The main goal of research in the field of the structure and properties of minerals, their crystal chemistry and physics is to obtain fundamental information about the real atomic and electronic structure of mineral objects and physical regularities of their transformation under the influence of external factors (temperature, pressure, radiation, and environmental chemistry).

   Such information is the basis for typification, restoration of the conditions for mineral crystallization and evolution in a certain geological situation. It is widely used in petrogenetic and geochronological constructions. Such studies are also relevant in the development of nature-like technologies for obtaining new promising functional materials. Research in these areas remains relevant today. This thematic special issue of Lithosphere continues the similar one (“Lithosphere (Russia)”, 2024. Volume 24. No. 2); it presents 13 articles dedicated to the consideration of the following problems: (1) studies of the structure, crystal chemistry, physics and typomorphism of minerals; (2) development of methods of the synthesis and study of the properties of mineral-like materials; (3) development of research methods. The articles of the special issue reflect the results of research by Russian scientists obtained in these areas recently.

   Research subject. Structures of minerals with filled octahedral, tetrahedral, and trigonal voids in anionic packages.

   Aim. Analysis of the correlation of L. Pauling's rule of parsimony with variety of minerals.

   Key points. Using the example of the interrelation between following crystal structures: olivine, norbergite, chondrodite, humite, clinohumite, СdI₂, Mg(OH)₂, rutile, brookite, anatase, spinel, diaspore, goethite, groutite, stenierite, ramsdellite, VO₂, hollandite, todorokite, romanechite, corundum, karelianite, eskolaite, hematite, tetradymite, ilmenite, calcite, magnesite, siderite, rhodochrosite, dolomite, kutnohorite, ankerite, topaz, wurtzite, sphalerite, chalcopyrite, stannite, germanite, enargite, sulvanite, pentlandite, litharge, LiOH, cuprite, cooperite, chalcocite, BCl₃, Na₃As, covellite and domeykite, a variety of possible topological structures of crystal structures with the presence of various voids in a tightly packed motif of anions, which can be occupied by smaller cations, is demonstrated. Octahedral motifs of various stoichiometry of the ratio of ions forming the package to filled voids, tetrahedral motifs with layers of the same parity and different parity, anion-centered tetrahedral motifs, and trigonal motifs are analyzed.

   Conclusions. The explanation for the apparent contradiction between the observed topological diversity of polyhedral motifs and L. Pauling’s fifth rule is given.

   Research subject. Currently, the symmetry of schüllerite and the choice of space group (sp. gr.) in its structure are subjects of debate. In this work, a re-examination of the holotype sample of schüllerite was conducted.

   Materials and Methods. The mineral schüllerite was found in the Löhley basalt quarry (Eifel volcanic area, Germany). The crystal structure was studied using single-crystal X-ray analysis.

   Results. We refined the crystal structure of schüllerite within two space groups – acentric P1 and centrosymmetric P1 using data sets for 2496 and 1683 independent reflections with I > 3σ(I), respectively. The final R-factor values were 4.42 % in sp. gr. P1 and 4.51 % in sp. gr. P1 . The parameters of the triclinic unit cell are: a = 5.4055(3) Å, b = 7.0558(3) Å, c = 10.1945(6) Å, α = 99.838(4)°, β = 99.715(5)°, γ = 90.065(4)°, V = 377.43(4) Å3. The idealized formula is Ba₂Na(Mn,Ca)(Fe³⁺,Mg,Fe²⁺)2Ti₂(Si₂O₇)₂(O,F)₄.

   Conclusions. The acentric space group P1 is proposed as more suitable for describing the structure of schüllerite, as it allows for the identification of more existing differences in site occupancies and cation-anion bond lengths in HOH modules.

   Object of Study. The symmetry and the choice of the space group (sp. gr.) for the structures of perraultite and related minerals – bafertisite-like Mn/Fe-Ti heterophyllosilicates with ordered alkali and alkaline earth cations is still under discussion. In the present work, the crystal structure of the Ca-containing member of the perraultite series is studied.

   Materials and Methods. The mineral perraultite used in this research was collected from the Oktyabrsky alkaline massif (Northern Azov Sea region). The crystal structure of the sample was studied using single crystal X-ray diffraction analysis. The parameters of the monoclinic unit cell are: a = 10.7230(3) Å, b = 13.8313(4) Å, c = 20.8178(7) Å, β = 95.0348(3)°, V = 3075.638(15) Å3.

   Results. The crystal structure of perraultite was refined within two space groups, C2 and C2/m, using data sets for 5120 and 2948 independent reflections with I > 3σ(I), respectively. The final R-factor values were 4.66 % for the sp. gr. C2 and 4.84 % for sp. gr. C2/m. For the structural model refined using the sp. gr. C2 the crystal chemical formula is (Z = 2): A1(Ba) A2(Ba_0.64K_0.36)₂ A3(K_0.87Ba_0.13) B1(Na_0.70Ca_0.30) B2(Na_0.70Ca_0.30) B3(Na_0.90Ca_0.10)₂ [M1(Mn_0.50Fe²⁺_0.40Zn_0.10) M2(Mn_0.60Fe²⁺_0.30Zn_0.10) M3(Mn_0.50Fe²⁺_0.50) M4(Mn_0.70Fe²⁺_0.30) M5(Mn_0.50Fe²⁺_0.50) M6(Mn_0.60Fe²⁺_0.40) M7(Mn_0.60Fe²⁺_0.40) M8(Mn_0.70Fe²⁺_0.30) (OH)₄]₂ [Ti1(Ti_0.91Nb_0.09) Ti2(Ti_0.91Nb_0.09) Ti3(Ti_0.77Nb_0.13Zr_0.10) Ti4(Ti_0.91Nb_0.09) (Si₂O₇)₄O₄F₂]₂, where square brackets denote the main structural fragments.

   Conclusions. The sp. gr. C2 is proposed as more suitable for describing the perrotite-type structure, since it allows better identification of the features of the occupancy of positions within the HOH modules. The studied mineral from the Oktyabrsky massif is a F-dominant analogue of perraultite, differing from the latter also by the presence of calcium, a high iron content and a low niobium content.

   Research subject. Two varieties of frankamenite, green and lilac-gray, were discovered in the charoite rocks of the Murun massif.

   Aim. The aim of this study is a comparative analysis of lilac-gray and green frankamenite samples.

   Materials and Methods. The mineral composition of frankamenite-containing charoite rocks was studied by optical petrographic method using polarization microscope, the chemical composition was studied on electron probe microanalyzer. Crystal structure of frankamenite was studied using single crystal automatic diffractometer, and absorption and photoluminescence spectra were obtained on spectrophotometer and spectrofluorometer respectively.

   Results. The morphogenetic features of rock samples containing frankamenite, its paragenetic associations and relationships with associated minerals were studied. In terms of chemical composition, the Na₂O and CaO contents in the samples are almost identical to the previously studied Murun samples, while the K₂O level for lilac-gray and green frankamenite is higher than in the analyses of other authors. The crystal structure of green frankamenite was also studied, compared with the lilac-gray sample, and absorption and photoluminescence spectra were analyzed.

   Conclusions. Both varieties of the mineral differ in their associations of minerals: green frankamenite is usually associated with charoite, aegirine, microcline and quartz, while lilac-gray frankamenite is associated with charoite, amphibole, quartz, steacyite and apatite. Using EPR, optical absorption and photoluminescence methods, it was established that the green color of frankamenite is associated with Fe/Ti and Fe²⁺/Fe³⁺ charge transfer transitions.

   Research subject. Cu-poor bornite from copper ores of Volkovskoye deposit (Middle Urals).

   Materials and methods. Specimens with bornite have been sampled from the industrial copper ores at the North-West quarry of the Volkovskoye deposit. Properties of the bornite have been studied in dynamics with optical microscopy in reflected light, energy dispersive spectroscopy, Raman spectroscopy; optical properties have been analyzed using diffusion reflectance spectroscopy.

   Results. Absence of elements diffusive processes into the subsurface layer from bulk bornite during mechanical treatment has been demonstrated, at the surface changing the bornite composition stays be saved in the limits of the measurements accuracy by energy dispersive spectroscopy. The dynamics of surface properties changes for the Cu-poor pink bornite using diffusion reflectance spectroscopy has been established.

   Conclusions. On the basis of the study results a new approach to develop a quantitative criterion for bornite varieties determination for mineralogical-technological mapping and prediction of processing indicators of copper ores has been proposed.

   Research subject and Methods. New data on the impurity composition, Raman spectra and photoluminescence of noble spinel from marbles of the Eastern Slope of the Southern and Middle Urals – the Kuchinsky occurrence (Kochkarsky anticlinorium) and the Alabash occurrence (Murzinsky-Aduysky anticlinorium), as well as the Kukh-i-Lal and Goron deposits (Southwestern Pamir) are presented.

   Results. Energy dispersion microanalysis of the chemical composition shows a high chromium content up to #Cr = Cr/(Cr + Al) ~ 0.2 and a low iron content, as well as a deviation in the ratio of divalent and trivalent cations from the stoichiometric in spinel from the Kuchinsky occurrence. The two-mode frequency behavior has been established by Raman spectroscopy in the entire range of compositions corresponding to spinel-magnesiochromite solid solutions. The tetrahedral sublattice vibration parameters – the frequency of the breathing mode and the width of the bending mode of the MgO₄ groups – are characterized by the highest concentration sensitivity. The reaction of the spinel tetrahedral sublattice is qualitatively similar when the structure is disordered due to (1) the isomorphous substitution VICr³⁺ → ^VIAl³⁺, (2) the thermally induced inversion ^IVMg²⁺ → ^VIAl³⁺, ^VIAl³⁺ → ^IVMg²⁺, (3) the radiation defects; for the analysis of quantitative differences, a diagram "width of the mode of deformation vibrations MgO₄ vs. frequency of the lattice mode T(Mg)" is proposed. Variations in the structure and properties of the Cr³⁺ emission center under disordering have been determined by low-temperature photoluminescence spectroscopy.

   Conclusions. The vibrational properties and photoluminescence of chromium ions are determined by several interrelated factors: (1) impurity composition, (2) nonstoichiometry, (3) structure inversion, (4) vacancy defects. The position and relative intensity of zero-phonon N-lines resulting from the Cr³⁺ emission center distortions are proposed for use as highly sensitive structural probes, in particular, to assess the gemological value of the spinel. The features of the composition, structure, and luminescent properties of the samples of the Kuchinsky occurrence formed at the progressive stage of regional metamorphism under conditions of increasing temperature and pressure are revealed.

   Object of the study and methods. Electrical characteristics of demantoid from clinopyroxenites (Poldnevskoye deposit, Middle Urals) and two samples of andradite 1-2 from skarns (Verkhniy Ufaley, Middle Urals; Sokolovsky mine, Rudny, Kazakhstan) were studied by impedance high-temperature spectroscopy in the heating-cooling mode at temperatures of 200–900 °C and frequencies of 1–106 Hz using of platinum and lanthanum-strontium cobaltite electrodes. Thermogravimetric, X-ray diffraction and diffuse light scattering data are presented.

   Results. Experimental chemical formulas of andradite 1-2 and demantoid are (Mg_0.24Ca_3.16Mn_0.04)(Fe_1.63Al_0.33)Si_2.95Ti_0.05O_12.14, (Ca_3.49Mn_0.04)(Fe_1.79Al_0.51)Si_2.94Ti_0.06O_12.97, (Ca_3.51Mn_0.01) (Fe_2.49Al_0.05Cr_0.0038)Si_3.00O_13.34, respectively. Andradite 1 contains up to ~20 % clinochlore impurity and an insignificant content of ferrobustamite impurity; in andradite 2 – no more than ~8 % of isostructural impurity of hydroandradite; demantoid does not contain phase impurities, while the peaks of the garnet phase are asymmetric due to the presence of two phases with the garnet structure. In the optical spectra of andradite 1-2, a wide band is observed in the near UV region and a significant number of sufficiently wide bands in the visible region associated with the absorption of Fe²⁺, Fe³⁺ and Ti⁴⁺ ions; Spectra of annealed samples of andradites at 750 °С are similar. For demantoid, a wide absorption band of 860 nm is observed, it shifts to 700 nm after annealing; it is assumed that the 860 nm band is associated with Cr²⁺ ions, which undergo additional oxidation during annealing. The Arrhenius dependences of the electrical conductivity of andradite 1 during heating and cooling differ from each other due to the presence of impurity phases (mainly clinochlore) in the sample. Dependencies for andradite 2 and demantoid in heating-cooling mode are close to each other, while the electrical conductivity of andradite 2 is higher than that of andradite 1. At temperatures of 750–775 °C, demantoid has the highest conductivity; while the Cr impurity does not make a significant contribution to its conductivity.

   Conclusions. Electrical characteristics of demantoid were obtained for the first time; Arrhenius dependences of two andradites of different chemical and phase composition were analyzed; it was shown that the composition has a significant effect on electrical conductivity. The obtained data can be used to construct geoelectric models of fragments of the earth's crust with the corresponding minerals.

   Research subject and Methods. The electrical characteristics of an almandine sample from the Verkholovskaya garnet mine (Middle Urals, Russia) were studied using high-temperature impedance spectroscopy in both heating and cooling modes, over a temperature range of 200–900 °С and a frequency range of 1–106 Hz. For this method, electrodes made of platinum and lanthanum-strontium cobaltite were employed. The results were interpreted in combination with thermogravimetric data, X-ray diffraction XRD analyses and diffuse light scattering measurements for almandine powders in their initial state, after annealing at 750 °С and for model synthetic iron oxide Fe₂O₃.

   Results. In the cooling mode, a linear dependence was observed with a break in the temperature range of 600–625 °С with characteristic activation energies E_a ^⬚ 0.58 and 0.81 eV in the low-temperature (200–625 °С) and high-temperature (625–900 °С) regions, respectively. During the heating-cooling cycle an anomaly was noted at 750 °С, where the sample’s resistance remained constant or changed insignificantly with increasing temperature. Analysis of impedance spectroscopy data revealed the onset of decomposition of the almandine sample already at 750 °С. Previously, no changes in phase composition had been reported at this temperature. The initial stage of almandine destruction is accompanied by the formation of nanosized particles of iron oxide Fe₂O₃ on its surface, which was confirmed by diffuse light scattering data. Traditional methods of detecting changes in phase composition (TG-DTA and X-ray phase analysis) indicate the appearance of the Fe₂O₃ phase only at temperatures above 750 °С. This may be associated with their insufficient sensitivity and/or the specific morphology of the released Fe₂O₃ phase.

   Conclusions. The impact of minor changes in the phase composition of compounds (initial stages of phase transformations) highlights the potential of impedance spectroscopy as a valuable tool for recording and investigating the early stages of thermal decomposition of both minerals and synthetic materials.

   Subject of Research. Methodological aspects of sample preparation and electron backscatter diffraction (EBSD) in the study of microdeformations in zircon grains.

   Objects and Methods. Fragments of impactites from shock-metamorphosed rocks of the Vredefort (South Africa) and Kara (Pay-Khoy Ridge, Yugorsky Peninsula, Russia) impact craters were investigated using scanning electron microscopy (SEM) and electron backscatter diffraction.

   Results. The identification of zircon grains with specific microdeformations requires high-spatial-resolution (tens of nanometers) examination of large polished rock surfaces, which demands significant instrument time. To reliably detect microdeformations in zircon, the following methodological challenges were addressed: (1) analyzing the influence of Electron Backscatter Diffraction Pattern (EBSP) imaging conditions at different beam accelerating voltages (10, 20, and 29 kV) on the signal-to-noise ratio, spatial resolution, and Kikuchi band width; (2) comparing zircon grain orientation maps obtained at different voltages; (3) developing an algorithm for mineral identification and microdeformation finding; and (4) validating the methodology on zircon grains from the Vredefort and Kara impact craters.

   Conclusions. The sample preparation methodology for EBSD analysis was refined, and methods for processing EBSD data to improve Kikuchi diffraction pattern indexing were explored. The efficiency of detecting and analyzing shock-metamorphosed zircon grains using scanning electron microscopy was enhanced through optimized electron imaging and EBSD mapping conditions. An algorithm for mineral identification in thin sections (rock slices) was developed. The methodology was validated on a series of 50 thin sections from the Kara and Vredefort impactites, resulting in the identification of 436 zircon grains, including all known types of zircon microdeformations.

   Research subject. Quartzites from Different Sites of the East Sayan Quartz-Bearing Region.

   Aim. The aim of this study is to apply machine learning methods to effectively classify quartzite samples by their chemical composition, including the identification of key trace elements such as manganese and the detection of geochemical differences between samples.

   Materials and methods. The study used chemical analysis data from 776 quartzite samples, which were interpreted using machine learning methods. Standard data preprocessing techniques such as normalization were applied as well as data augmentation using SMOTE to solve the class imbalance problem. As a result, the CatBoost algorithm was selected, which showed high classification accuracy.

   Results. Cross-validation results showed that the CatBoost algorithm achieved classification accuracy of up to 97 %. The importance of features indicates that manganese is a key element in the classification of samples, while elements such as aluminum and potassium have a supporting effect. The analysis of the classification by color of quartzites with an accuracy of 0.94 was also successfully carried out.

   Conclusions. The study demonstrates the effectiveness of applying machine learning methods to the analysis of the chemical composition of quartzites, providing new opportunities for geochemical and archaeological research.

   Research subject. A series of mineral-like phases with strontiowhitlockite structure (1–x)Sr₉In(PO₄)₇–_xCa₉Ln(PO₄)₇ Ln = Eu³⁺, Yb³⁺.

   Aim: An analysis of phase formation patterns and crystal-chemical characteristics influencing the crystallization of mineral-like phases within the studied series.

   To achieve the aim, the following set of Materials and Methods is used: the powder X-ray diffraction (PXRD), the second harmonic generation (SHG), dielectric spectroscopy, the photoluminescence spectroscopy.

    Results. Doped phosphates with strontiowhitlockite structure were synthesized by a high temperature solid-state method. The structure was confirmed through X-ray diffraction method. The PXRD patterns of all samples were compared with strontiowhitlockite-type phosphate Sr₉In(PO₄)₇. There was an absence of SHG signals, conforming the non-polar structure. The λ-maximum is observed in the temperature dependence of the dielectric constant for all sensitized samples, while no anomalies were recorded on the loss tangent. The similar behaviour in dielectric curves may indicate isostructurality of studied samples, and crystallisation in non-polar space group. It was shown that samples demonstrate stable photoluminescence in red-orange region for Eu³⁺-doped phosphates, while Yb³⁺-doped ones shown IR-photoluminescence properties.

   Conclusions. A series (1–x)Sr₉In(PO₄)7–xCa₉Ln(PO₄)₇ was crystallised in Sr₉In(PO₄)₇ structure, where Sr²⁺ sites, with coordination number equals to 8, were substituted by Ca²⁺ and Eu³⁺. Such ions cannot occupy In³⁺ site, which is presented by small octahedral, due to high ionic radius difference between ions. However smallest ion as Yb³⁺ can occupy small octahedral site. Dielectric and photoluminescence properties were studied in (1–x)Sr₉In(PO₄)₇–_xCa₉Ln(PO₄)₇.

   Research subject. A series of experiments on the synthesis of ferrous djerfisherite by the isobaric-isothermal holding method were carried out. We used standard autoclaves made of alloy steel with a volume of 200 cm³ as high-pressure vessels. The starting material for the synthesis was a mixture of FeS₂ (pyrite) + Fe₂O₃ + K₂CO₃ + KCl, ground into powder, metallic aluminum and fluid (water + ethanol) were used to maintain reducing conditions.

   Aim. To establish the optimal parameters for the synthesis of djerfisherite and to obtain a representative amount of djerfisherite for further studies of its stability under controlled conditions (T, P, fO₂, etc.).

   Methods. In order to identify the obtained phases, we first carried out X-ray diffraction analysis and then Raman spectroscopy; scanning electron microscopy with energy-dispersive spectrometry were used to determine the chemical composition of all newly formed phases.

   Results. Djerfisherite of the composition K₆Fe_24.5S₂₆Cl was synthesized together with troilite ± sylvite. Semi-quantitative ratios of newly formed phases indicate the presence of djerfisherite in amounts from 30 to 80 wt %. The Raman spectra of synthetic djerfisherite correspond to previous studies.

   Conclusions. Favorable parameters for the synthesis of djerfisherite are: T = 500°C, P = 500 atm, t = 168 hours. As a result of experiments we synthesized djerfisherite (72 wt %), together with troilite (21 wt %) and sylvite (7 wt %), with a total mass of about 15 g.

   Research subject. Calcium-magnesium phosphate powder and cement materials and cement fluid containing sodium carboxymethylcellulose (CMC).

   Aim. To develop injectable bone cements based on soluble phases of calcium and magnesium phosphates for possible use in minimally invasive surgery.

   Methods. Fritsch Analysis 22 laser particle analyser, Shimadzu XRD-6000 diffractometer, Tescan Vega II scanning electron microscope with an Oxford Instruments Inca X-Act energy dispersive analyser, Tristar 3000 particle analyser, Brookfield DV2T viscometer, Instron 5581 and Instron 3382 universal testing machines were used to characterise the materials.

   Results. The introduction of CMC resulted in an increase in the viscosity and surface tension of the cement fluid, which resulted in an increase in the injectability and cohesion in aqueous media of the resulting cement materials. The effects of CMC introduction and mechanochemical activation on the phase composition, setting time, microstructure, cohesion, injectability and strength properties of the cement materials were determined.