The new mineral polyarsite, ideally Na7CaMgCu2(AsO4)(4)F2Cl, was discovered in high-temperature incrustations of the active Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. It is associated with aegirine, sanidine, ferrisanidine, hematite, halite, sylvite, cassiterite, evseevite, axelite, badalovite, johillerite, arsmirandite, aphthitalite, tridymite, potassic-magnesio-fluoro-arfvedsonite and litidionite. Polyarsite forms short-prismatic, equant or tabular crystals up to 0.15 mm across, their clusters up to 0.3 mm in size or crusts up to 0.5 mm across and up to 0.03 mm thick. Polyarsite is transparent, sky-blue to light blue, with vitreous lustre. It is brittle, no cleavage is observed and the fracture is uneven. Dcalc. = 3.592 g cm-3. Polyarsite is optically biaxial (+), alpha = 1.624 (4), beta = 1.645 (4), gamma = 1.682 (4) (589 nm), 2V(meas.) = 70 (10)degrees. The empirical chemical formula calculated based on 19 O+F+Cl apfu is Na7.04Ca1.00Mg0.92Cu2.06Fe0.063+(As3.96S0.05)(Sigma 4.01)O16.28F1.66Cl1.06. Polyarsite is monoclinic, space group I2/m, a = 8.4323(4), b = 10.0974(4), c = 10.7099(6) angstrom, beta = 90.822(4)degrees, V = 911.79(8) angstrom(3) and Z = 2. The crystal structure was determined based on SCXRD data, R = 0.0391. Polyarsite demonstrates a novel structure type. The structure is based on the (1 0 1) heteropolyhedral layers formed by Cu2O8Cl dimers built by CuO4Cl tetragonal pyramids sharing common Cl vertex, AsO4 tetrahedra and MgO4F2 octahedra. Adjacent layers are linked via CaO8 cubes to form a pseudo-framework which hosts octahedrally coordinated Na cations. Polyarsite was named based on the Greek words pi omicron lambda upsilon sigma, poly, "many" and due to belonging to arsenates: this arsenate contains many chemical components ordered between different positions in crystal structure.

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).

Sulfur-enriched sodalite-group feldspathoids from the Lovozero alkaline complex (Kola Peninsula, Russia) and products of their laboratory, anthropogene, and natural thermal and radiation-induced transformations have been studied by electron-probe nicroanalysis, single-crystal X-ray diffractometry, Raman, infrared, and electron spin resonance spectroscopy, and ultra-violate, visible, and near-infrared absorption spectroscopy. Sodalite Na8[Al6Si6O24]Cl2 and sapozhnikovite Na8[Al6Si6O24](HS)2 form an almost continuous, isomorphous series in highly agpaitic feldspathoid syenites and their pegmatites with the Cl : HS ratio ranging from Cl100(HS)0 to Cl12(HS)88 (mol S_2^∙ - radical anion (500–600°C) and, then, the S_3^∙ - radical anion (700°C and higher). The S_3^∙ - groups also appear at the radiation-induced transformation of these minerals. Under the natural radioactive irradiation, at the contact with Th-enriched steenstrupine, an intermediate member of the sodalite–sapozhnikovite series transformed to the S_3^∙ - rich sodalite variety with the simplified formula Na8[Al6Si6O24][Cl,(S3)] earlier unknown in nature.

The new alluaudite-group mineral manganobadalovite (IMA 2020-035), ideally NaNaMn(MgFe3+)(AsO4)3, was found in the Arsenatnaya fumarole, the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption 1975-1976, Tolbachik volcano, Kamchatka peninsula, Far-Eastern Region, Russia. Manganobadalovite is a fumarolic mineral, and its aggregates are found overgrowing basalt scoria or exhalative hematite crystal crusts. Associated minerals are badalovite, hematite, cassiterite, sanidine, glauberite and metath & eacute;nardite. Manganobadalovite occurs as prismatic to equant crystals up to 0.8 mm long typically combined in open-work clusters; it also forms grains that are irregular in shape and cavernous granular crusts up to 0.5 cm. The mineral is transparent, with vitreous luster, and its color varies from red to yellow. Manganobadalovite is brittle and has a noticeable cleavage in one direction and uneven fracture. The calculated density is 4.108 g cm-3. Manganobadalovite is optically biaxial (+), alpha = 1.790 (7), beta = 1.800 (7), gamma = 1.815 (8) and 2Vmeas = 80 (5)degrees. Chemical composition (wt.%, electron-microprobe): Na2O 8.75, K2O 0.17, MgO 5.32, CaO 3.68, MnO 10.09, CuO 0.42, Al2O3 0.18, Fe2O3 13.90, V2O5 0.42, As2O5 56.75, total 99.68. The empirical formula calculated based on 12 O apfu is Na1.69K0.02Ca0.39Mn0.85Mg0.79Cu0.03Fe3+1.04Al0.02(As2.96V0.03)& sum;2.99O12. The crystal structure was solved using single-crystal XRD data, R = 2.30%. Manganobadalovite is monoclinic, C2/c, a = 12.1848(5), b = 12.8924(4), c = 6.6970(3) & Aring;, beta = 113.113(5)degrees, V = 967.60(7) & Aring;3 and Z = 4. The strongest reflections of the powder XRD pattern are [d,& Aring;(I)(hkl)]: 6.43(30)020, 3.589(32)(-131, 310), 3.215(38)(040, -112), 3.079(23)(221, 002), 2.941(32)(-312, -222, -331), 2.852(15)(041), 2.788(100)(330, 400, 240, 022), 2.649(22)(-402, 112), 2.626(25)(-132). Manganobadalovite is named as an analogue of badalovite NaNaMg(MgFe3+)(AsO4)3 with Mn2+ prevailing in the M(1) site.

New niobium lithium 1M mica germanate-silicate KNb(Li0.9Nb0.02 square 0.08)2[(Ge0.4Si0.6)4O10]O2 was synthesized hydrothermally at temperature 280-290 degrees C and a pressure 80-100 atm. It crystallises in the polar C2 space group. The simultaneous inclusion of lithium and niobium was achieved for the first time in the structure, and the presence of octahedral lithium was confirmed by Raman spectroscopy. The trioctahedral central layer possesses one octahedron fully occupied by Nb and two octahedra statistically occupied predominantly by Li with a small Nb impurity and vacancy. Ge-Si isomorphic substitution was revealed in tetrahedra, which made it possible to implement the inclusion of large Nb in the structure compared to conventional micas. The presence of disordered octahedral positions and isomorphism indicates structural defects overall. Between 1M, 2M, 2O, and 3T polytypes in the mica family, topology-symmetry analysis allowed us to find the origin of existence of the 1M or 2M (2O) polytypes based on the symmetry of heteropolyhedral octahedra and tetrahedra packets and symmetry operation of their multiplication in the structures. Under Nd:YAG laser illumination, powders of polar Nb-mica demonstrate second harmonic generation (SHG) with output as high as 20 compared to alpha-quartz powder but only 0.1 to LiNbO3. Despite lower Nb concentration in lithium niobium 1M mica germanate-silicate, the structure-property relation here is similar to LiNbO3, being determined by shortened bonds in the distorted Nb-O octahedron directed along the polar axis.

The sulfide-free metasomatic rocks with chalcophile metals from the Ne & zcaron;ilovo ore field, near Veles, Republic of North Macedonia belong to a rare kind of ore. The mineralogy and petrology of these rocks were studied in detail and can be considered as a standard description for ores of this type. A characteristic feature of Ne & zcaron;ilovo-type ores is a wide variety of accessory oxide minerals containing chalcophile elements (Zn, Pb, Sb, Cu and As). The new nolanite-supergroup mineral zincorinmanite-(Zn), ideally (Fe3+2Zn)SbZnO7(OH), was discovered in the Ne & zcaron;ilovo ore. The associated minerals are quartz, baryte, gahnite, Zn-bearing phlogopite, together with accessory hematite, almeidaite, a Pb-analogue of hydroxycalciorom & eacute;ite and an insufficiently studied Sb-rich h & ouml;gbomite-supergroup mineral. Zincorinmanite-(Zn) forms lamellar to tabular subhedral single-crystal grains up to 0.5 mm across and up to 40 mu m thick. The colour and streak are black and the lustre is submetallic. The new mineral is brittle, with the Mohs' hardness of 6. No cleavage is observed. The fracture is uneven. The calculated density is 5.446 gcm-3. In reflected light, zincorinmanite-(Zn) is light grey, no pleochroism is observed. The reflectance values (Rmin, %/Rmax, %/lambda, nm) are: 12.6/13.7/470, 12.1/13.2/546, 11.8/12.8/589 and 11.5/12.2/650. The Raman spectrum shows bands corresponding to the O-H and Sb-O stretching vibrations and (Fe3+,M2+)-O-H bending modes. The chemical composition is (electron microprobe data, with iron divided into Fe2O3 and FeO based on the charge balance and H2O calculated from the structural data, wt.%): MgO 1.42, MnO 0.44, FeO 2.04, ZnO 22.55, Al2O3 1.95, Fe2O3 35.59, TiO2 1.51, Sb2O5 33.05, H2O 1.18, total 99.73. The empirical formula is [(Fe3+2.12Al0.18)(Zn0.32Mg0.16Fe2+0.13Mn0.03)Ti0.06]Sigma 3.00(Sb0.97Ti0.03)Sigma 1.00Zn1.00O7[(OH)0.61O0.39]Sigma 1.00. The crystal structure was determined using single-crystal X-ray diffraction data and refined to R = 0.0191. Zincorinmanite-(Zn) is hexagonal, space group P63mc, a = 5.9720(1), c = 9.3578(1) & Aring; and V = 289.031(8) & Aring;3 (Z = 2). The new mineral is isostructural with other members of the nolanite group. The strongest lines of the powder X-ray diffraction pattern [d, & Aring; (I, %) - hkl] are: 5.176 (46) - 100; 3.473 (77) - 102; 2.989 (46) - 110; 2.674 (86) - 103; 2.520 (100) - 112; and 2.496 (42) - 201.

New Li,Nb–mica 1M structure KNb(Li 0.9 Nb 0.02 □ 0.08 ) 2 [(Ge 0.4 Si 0.6 ) 4 O 10 ]O 2 .

The new ixiolite-group mineral nioboixiolite-(Fe3+), ideally (Nb0.5Fe0.53+)O-2, was discovered in nosean sanidinite of the Laach Lake (Laacher See) volcano, Eifel region, Rhineland-Palatinate, Germany. The associated minerals are sanidine, K-bearing albite, nosean, biotite, Nb-rich ilmenite, Ti-rich magnetite, hercynite, corundum, samarskite-(Y), ekebergite and columbite-(Fe). Nioboixiolite-(Fe3+) forms long prismatic to acicular crystals up to 0.03 x 0.06 x 1 mm and epitaxial intergrowths with ilmenite and intermediate members of the samarskite-ekebergite series. Both colour and streak are black and the lustre is submetallic. The new mineral is brittle, with the Vickers' micro-indentation hardness of 499 kg mm(-2) which corresponds to the Mohs' hardness of 5. No cleavage is observed. The fracture is conchoidal. The calculated density is 5.033 gcm(-3.) In reflected light, nioboixiolite-(Fe3+) is grey, no pleochroism is observed. The reflectance values (R-min, %/R(ma)x, %/lambda, nm) are: 14.7/16.4/470, 14.3/15.9/546, 14.1/15.7/589 and 14.0/15.8/650. The Raman spectrum shows bands corresponding to stretching vibrations of (Nb,Ti)-O-(Nb,Ti) and (Nb,Ti)-O-Mn(2+ )and the absence of bands of OH groups. The chemical composition is (electron microprobe data, wt.%): MgO 0.41, MnO 3.52, Al2O3 0.42, Cr2O3 0.75, Fe2O3 20.23, TiO2 22.26, ZrO2 0.76, Nb2O5 51.82, total 100.17. The empirical formula is (Mg0.04M0.20n2+)Sigma(0.24)((AlCr0.04Fe1.013+)-Cr-0.03)Sigma(1.08)(Ti1.11Zr0.02)Sigma 1.13Nb1.55O8 (Z = 1). The strongest lines of the powder X-ray diffraction pattern [d, & Aring; (I, %) (hkl)] are: 3.586 (29) (110), 2.917 (100) (111), 2.503 (18) (002), 2.170 (18) (121), 1.738 (22) (130), 1.689 (26) (221). The crystal structure was determined using single-crystal X-ray diffraction data and refined to R = 0.0447. Nioboixiolite-(Fe3+) is orthorhombic with space group Pbcn, a = 4.6578(6), b = 5.6230(7), c = 5.0182(5) & Aring; and V = 131.43(3) & Aring;(3). The new mineral is isostructural with other members of the ixiolite group.

The new mineral achyrophanite (K,Na)3(Fe3+,Ti,Al,Mg)5O2(AsO4)5 was found in high-temperature sublimates of the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. It is associated with aphthitalite-group sulfates, hematite, alluaudite-group arsenates (badalovite, calciojohillerite, johillerite, nickenichite, hatertite, and khrenovite), ozerovaite, pansnerite, arsenatrotitanite, yurmarinite, svabite, tilasite, katiarsite, yurgensonite, As-bearing sanidine, anhydrite, rutile, cassiterite, and pseudobrookite. Achyrophanite occurs as long-prismatic to acicular or, rarer, tabular crystals up to 0.02 × 0.2 × 1.5 mm, which form parallel, radiating, bush-like, or chaotic aggregates up to 3 mm across. It is transparent, straw-yellow to golden yellow, with strong vitreous luster. The mineral is brittle, with (001) perfect cleavage. Dcalc is 3.814 g cm–3. Achyrophanite is optically biaxial (+), α = 1.823(7), β = 1.840(7), γ = 1.895(7) (589 nm), 2V (meas.) = 60(10)°. Chemical composition (wt.%, electron microprobe) is: Na2O 3.68, K2O 9.32, CaO 0.38, MgO 1.37, MnO 0.08, CuO 0.82, ZnO 0.48, Al2O3 2.09, Fe2O3 20.42, SiO2 0.12, TiO2 7.35, P2O5 0.14, V2O5 0.33, As2O5 51.88, SO3 1.04, and total 99.40. The empirical formula calculated based on 22 O apfu is Na1.29K2.15Ca0.07Mg0.34Mn0.01Cu0.11Zn0.06Al0.44Fe3+2.77Ti1.00Si0.02P0.02S0.14V0.04As4.90O22. Achyrophanite is orthorhombic, space group P2221, a = 6.5824(2), b = 13.2488(4), c = 10.7613(3) Å, V = 938.48(5) Å3 and Z = 2. The strongest reflections of the PXRD pattern [d,Å(I)(hkl)] are 5.615(59)(101), 4.174(42)(022), 3.669(31)(130), 3.148(33)(103), 2.852(43)(141), 2.814(100)(042, 202), 2.689(29)(004), and 2.237(28)(152). The crystal structure of achyrophanite (solved from single-crystal XRD data, R = 4.47%) is unique. It is based on the octahedral-tetrahedral M-T-O pseudo-framework (M = Fe3+ with admixed Ti, Al, Mg, Na; T = As5+). Large-cation A sites (A = K, Na) are located in the channels of the pseudo-framework. The achyrophanite structure can be described as stuffed, with the defect heteropolyhedral pseudo-framework derivative of the orthorhombic Fe3+AsO4 archetype. The mineral is named from the Greek άχυρον, straw, and φαίνομαι, to appear, in allusion to its typical straw-yellow color and long prismatic habit of crystals.

A multimethodic approach based on infrared, Raman, electron spin resonance and photoluminescence spectroscopy, absorption spectroscopy in near infrared, visible and ultraviolet regions, single-crystal X-ray diffraction as well as electron microprobe analyses was applied to the characterization of a new commensurately modulated cubic haüyne analogue with the modulation parameter of 0.2 and unit-cell parameter of 45.3629(3) Å (designated as haüyne-45Å) from the Malobystrinskoe lazurite deposit, in the Baikal Lake area, Siberia, Russia, as well as associated SO32−-bearing afghanite. Haüyne-45Å is the second member, after vladimirivanovite, of the sodalite group with a commensurately modulated structure. The average structure is based on the tetrahedral aluminosilicate sodalite-type framework with sodalite cages of different sizes. The simplified formula of haüyne-45Å is Na6Ca2−x(Si6Al6O24)(SO42−,HS−,S2●−,S4,S3●−,S52−)2−y. The structural modulations of the haüyne-45Å framework are presumably related to the regular alternation of SO42− anions with polysulfide S2●−, S3●−, S4, and S52− groups detected by the spectroscopic methods. Mechanisms of thermal conversions of S-bearing groups in haüyne-45Å under oxidizing and reducing conditions at temperatures up to 800 °C are studied, and their geochemical importance is discussed.

The paper reports the first comprehensive physicochemical study of minerals of the amblygonite LiAlPO4F–montebrasite LiAlPO4(OH) series. An EPR spectroscopic and calorimetric study of montebrasite LiAlPO4(OH)0.9F0.1 from the Shuk-Byul rare-metal granite pegmatites (Sangilen Highlands, Tuva) and amblygonite LiAlPO4F0.5(OH)0.5 from pegmatites of the Voron’i Tundras (Kola Peninsula) was carried out. Using the EPR method, the radiation-sensitive paramagnetic O– centers were discovered. They were formed without participation of impurity elements in the regular sites of crystal lattice. The possibility use of minerals of the amblygonite–montebrasite series for EPR geochronometry has been demonstrated for the first time. Using the method of high-temperature melt dissolution calorimetry on a Tian-Calvét microcalorimeter, the enthalpies of formation from elements Δ_fH_el^0 (298.15 K) = –2326.3 ± 2.2 kJ/mol for montebrasite with the composition LiAl(PO4)(OH)0.9F0.1 and for amblygonite with the composition LiAl(PO4)F0.5(OH)0.5 (‒2347.9 ± 3.1 kJ/mol) are obtained; and the values of this parameter are calculated for the end members with an ideal composition of the series: for montebrasite (–2315.5 ± 2.2 kJ/mol) and for amblygonite (–2401.6 ± 3.1 kJ/mol). The values of the standard entropy S0 (298.15 K) and the Gibbs energy of formation Δ_fG_el^0 (298.15 K) for intermediate and end members of the amblygonite–montebrasite series are estimated.

New data on the crystal structure, chemical composition, and nature of extra-framework components of the orthorhombic sodalite-group mineral vladimirivanovite were obtained using chemical and single-crystal X-ray diffraction data as well as infrared and Raman spectroscopy. The crystal structure of vladimirivanovite is based on the sodalite-type aluminosilicate framework with ordered Al and Si atoms. Sodalite-like cages are mainly occupied by Na+ and Ca2+ cations and (SO4)2− anions. It was shown that vladimirivanovite is characterized by significant variations in the content of extra-framework polysulfide groups (S3•−, S4), as well as other neutral molecules (H2O and CO2), the presence of which in the structure is the main cause of structural modulations and the orientation disordering of sulfate anions. Three samples with different S3•−:S4 ratios were studied. All of them are orthorhombic (space group Pnaa) with the unit-cell parameters a ≈ 9.1, b ≈ 12.9, and c ≈ 38.6 Å; Z = 6. The general crystal-chemical formula of vladimirivanovite is (Na+6.0–6.4Ca2+1.5–1.7)(Al6Si6O24)(SO42−,S3•−,S4)1.7–1.9(CO2)0–0.1·nH2O (n = 1–3), where the S4 molecule occurs in different conformation states.

The results of the study of the platinum group minerals of the Baimka gold placer cluster, Western Chukotka, Russia, are presented. Platinum group minerals belong to the iridium-platinum and platinum miner- alogical-geochemical types with the Late Jurassic cumulative pyroxenite-gabbro complexes as a probable source. Platinum group minerals came to alluvial gold placers primarily from intermediate reservoirs, which is the Volgian volcanic-sedimentary sequence. Rounded silicate glass inclusions are a specific feature of platinum minerals from the Baimka placer cluster.

New data on the crystal structure and isomorphism of extra-framework components in the cancrinite-group mineral tounkite have been obtained using chemical and single-crystal X-ray diffraction data, as well as infrared, Raman, ESR, UV–Vis–near-IR absorption and photoluminescence spectroscopy methods. The crystal structure of tounkite is based on the aluminosilicate framework formed by the САСАСВСВСАСВ stacking sequence with ordered Si and Al atoms The framework hosts Losod and liottite cages as well as columns of cancrinite cages. It is shown that tounkite is characterized by wide variations of the chemical composition. Its simplified crystal–chemical formula is (Na+3.89–5.18K+0.15–1.64Ca2+2.30–2.58(Al6Si6O24)(SO42−,S52−,S4) 2−x (Cl−, HS−)1+y·nH2O (x, y, n < 1). The S2⦁− and S3⦁− radical anions may occur in some tounkite samples in minor amounts. These crystal–chemical features indicate that tounkite crystallizes under highly reducing conditions. All studied tounkite samples were polysynthetic twins. A large 10-layed cage formed at the border between twin components, connected by a rotation of 180° around the [001] axis, which may host the large S52− anion.

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.

The article describes the results of a comprehensive study of the extra-framework components of scapolites using quantum–chemical calculations, electronic and vibrational spectroscopy, and single-crystal X-ray diffraction and crystal structure refinement. The ab initio calculations were performed using an embedded-cluster approach of extra-framework components in various cation surroundings. As a result, through comparing the experimental and ab initio calculation results, the energies of the electronic and vibrational transitions of various extra-framework components (CO3)2−, (CO3)·−, S3·−, S2·−—as well as the role of these components in the process of the lowering of the symmetry—were determined for scapolites belonging to the marialite–meionite solid–solution series. The nature of the various colors of the scapolites has also been established. Colors from purple to blue are a result of the presence of radiation-induced pairs of defects: carbonate radical anions (CO3)·− and F-centers. However, polysulfide S3·− radical anions are found in some violet scapolites.

Tourmaline is a widespread borosilicate mineral that is well known for its variable chemistry. Although a major amount of octahedral Al in tourmaline is commonplace, the occurrence of significant amounts of tetrahedral Al is relatively rare. This paper focuses on tourmaline from the collection of the A.E. Fersman Mineralogical Museum (Russia) originated from Italy with up to 25% of Si replaced by Al at the tetrahedral site. The tourmaline is characterized by optical and scanning electron microscopy, Raman spectroscopy, infrared spectroscopy, M & ouml;ssbauer spectroscopy, energy-dispersive and wavelength-dispersive X-ray analysis, laser ablation inductively coupled plasma optical emission spectrometry and single-crystal X-ray diffraction. The studied tourmaline occurs as transparent dark blue crystals (with equant external morphology) up to 3 mm in size and forms veinlets cutting a (Mg,Al)-rich metamorphosed mafic-ultramafic rock (Mg >> Fe) composed of spinel, pargasite, clinochlore, phlogopite, and hydroxylapatite. The studied tourmaline meets the criteria defining magnesio-lucchesiite and can be compositionally formed via Tschermak-like (Me-[6](2+) + Si-[4](4+) <-> Al-[6](3+) + Al-[4](3+), where Me-[6](2+) = Mg,Fe) or plagioclase-like (Ca-[9](2+) + Al-[4](3+) <-> Na-[9](+) + Si-[4](4+)) substitutions. Zones with a relatively high Si content (Si-rich) have pronounced indications of dissolution, while silicon-depleted zones (Si-poor) overgrow Si-rich zones, eventually creating a visible replacement zone of the crystal. We suggest that Si-poor tourmaline results from the Si-rich tourmaline losing Si during a metasomatic process. The resulting empirical crystal-chemical formula for the Si-poor zone is: (X)(Ca(0.95)Na(0.03)y(0.02))(Sigma 1.00)(Y)(Mg-1.08 Al(0.98)Fe0.502+Fe0.433+)(Sigma 3.00)(Z)(Al(5.91)Fe0.093+)(Sigma 6.00)(T)[(Si4.57Al1.43)(Sigma 6.00)O-18] (BO3)(3)(V)(OH)(3)(W)[O-0.95(OH)(0.05)](Sigma 1.00) [a = 15.9811(2), c = 7.12520(10) angstrom, R1 = 1.7%] and for the Si-rich zone is: (X)(Ca0.89Na0.11)(Sigma 1.00)(Y)(Mg(1.55)Al(0.80)Fe0.342+Fe0.313+)(Sigma 3.00)(Z)(Al(5.51)Mg(0.44)Fe0.053+)(Sigma 6.00)(T)[(Si5.35Al0.65)(Sigma 6.00)O-18] (BO3)(3)(V)(OH)(3)(W)[O-0.93(OH)(0.07)](Sigma 1.00) [a = 15.9621(3), c = 7.14110(10) angstrom, R1 = 1.7%]. According to pressure-temperature (P-T) calculations of mineral assemblage stability and comparable data on synthetic Al-[4]-rich tourmalines, the studied tourmaline was formed at 600-750 degrees C and 0.10-0.20 GPa. The formation of tetrahedral Al-rich tourmalines requires several unusual factors: (1) desilication of primary rocks and (2) high temperatures and relatively low pressures.