卷 70, 编号 2 (2025)

The major milestones in the centennial history of the Department of Crystallography at St. Petersburg State University—the oldest crystallography department in Russia—are reviewed. It is demonstrated that the St. Petersburg crystallographic school traces its origins to the renowned Russian scientist E.S. Fedorov (1853–1919). The main research areas of the department’s staff are outlined, including crystal morphology, crystal optics, crystal growth, crystal chemistry, crystal physics, and X-ray diffraction analysis. Biographical information is also provided on the department’s heads: O.M. Ansheles, V.B. Tatarsky, V.A. Frank-Kamenetsky, S.K. Filatov, and Y.O. Punin.

This review presents data on the crystal chemistry and genetic mineralogy of all known natural anhydrous sulfates with species-defining alkali cations—Na or/and K (61 mineral species, 48 structural types). These minerals are primarily associated with two genetic mineralization environments: volcanic fumaroles and evaporites. Both environments are characterized by low (atmospheric) pressure but differ significantly in temperature and crystallization mechanisms. Based on structural classification, the studied minerals are divided into two major groups: (1) those with an anionic motif consisting solely of SO₄ tetrahedra (sometimes including additional anions such as F, Cl, or CO₃), and (2) those with heteropolyhedral anionic motifs composed of SO₄ tetrahedra and polyhedra of cations with relatively high-strength characteristics (e.g., Mg, Mn, Zn, Cu, Fe, V, Al, Bi, Mo, As, Te, and occasionally Ca). This classification aligns with genetic types: the first group predominates in evaporitic environments, while the second group is more common in fumarolic settings. A clear positive correlation has been established between the degree of polymerization of the heteropolyhedral anionic motif and the number of minerals in which such motifs occur. Specifically, 18 minerals exhibit frameworks or pseudo-frameworks of varying topologies, 11 minerals feature layered motifs, eight minerals contain chain-like motifs, and only one mineral contains isolated heteropolyhedral complexes. Additionally, the review discusses various types of solid-solution breakdown and other solid-state transformations in high-temperature sulfates with aphthitalite-like structures from volcanic fumaroles.

A review of structural studies of silver borates with salt-inclusion structures is presented. Data on the first halogen-containing silver borates are provided, along with the structural and physicochemical characterization of the Ag₄B₄O₇X₂ (X = Br, I), Ag₃B₆O₁₀X (X = Br, I, NO₃), Ag₄B₇O₁₂X (X = Cl, Br, I) families, as well as Ag₄(B₃O₆)(NO₃) and Ag₃B₄O₆(OH)₂(NO₃). The crystal structures of these compounds are framework-type, layered, or composed of isolated boron-oxygen groups. In almost all cases, silver atoms exhibit pronounced anharmonicity in thermal displacements, which was investigated using X-ray structural analysis, including extensive temperature-dependent studies. The reasons for the low stability of chlorine-containing silver borates are discussed, along with the relationship between the anharmonicity of thermal displacements and other properties, such as the high ionic conductivity of Ag₃B₆O₁₀I.

In this study, we present an investigation of the thermal behavior of natural and synthetic phosphates and sulfates with an antiperovskite-type structure, where the anion-centered octahedron is the main structural unit. We discuss examples of the thermal behavior of antiperovskites with classical and hexagonal 3D frameworks (K₃SO₄F, Rb₃SO₄F, synthetic analogue of kogarkoite Na₃SO₄F, galeite Na₁₅(SO₄)₅ClF₄, schairerite Na₂₁(SO₄)₇ClF₆); with one-dimensional (1D) chains of corner- and face-sharing octahedra (nacaphite Na2CaPO4F and its synthetic dimorph, synthetic analogue of moraskoite Na₂CaPO₄F, nefedovite Na₅Ca₄(PO₄)₄F); and with clusters represented by trimers of anion-centered octahedra (synthetic analogue of arctite (Na₅Ca)Ca₆Ba(PO₄)₆F₃). Based on the obtained data, some general patterns were identified, depending on the structural topology and thermal stability of antiperovskites.

The paper summarizes the data on the structures of hydrotalcite group minerals – layered double hydroxides with the general formula M²⁺ ₆ M³⁺ ₂ (OH)₁₆A^m– _2/m·4H₂O (М²⁺ = Mg²⁺, Ni²⁺; М³⁺ = Al³⁺, Fe³⁺, Cr³⁺, Mn³⁺, Co³⁺; A = CO₃^2–, Cl^– and OH^–). It is shown that all of them crystallize with the structure of 3R- and 2H-polytypes without the formation of superstructures. The a unit-cell parameter is in the range of 3.05–3.13 Å. The characteristic interlayer distances (d_00n) for the members of the group with carbonate and chloride anions are ~7.80 and 8.04 Å, respectively (c = d_00n × 2 for 2H and c = d_00n × 3 for 3R). Three hydrotalcite group minerals should be reconsidered taking into account new crystallographic data and regularities: takovite and droninoite most likely correspond to minerals of the quintinite group with M²⁺ : M³⁺ = 2 : 1, rather than to minerals of the hydrotalcite group, and the data on reevesite indicate that this name could describe two minerals with M²⁺ : M³⁺ = 3 : 1 and 2 : 1.

The geometric aspects of molecular crystal packing in cubic and hexagonal crystal systems are examined. It is shown that, during the packing of asymmetric molecules into a crystal, one of the key geometric factors influencing the prevalence of a particular symmetry group is the proportion of forbidden regions (excluded volume) within the unit cell where molecules cannot be accommodated. Symmetric molecules predominantly occupy special positions, which correspond to dense or closest sphere packings. A list of regular systems of space groups in cubic and hexagonal systems has been derived, whose regular point systems can describe dense molecular packings in terms of closest sphere packings.