Crystal-chemical features of high-calcium and hypercalcium eudialyte-group minerals (EGMs) from a carbonatite-related rock of the Tamazeght peralkaline complex, High Atlas Mountains, Morocco were studied using electron probe microanalysis, single-crystal X-ray structure analysis, infrared and Raman spectroscopy. The major components of the host rock are calcite, fluorite and EGMs; aegirine-augite is present in subordinate amounts. The specific features of the studied EGMs are chemical heterogeneity, a complex zoning, reaction zones around calcite and apatite inclusions, Na- and Cl-deficiency, high contents of Ca, Mn, REE, Nb, carbonate and H-bearing groups, positive correlation between Nb and Mn and negative correlations between the pairs Fe-Mn and Zr-Mn. These features confirm previous assumptions about the role of infiltration of carbonatite fluid rich in Ca, Mn, REE, Nb, CO2 and H2O and a depletion of Cl in the remaining fluid after the crystallization of sodalite at the expense of nepheline in the formation of carbonatite-related rocks of the Tamazeght complex. The crystal structure of a single-crystal fragment extracted from the Nb-rich zone refined to R-1 = 0.0335 has shown a high degree of ordering of Na, REE and H3O+ and the dominance of Fe3+ at the M2 site with five-fold coordination. The composition of EGMs from the reaction zones around calcite and apatite inclusions corresponds to Mn-dominant (with Mn > Fe at the M2 site) analogue of feklichevite with the simplified formula Ca-3(Na,K)(9)(H3O)(3)Ca6Zr3(Mn2+,Fe3+,Zr)(3)NbSi(Si24O72)(OH,H2O)(5)(F,Cl)(2/3)(CO3)(1/3).

The re-study of the crystal structure of the second find of low-calcium and rare-earths bearing voronkovite in the Lovozero alkaline complex, Kola Peninsula has revealed new features of its structure, which lower the symmetry of the mineral. Ordering of Ca, Mn, Ce, and Na atoms in octahedra of six-membered rings, as well as Zr, Fe, and Na atoms in M2 positions, combining translationally identical six-membered rings as well as Nb, Ti, and Si atoms and vacancies in axial fragments of the structure, has been established within the P3 symmetry. The trigonal-cell parameters of the mineral are a = 14.1617(1) Å, c = 30.1815(1) Å, and V = 5242.09(4) Å3; the number of independent positions is 184. The crystal structure has been refined to the R factor of 3.74

A re-study of the crystal structure of low-calcium and high-zirconium eudialyte from the Khibiny Mountains of Kola Peninsula has revealed new features of its structure, which decrease the symmetry of the mineral. The ordering of Ca, Fe, Mn, and Na atoms in octahedra of six-membered rings, as well as Zr and Na atoms in M2 positions at the centers of square pyramids, with a common base, formed by the edges of these octahedra, has been established with the P3 symmetry. The trigonal unit cell parameters are a = 14.222(3) Å, c = 30.165(5) Å, and V = 5283.9 Å3. Taking into account the new data, the studied low-calcium eudialyte can be assigned to the subtype of oneillite or raslakite, being a high-zirconium variety of the latter. The study of the structure of this mineral in rhombohedral symmetry (sp. gr. R3m and R3) and trigonal Р3 symmetry has shown that the decrease in symmetry of the structural model of low-calcium representatives of the eudialyte group makes it possible to clarify the nature of ordering of the cations occupying key framework positions.

The nolanite supergroup has been established and approved by the IMA CNMNC. It contains eight mineral species with the nolanite-type structure. They are hexagonal with the space group P63mc and unit-cell parameters in the following ranges: a=5.5–6.0 Å and c=8.8–10.3 Å; Z=2. The nolanite supergroup is subdivided into three groups (nolanite, kamiokite, and rinmanite groups) in accordance with the largest charge of species-defining cations, which coincides with the largest charge of octahedral M cations (+3, +4, and +5, respectively). Their general formulae are M133+M23+T3+O7(OH) (nolanite group: nolanite, V43+Fe3+O7(OH); akdalaite, Al5O7(OH); and ferrihydrite, Fe53+O7(OH)), M134+M22+T2+O8 (kamiokite group: kamiokite, Fe22+Mo34+O8; iseite, Mn22+Mo34+O8; and majindeite, Mg2Mo34+O8), and (M123+M12+)M25+T2+O7(OH) (rinmanite group: rinmanite, (Fe23+Mg)Sb5+ZnO7(OH), and zincorinmanite-(Zn), (Fe23+Zn)Sb5+ZnO7(OH)). Relationships between members of each group can be described by homovalent substitution schemes, whereas relationships between different groups are determined only by heterovalent substitution schemes. All historical names of minerals belonging to the nolanite supergroup are preserved. In new minerals of the nolanite supergroup, each combination of the M1 and M2 cations defines the root name. A Levinson-type suffix should be applied to indicate the dominant component at the tetrahedrally coordinated T site. The charge-balancing M12+ cation defines the prefix (magnesio-, zinco-, mangano-, etc.).

Materials of the 2D zeolite class retain local catalytically active sites and the stability of traditional zeolites but with layered structures. Synthetic and naturally occurring single- and multilayer apophyllite-related compounds are prototypes of advanced industrial materials for use in various technologies. Their surface chemistry allows for functionalization, and these layers serve as fundamental building blocks for zeolitic frameworks. The discovery of the first triple-layer silicate, günterblassite, provided a critical link that established a fundamental crystal–chemical relationship between layered and framework structures in a wide range of micro- and mesoporous minerals and synthetic materials. The most prominent topic in the development of 2D zeolites remains the synthesis and structural characterization of these 2D zeolite structures This review offers a comprehensive overview of the current state of 2D and 3D zeolites constructed based on apophyllite-type layers. In accordance with the terms of modular crystal chemistry, we present a straightforward classification scheme based on the topological and symmetrical distinctions of the layers and provide ways for their stacking, creating a valuable basis for understanding the modular assembly of advanced porous materials.

Rerefinement of the crystal structure of the mineral tashelgite with the idealized formula CaMgFe2+Al9O16(OH) (orthorhombic Pbam space group; a = 17.1823(1), b = 23.5718(4), c = 5.6973(5) Å) is performed using the earlier obtained diffraction data. Fine crystal structure details and distribution features of cation positions are retrieved from precision Mössbauer and optical spectroscopy data. It is shown that the main motif and the pattern of cation distribution over octahedral and tetrahedral positions are preserved, despite the symmetry increase. However, due to a smaller number of independent positions, the distribution in the Pbam model becomes less ordered than in the Pc model. The appearance of tashelgite, having a complex structure based on spinel modules, agrees well with the presence of associated minerals such as spinel-like magnetite and hercynite, as well as hibonite, also containing spinel modules in its structure. A comparative crystal chemical and modular analysis of natural and synthetic compounds containing spinel modules is performed.

Microporous materials containing hydrated silanol groups Si-OH as well as hydrated proton complexes, H2n+1On+, including hydronium (n = 1), Zundel (n = 2), and Eigen (n = 4) cations, are of practical importance as potential ion exchangers and ion conductors. In this paper, we provide data on crystal-chemical features, hydrogen bonding and Raman spectra of alkaline microporous titano-, niobo-, zircono-, and aluminosilicate minerals belonging to the labuntsovite, lovozerite, eudialyte, and sodalite groups in which a part of sodium was substituted by hydrated proton complexes under low-temperature hydrothermal or supergene conditions. Most minerals studied in this work do not have synthetic analogues and are considered as possible natural prototypes of microporous materials with technologically important properties. The obtained experimental data and their comparison with the results of ab initio theoretical calculations published elsewhere show that Raman spectroscopy is an effective tool for the precise identification of hydrated proton complexes with extremely strong hydrogen bonds and estimation of corresponding O center dot center dot center dot O distances in the range of 2.37-2.68 angstrom. The presence of hydrated proton complexes in microporous silicates is a clear and sensitive geological indicator showing that a rock underwent the low-temperature alteration. Hydrated proton complexes, H2n+1On+, are widespread in minerals and inorganic materials. Raman spectroscopy is a sensitive tool for the detection of the hydrated proton complexes. Hydrated proton complexes are a geological indicator of low-temperature alterations. image

Two mineral species of the labuntsovite group from Khibiny (sample 1) and Lovozero (sample 2) alkaline massifs are analyzed by single crystal X-ray diffraction and Raman spectroscopy. They are intermediate members of the tsepinite-Na–“tsepinite-Ba”–tsepinite-K solid solution, which are characterized by a high degree of hydration and a low concentration of extra-frame cations. Parameters of monoclinic cells are: a = 14.5086(6) Å, b = 14.2174(6) Å, c = 7.8712(3) Å, β = 117.119(4)°, V = 1444.09(11) Å3 (sample 1) and a = 14.2582(4) Å, b = 13.7541(6) Å, c = 7.7770(2) Å, β = 116.893(4)°, V = 1360.20(9) Å3 (sample 2). Crystal chemical formulas (Z = 2) are: |A[Na0.84K0.6[(H2O)4]5.2]BK0.2CBa0.25D[Ca0.35Na0.15Fe0.025(H2O)]| M1(Ti1.2Nb0.8)M2(Ti1.1Nb0.9)(O,OH)4(Si4O12)2 for sample 1 and |A[Na1.6(H2O,H3O)0.4]BK2C(Ba0.51Sr0.21)D [Mn0.3Ca0.2(H2O)](H2O)4|M1(Ti1.94Nb0.06)M2(Ti1.88Nb0.12)(O,OH)4(Si4O12)2 for sample 2. The high degree of hydration of sample 1 is expressed in the presence of proton hydrate complexes and tetrahedral [H2O]4-associates. Labuntsovite group minerals (LGMs) are characterized by so-called block isomorphism due to different distributions of D cations. Our analysis of heteropolyhedral MT-frameworks in LGMs allows us to determine the topological features of cation networks.

Research subject. The crystal structure of christofschäferite-(Ce) was previously refined in terms of theP21/mlow-symmetrical space group, which allowed the local features of cationic arrangements to be determined. In this work, we set out to refine the crystal structure of christofschäferite-(Ce) in terms of theP21/ahigh-symmetrical space group based on the previously collected diffraction data. A topology-symmetrical analysis of the members of the chevkinite group with the general formula ofA4BC2D2(Si2O7)2O8was conducted.Materials and methods. A magmatic rock sample with christofschäferite-(Ce) inclusions was found in the vicinity of the Laacher See volcano, near Mendig, Eifel Mountains, Rhineland-Palatinate (Rheinland-Pfalz), Germany. The crystal structure was studied using single-crystal X-ray analysis.Results. Despite an increase in the symmetry to theP21/aspace group (in comparison with the previous data with theP21/mspace group), the main patterns of cation distribution between the octahedral and tetrahedral sites are preserved. However, due to the lover number of cationic sites, this distribution becomes more disordered. Based on a crystal chemical analysis of the crystal structures of natural and synthetic members of the chevkinite group in the framework of the OD theory, it is possible to combine them into a united OD family with the same OD groupoid.Conclusions. According to the OD theory, there are two structural OD-subgroups of the chevkinite group (chevkinite and perrierite). The crystal structure and symmetry of possible MDO-polytypes are predicted.

The crystal structure of the recently discovered eudialyte group mineral, amabellite-(Ce) Na15[(Ce1.5Na1.5)Mn3]Mn2Zr3£Si[Si24O69(OH)3](OH)2 · H2O, found in the hyperagpaitic pegmatite of the Saint-Amable massif (Canada), has been solved by X-ray structural analysis within the space group R3. Amabellite-(Ce) is a member of the eudialyte group with the lowest calcium content and differs from other members of this group by the dominance of lanthanides in the part of the edge-sharing octahedra of the six-membered ring. The unit cell parameters of the mineral are: a = 14.1340(2), c = 30.378(1) Å, V = 5255.6(3) ų. A model of the cation distribution in the crystal structure of amabellite-(Ce) within the low-symmetry space group P3 has been proposed. The obtained 162 independent positions were refined in the isotropic-anisotropic approximation of atomic displacements using 3968 F 3σ(F), R = 4.6%. Despite the fairly close results, the transition from space group R3 to P3 allows for more detailed information on the local distribution of a number of elements over the framework positions. A comparison was made between the crystal structure models of amabellite within the symmetries R3 and P3, as well as other low-calcium eudialyte group minerals previously studied within several space groups.

На основе полученных ранее дифракционных данных выполнено повторное уточнение кристаллической структуры минерала ташелгита с идеализированной формулой CaMgFe2+Al9O16(OH) в рамках ромбической пространственной группы Pbam (параметры элементарной ячейки: a = 17.1823(1), b = 23.5718(4), c = 5.6973(5) Å). Тонкие детали кристаллической структуры и особенности распределения катионов по позициям выполнены на основе прецизионных данных мессбауэровской и оптической спектроскопии. Установлено, что, несмотря на повышение симметрии, основной мотив и характер распределения катионов по октаэдрическим и тетраэдрическим позициям сохраняется. Тем не менее, из-за меньшего числа независимых позиций в модели пр.гр. Pbam распределение становится менее упорядоченным по сравнению с моделью пр.гр. Pc. Возникновение минерала ташелгита, характеризующегося сложной структурой, основу которой составляют шпинелевые модули, хорошо согласуется с наличием ассоциирующих минералов, в частности, магнетита и герцинита (структурный тип шпинели), а также хибонита, структура которого также содержит шпинелевые модули. Проведен сравнительный кристаллохимический и модулярный анализ природных и синтетических соединений, содержащих шпинелевые модули.

The crystal structure of a new mineral from the eudialyte group, amableite-(Ce) Na15[(Ce1.5Na1.5)Mn3]Mn2Zr3 □ Si[Si24O69(OH)3](OH)2 ⋅ H2O, was refined using X-ray diffraction analysis in the R3 space group. This mineral was discovered in a hyperagpaitic pegmatite in the Saint-Amable massif, Canada. Amableite-(Ce) is a representative of the eudialyte group with the lowest calcium content; it differs from other representatives of this group by the dominance of lanthanides in a part of edge-sharing octahedra of the six-membered ring. The structure of amableite-(Ce) has a unit cell with the following parameters: a = 14.1340(2) Å, c = 30.378(1) Å, and V = 5255.6(3) Å3. In this paper, we propose a model for the distribution of cations within the amableite-(Ce) crystal structure based on a low-symmetry P3 space group. We refined 162 independent atomic positions in the isotropic–anisotropic approximation using 3968 reflections with F > 3σ(F) and obtained R = 4.6

Методами рентгеноструктурного анализа и КР-спектроскопии были изучены два образца минералов группы лабунцовита из Хибинского (образец 1) и Ловозерского (образец 2) щелочных массивов – промежуточных членов твердого раствора цепинит-Na–«цепинит-Ba»–цепинит-K, которые характеризуются высокой степенью гидратации и низким содержанием внекаркасных катионов. Параметры моноклинных ячеек: a = 14.5086(6), b = 14.2174(6), c = 7.8712(3) Å, β = 117.119(4)°, V = 1444.09(11) Å3 (образец 1) и a = 14.2582(4), b = 13.7541(6), c = 7.7770(2) Å, β = 116.893(4)°, V = 1360.20(9) Å3 (образец 2). Кристаллохимические формулы (Z = 2): |A[Na0.84K0.6[(H2O)4]5.2]BK0.2CBa0.25D[Ca0.35Na0.15Fe0.025(H2O)]|{M1(Ti1.2Nb0.8)M2(Ti1.1Nb0.9)(O,OH)4(Si4O12)2} для образца 1 и |A[Na1.6(H2O,H3O)0.4]BK2C(Ba0.51Sr0.21)D[Mn0.3Ca0.2(H2O)](H2O)4|{M1(Ti1.94Nb0.06)M2(Ti1.88Nb0.12)(O,OH)4(Si4O12)2} для образца 2. Высокая степень гидратации образца 1 выражается в присутствии гидратных комплексов протона, а также тетраэдрических [H2O]4-ассоциатов. Для минералов группы лабунцовита характерен так называемый «блочный изоморфизм» связанные с различным распределением D-катионов. Проведенный нами анализ гетерополиэдрических МТ-каркасов в МГЛ позволил установить топологические особенности катионных сеток.

A potentially new mineral—structural analog of magnesiohögbomite-2N3S (Mg,Ti)8Al20O38(O,OH)2, containing Zn, Fe, Sb, and Mn as species-defining components, has been studied using electron-probe and X-ray diffraction analysis. The diffraction experiment was performed on a crystal presenting an aggregate of högbomite and nezilovite with close unit-cell parameters. The trigonal-cell parameters for the studied mineral are a = 5.8805(3) Å, c = 23.077(8) Å, V = 691.50(3) Å3, sp. gr. P 3̅ m1. The structural model was refined using a limited number of unique reflections (1165 reflections with F > 4σ(F)) to R = 0.068. The simplified formula Zn8(Mn2+,Mn3+)2Mg2(Sb0.65Mn _0.35^2 + )(Fe _5^3 + Sb1.0)(Fe _4.5^3 + Sb1.5)Al3O37(О,OН)3 (Z = 1) corresponds to the empirical one. The found distribution of cations over structural model sites is confirmed by the local charge balance. The mineral structure is based on layers of edge-sharing Fe3+ and Al octahedra. These layers alternate with heteropolyhedral layers of Zn tetrahedra, which combine octahedra centered by (Sb,Mn), Mn, and Mg.

Research subject . The crystal structure of christofschäferite-(Ce) was previously refined in terms of the P 2 1 / m low-symmetrical space group, which allowed the local features of cationic arrangements to be determined. In this work, we set out to refine the crystal structure of christofschäferite-(Ce) in terms of the P 2 1 / a high-symmetrical space group based on the previously collected diffraction data. A topology-symmetrical analysis of the members of the chevkinite group with the general formula of A 4 BC 2 D 2 (Si 2 O 7 ) 2 O 8 was conducted. Materials and methods . A magmatic rock sample with christofschäferite-(Ce) inclusions was found in the vicinity of the Laacher See volcano, near Mendig, Eifel Mountains, Rhineland-Palatinate (Rheinland-Pfalz), Germany. The crystal structure was studied using single-crystal X-ray analysis. Results . Despite an increase in the symmetry to the P 2 1 / a space group (in comparison with the previous data with the P 2 1 / m space group), the main patterns of cation distribution between the octahedral and tetrahedral sites are preserved. However, due to the lover number of cationic sites, this distribution becomes more disordered. Based on a crystal chemical analysis of the crystal structures of natural and synthetic members of the chevkinite group in the framework of the OD theory, it is possible to combine them into a united OD family with the same OD groupoid. Conclusions . According to the OD theory, there are two structural OD-subgroups of the chevkinite group (chevkinite and perrierite). The crystal structure and symmetry of possible MDO-polytypes are predicted.

The crystal structure of a potentially new member of the eudialyte group, the Nb-deficient analogue of oneillite from Mont Saint-Hilaire, Québec, Canada, with the idealized formula: Na13(Ca3Mn3)Zr3(Fe,Mn)3(,Nb)(Si,Nb,) [Si3O9]2[Si9O27]2(O,OH,Cl)3•2H2O, has been re-studied within the space group P3. The unit-cell parameters are: a = 14.134(3), c = 30.178(6) Å, V = 52201 Å3. The crystal structure of the mineral has been previously investigated using the space group R3 (typical for the members of oneillite family). In this work a structural model characterized by 155 crystallographic sites was solved in the frame of the low symmetry space group P3 and refined to R = 5.9 % using 4179 reflections with F > 2(F). The cation distribution between the key sites in low symmetry is more detailed.

The modular approach is a powerful tool in current inorganic crystal chemistry. It enables not only a more detailed analysis of the known structures and the determination of structural relationships between them, but also the prediction of potentially novel structures that can be applied in modern materials science. A large number of examples of compounds with modular structures allows us to state that structural modularity is a widely spread phenomenon among natural and synthetic compounds. The use of the formalism of OD theory makes it possible to analyze the symmetry of polytypes with different crystal structures. In this review, we collected new data published in the last 15 years about OD structures and phenomena of polytypism and modularity in inorganic compounds, as well as the topological approach to the analysis of crystal structures.

The chemical composition, crystal structure, and characteristics of the Raman spectrum of a highly hydrated aqualite-like mineral of the eudialyte group from the Kovdor massif (Kola Peninsula, Russia), in which potassium and hydronium group H 3 O + are the species-defining extraframework cations, are studied. The simplified formula of the mineral is (H 3 O) 8 Na 5 K 2 Zr 3 Ca 6 [Si 24 O 69 (OH) 3 ][Si 2 ]Mn(OH) 2 Cl·2H 2 O. It is characterized by space group R 3 and unit-cell parameters a = 14.184(1), c = 30.797(1) Å, V = 5366.27(1) Å 3 . A specific feature of this mineral, which distinguishes it from all other representatives of the eudialyte group, is a high degree of order in the distribution of large extraframework cations (Na + , K + , Sr 2+ , Ba 2+ , Ln 3+ , and H 3 O + ) over split sites of the crystal structure. In the studied mineral, some oxonium ions form complexes with water molecules with extremely strong hydrogen bonds similar to those that are realized in proton hydrate complexes such as Zundel and Eigen cations.

The structure of a new eudialyte-group mineral sergevanite has been investigated using X-ray diffraction (XRD) analysis and electron probe microanalysis. The parameters of an elementary trigonal cell of the mineral are found to be a = 14.2179(1) Å, c = 30.3492(3) Å, and V = 5313.1(7) Å3; sp. gr. R3. The crystal structure is refined to the final reliability factor R = 2.74

A variety of the mineral nezilovite, containing antimony and an elevated amount of titanium, has been studied using microprobe and X-ray diffraction analysis. The diffraction experiment was performed on a crystal presenting an aggregate of nezilovite and högbomite with close unit-cell parameters. The parameters of the hexagonal cell of the nezilovite studied are a = 5.8855(2) Å, c = 23.092(1) Å, V = 692.73 (4) Å3,sp. gr. P63/mmc. The structural model is refined using a limited number of unique reflections 231F 4σ(F) to R = 0.08. The crystallochemical formula is (Z = 2) PbZn2(Ti0.9Al0.1)(Al0.6Sb )Mn Fe O18.5(O,OH)0.5. The distribution of cations of this composition over structure sites is established. A basis of the mineral structure is a set of spinel layers, consisting of edge-sharing Fe3+ octahedra. They alternate with two heteropolyhedral layers: Zn tetrahedra combine (Al,Sb) octahedra in one layer, and five-vertex Ti polyhedra combine dimers of Mn3+ octahedra in the other layer.