции изучено распределение легирующей примеси Dy в порошковых образцах Nb2O5 и шихты LiNbO3. Показано, что прекурсоры Nb2O5 и синтезированная из них шихта химически однородны по составу. Результаты важны для выращивания бездефектных монокристаллов ниобата лития оптического качества с высокой однородностью состава и заданной концентрацией легирующей примеси.

Изучены основные физико-химические свойства (плотность, вязкость и удельная электропроводность) экстрактов и взаимная растворимость фаз в экстракционных системах с высокомолекулярными одноатомными алифатическими спиртами ROH (R = C5 C10) с различной длиной и структурой углеводородного радикала в воде и водных растворах, содержащих фосфорную кислоту: ROH H2O и ROH H2O H3PO4. Установлена корреляция свойств с длиной и строением углеводородного радикала алифатического спирта и концентрацией минеральной кислоты в экстрактах.