Abstract A new organically templated hybrid organo-inorganic compound, (C 4 H 12 N 2 )SO 4 ⋅3H 2 SeO 3 , was prepared during systematic studies of sulfate co-crystals with selenious acid. The new compound crystallizes in a non-centrosymmetric space group P 2 1 ( a = 6.2876(2) Å, b = 17.9296(6) Å, c = 7.2701(3) Å, β = 106.979(4)°, R 1 = 0.027) and exhibits a weak SHG activity. The new compound belongs to a rapidly developing family of hydrogen-bonded architectures formed by selenious acid co-crystals. The crystal structure corresponds to a pseudo-layered hydrogen-bonded framework with alternating organic and inorganic “slabs” linked by hydrogen bonds.

Hydrated sodium and magnesium sulfates are fairly common minerals. This study is focused on l & ouml;weite from the fumaroles of the Tolbachik volcano in Kamchatka. The crystal structure of l & ouml;weite was refined using single-crystal X-ray diffraction, and the hydrogen atoms were localized for the first time. In situ single-crystal (temperature range -173 to 227 degrees C) and powder (temperature range -173 to 900 degrees C) X-ray studies were performed. Both techniques show that l & ouml;weite remains stable up to similar to 220 degrees C without showing any signs of potential phase transitions. The mineral is also stable under a vacuum of similar to 600 Pa. The following transformation sequence for l & ouml;weite was observed upon heating: l & ouml;weite -> metath & eacute;nardite + vanthoffite + 'x-phase' -> metath & eacute;nardite + periclase.The thermal expansion of l & ouml;weite demonstrates two distinct patterns in two temperature ranges. There is virtually no expansion in the structure until -93 degrees C. Following this, the structure rapidly expands, exhibiting a highly anisotropic behaviour. Shear deformations of the soft S-O-Mg and S-O-Na hinges explain the structural flexibility and adaptability of l & ouml;weite to changes in physicochemical environments.

Crystals of two new alkaline-earth perrhenate halides, Sr(ReO4)Br⋅2H2O (1) and Ba(ReO4)I⋅2H2O (2) were obtained upon evaporation of aqueous solutions at 95 – 100 °C. Both compounds are isostructural to the previously reported Ca(ReO4)Cl⋅2H2O and crystallize in orthorhombic symmetry with the space group Cmcm (a = 7.3906(5) Å, b = 14.241(1) Å, c = 7.1032(5) Å for 1 and a = 7.8624(4) Å, b = 14.0202(5) Å, c = 7.7190(3) Å for 2). Both structures can be regarded as pseudo-layered 3D frameworks comprised of AO8X capped square antiprisms (A = Sr, Ba; X = Br, I) and ReO4 tetrahedra which share vertices with formation of slightly distorted tetragonal pseudo-layers linked by OH⋅⋅⋅X hydrogen bonds. The cationic centers (alkaline earths and rhenium) adopt a litharge-like arrangement. The structure seems to be very sensitive to the ratio of A2+ and X− constituents; it is as yet observed with calcium, only as a chloride, with strontium, only as a bromide, and with barium, only as an iodide.

Copiapite-group minerals are among the most common hydrated iron sulfate minerals in a variety of geological environments on Earth. They are also believed to be widespread on the Martian surface. The transformation and stability of the copiapite-group minerals are examined in this study using a diverse array of methods, including low- (LT) and high-temperature (HT) single-crystal X-ray diffraction (SCXRD), LT- and HT-powder X-ray diffraction (PXRD), vacuum powder X-ray diffraction, HT-Raman spectroscopy, magnetization and heat capacity measurements. The research is conducted over a broad temperature range (−175–740 °C) and under vacuum (∼ 600 Pa) conditions that are partially similar to those found on the Martian surface (from −153 °C to over 20 °C and ∼ 600 Pa). The obtained results indicate that aluminocopiapite, (Al0.54Fe3+0.13)Σ0.67Fe3+4(SO4)6(OH)2(H2O)20, is unstable under low vacuum conditions and undergoes a structural transition to a post-aluminocopiapite phase, (Al0.63Fe3+0.04)Σ0.67Fe3+4(SO4)6(OH)2(H2O)12.44, with a significantly lower water and iron content and a higher aluminum content. Schwertmannite, Fe3+16O16(OH)9.6(SO4)3.2·10H2O is formed as a film/shell on the crystal surface of post-aluminocopiapite via a single crystal-to-single crystal (SC-SC) topotactic transformation and exsolution. After 14 days of exposure to air, the post-aluminocopiapite crystal with schwertmannite shell undergoes a reversible process, reverting to its initial aluminocopiapite state. A closely analogous transformation, involving partial dehydration, was observed for copiapite, Fe2+Fe3+4(SO4)6(OH)2(H2O)20, demonstrating that this behavior is a general feature of the copiapite group.It is therefore unlikely that copiapite-group minerals would exist on the surface of Mars and in comparable extraterrestrial environments in their initial form. Instead, under Mars surface conditions with low vacuum, post-copiapites and schwertmannite may be among the most common minerals in hydrated iron sulfate mineral associations. This is relevant for decoding past geo- and climatic environments on Mars and for selecting the conditions for the return of intact samples collected by rovers to Earth.

Karlditmarite (IMA 2021-003), Cu9O4(PO4)2(SO4)2, is a new mineral species from an active Arsenatnaya fumarole, Tolbachik volcano, Kamchatka peninsula, Russia.Karlditmarite occurs as green prismatic crystals. The mineral is biaxial (-), with alpha = 1.872(2)degrees, beta = 1.835(3)degrees, and gamma = 1.810(3)degrees (589 nm). Under the microscope, karlditmarite is green with weak pleochroism. Electron microprobe analysis provided the empirical formula (Cu8.614Zn0.175Al0.053Ca0.019Fe0.157)(P1.574S1.814As0.444V0.109Si0.059)O20. Karlditmarite is triclinic, P1: a = 6.1256(7) & Aring;, b = 7.9192(8) & Aring;, c = 7.9866(8) & Aring;, alpha = 75.173(2)degrees, beta = 86.639(2)degrees, gamma = 88.660(2)degrees, V = 373.87(7) & Aring;3. The crystal structure (R1 = 0.039) is unique. The infinity 2Cu9O410+ ${ }_{\infty}<^>{2}\left[\mathrm{Cu}_{9} \mathrm{O}_{4} ight]<^>{10+}$ layer in karlditmarite can be described as composed of six-membered rings, in which two of the six OCu4 tetrahedra share a common edge. The interlayer space between the bends of the highly corrugated infinity 2Cu9O410+ ${ }_{\infty}<^>{2}\left[\mathrm{Cu}_{9} \mathrm{O}_{4} ight]<^>{10+}$ layers hosts phosphate tetrahedra, whereas sulfate tetrahedra are situated above the centers of the rings. Karlditmarite is the first anhydrous Cu phosphate-sulfate mineral among more than 100 copper oxysalt mineral species known from the active fumaroles. In addition, phosphorus geochemistry in fumarolic environments is discussed here.

We introduce Bi_2CuO_3(SO_4) as a rare example of a spin-ladder magnet with ferromagnetic interactions on the rungs. Its magnetic response is studied through measurements of heat capacity, temperature-dependent magnetic susceptibility, and field-dependent magnetization, as well as electron spin resonance spectroscopy. These experiments are complemented by density-functional-theory calculations combined with the construction of maximally localized Wannier functions and an analysis of the relevant superexchange pathways. Quantum Monte Carlo simulations are employed to model thermodynamic properties and to quantitatively determine the magnetic exchange parameters. Our combined approach identifies Bi_2CuO_3(SO_4) as a two-leg spin-ladder system with ferromagnetic rungs (J' ≈ -208 K) and antiferromagnetic legs (J ≈ 258 K). These interactions of similar magnitude arise from remarkably different superexchange pathways, with the Cu–Cu distance along the leg being almost twice as long than the respective distance along the rung. The antiferromagnetic leg coupling represents the strongest oxygen-mediated long-range superexchange in a Cu^2+ compound reported to date and sets the benchmark for the role of complex superexchange pathways in quantum magnets.

Hydrated iron sulfate minerals have received considerable attention from the standpoint of environmental science, as well as due to extensive studies on the mineralogy of Mars. In this paper, we report on the thermal evolution of coquimbite AlFe33+SO46H2O12 center dot 6H2O by single-crystal X-ray diffraction (SCXRD) from -173 to 77 degrees C. Powder X-ray diffraction (PXRD) was performed in the temperature range of -180 to 740 degrees C and low vacuum of 600 Pa. Magnetic properties for coquimbite are reported in the range of -271 to 7 degrees C. It was observed that coquimbite is stable between -180 and + 145 degrees C and at a low vacuum of 600 Pa. We observed a gradual transition from coquimbite to the amorphous phase at 150 degrees C, followed by a transition to mikasaite at 225 degrees C, and a second amorphization at 575 degrees C, with afterward crystallization to hematite. SCXRD shows that the behavior of coquimbite with increasing temperature can be divided into two stages, with negative and strongly anisotropic thermal expansion at Stage I (-173 to -143 degrees C) and only positive thermal expansion at Stage II (-133 to 77 degrees C). All the O-H center dot center dot center dot O bonds remain virtually intact during Stage I, except for Ow2-H3 center dot center dot center dot O2. The negative thermal expansion observed along the c-axis in the LT range is a result of the simultaneous reduction of several bond lengths and angular distortions: (1) decrease of Ow2-H3 center dot center dot center dot O2 hydrogen bonds oriented approximately along the c-axis; and (2) shrinkage of M3O3(H2O)3 octahedra, evidenced by the decrease in M3-O3 and M3-Ow3 bonds. The nature of the expansion of the coquimbite structure during Stage II is better understood in terms of the orientation of [M2M32(SO4)6(H2O)6]3- clusters along the c-axis. M-O and S-O bonds are only slightly affected by the temperature rise at Stage II, whereas O-H center dot center dot center dot O angular transformations seem to be the main driving force for the expansion of the coquimbite structure along the alpha 11 direction upon heating.Coquimbite exhibits distinct magnetic properties compared to other iron sulfates, driven by antiferromagnetic interactions within its M3-M2-M3 trimeric clusters of Fe3+. The presence of Al3+-Fe3+ site mixing in coquimbite introduces structural disorder, partially disrupting its magnetic ordering and contributing to magnetic entropy and magnetization features, such as a 1/3 magnetization plateau.

Thermal expansion of the mineral soddyite, (UO2)2SiO4(H2O)2, and structurally related synthetic compound Na2(UO2)2SiO4F2 ( NAUSIF ) has been studied by means of high-temperature single-crystal and powder X-ray diffraction. The mineral is orthorhombic, Fddd, while NAUSIF is tetragonal, I41/amd. The framework structures of both compounds are comprised of either neutral [(UO2)2(SiO4)(H2O)2] or negatively charged [(UO2)2(SiO4)F2]2- chains of similar topology. In the structure of soddyite, the chains cross at the angle of 72 degrees, while in NAUSIF of 90 degrees. Upon increasing temperature, the acute inter-chain angles in soddyite increase due to hinge deformations, the overall symmetry approaching tetragonal. The mineral is stable below 325 +/- 25 degrees & Scy;; between 325 and 640 degrees & Scy;, the decomposition products cannot be identified unambiguously and contain significant amount of amorphous phases; at higher temperatures, a mixture of U3O8 polymorphs is formed. NAUSIF is stable until its melting point of 625 +/- 25 degrees & Scy;. The thermal expansion of both compounds is strongly anisotropic; for NAUSIF , it is due to difference in bond strength in the uranium and sodium polyhedra. Anisotropic thermal expansion of soddyite is controlled by shear deformations of the structure upon the temperature rise.

Single crystals of two new calcium perrhenates, anhydrous Ca(ReO 4 ) 2 ( 1 ) and K 2 Ca 3 (ReO 4 ) 8 ·4H 2 O ( 2 ), were prepared during solid-state and solution attempts to prepare the potassium analog of NaCa(ReO 4 ) 3 . Both structures can be regarded as frameworks comprised of vertex-sharing CaO 8 and ReO 4 polyhedra. 1 is a complete structural analog of Sr(ReO 4 ) 2 while 2 corresponds to its own structure type. It is also the first hydrated binary perrhenate to date. We discuss the similarities and differences in the structures of alkaline earth perrhenates and pertechnetates; existence of more complex and elegant metal-perrhenate architectures is predicted.

We investigated crystal structures and the mechanism of thermal expansion of weeksite and its synthetic analogues (K-, Rb-, Cs-) using a combination of geometrical-topological analysis and empirical methods (powder X-ray diffraction, infrared spectroscopy, scanning electron microscopy, single-crystal and powder X-ray variable-temperature diffraction). The weeksite sample studied herein was collected at the Anderson mine, Yavapai County, Arizona, USA. Its synthetic analogues were prepared using high-temperature approaches in sealed silica tubes. Natural weeksite is stable up to 860 +/- 10 degrees C; it dehydrates between 100-200 degrees C. Its synthetic analogues with Rb and Cs are stable at least until 1000 degrees C. Their thermal expansion is strongly anisotropic due to shear deformations of the crystal structure. The framework in the structure of weeksite can be regarded as a sequence of uranyl silicate layers linked by SiO4 tetrahedra. With increasing temperature, the angles at the Si-O-Si 'hinges' change, which causes the shear deformations. The differences in the thermal behaviour, including expansion anisotropy, are probably due to the nature (size) of the alkali cations occupying the cavities in the framework. The partial or complete replacement of Rb+ by Cs+ illustrates the zeolite-like nature of the uranyl silicate framework in weeksite. Therefore, its structure can be considered a possible candidate for the selective immobilization of 137Cs+ upon storing nuclear waste with little interference from the more abundant Na+ and K+.

Abstract Kreiterite, CsLi2Fe+3(Si4O10)F2, a new cesium trioctahedral mica was discovered in the Darai-Pioz alkaline massif (Tajikistan). It is named after the Russian geologist, Prof. Vladimir Mikhailovich Kreiter (1897–1966). Kreiterite occurs as lamellar grains or flakes up to 0.2 mm across, irregular in shape and usually slightly deformed, in quartz-pectolite aggregates within so-called “quartz lumps”, the rocks consisting mainly of granular quartz. The mineral is colorless and transparent with vitreous luster. Mohs hardness is 2½, Dmeas. is 3.33(2) g/cm3, and Dcalc. is 3.342 g/cm3. The new mineral is optically biaxial (−) with α = 1.596(2), β = 1.605(2), γ = 1.607(2), 2V(calc) = −50°. It is monoclinic, space group C2/m, C2, or Cm (polytype 1M), a = 5.240(2) Å, b = 9.054(4) Å, c = 10.767(4) Å, β = 99.58(4)°, V = 503.4(6) Å3, and Z = 2. The strongest lines in the powder diffraction pattern are (d Å, I %, hkl): 4.49, 31, (1 1 0); 3.94, 31, (1 1 1); 3.70, 47, ( 1 2), ( 2); 3.45, 36, (0 2 2); 3.00, 34, ( 1 ), ( 3); 2.652, 17, (0 0 4); 2.610, 72, ( 0 1), (1 3 0), ( 3 0); 2.583, 100, (2 0 0), ( 3 1); 2.241, 38, (2 2 0); 2.190, 67, ( 3 3). Chemical analysis by electron microprobe and SIMS (for H2O and Li2O) gave SiO2 47.37, TiO2 0.99, Al2O3 0.29, MgO 0.40, Fe2O3 13.18, ZnO 0.12, K2O 0.02, Cs2O 27.37, Li2O 5.90, H2O 1.28, F 4.77, −O=F −2.01, total 99.68 wt.% The empirical formula, based on 12 (O+F), is Cs0.99Li2.01(Fe3+0.84Ti0.06Mg0.05Al0.03Zn0.01)Σ0.99Si4.01O10(F1.28OH0.72)Σ2. Kreiterite is a ferric-iron analogue of sokolovaite and gorbunovite and the lithium ferric-iron analogue of garmite.

Three new nickel-based representatives of the so-called “layered hydroselenite” family have been characterized by single-crystal X-ray diffraction. In addition to the (enH2)[Ni(HSeO3)2Br2], the last missing member of the ethylenediammonium – transition metal hydroselenite-halide family, we were able to characterize the first members of a new family of compounds based on the N,N′-dimethylethylenediammonium cations, (dmedaH2)[Ni(HSeO3)2X2], X = Cl and Br. We compare the structural peculiarities of layered hydroselenites “stuffed” by the (enH2)2+ and (dmedaH2)2+ cations and predict existence of new series in this peculiar layered family.

In this work, nine new synthetic alkali-and rare-earth metal crichtonite-type compounds withAB3C18O38 general formula are presented. The effect on the magnetic properties as consequence of the substitution of divalent and trivalent cations in the A site, as well as the introduction of iron at the B and C sites is studied. Ferrimagnetic behavior was identified in the crichtonites CaMn3Ti18O38, BaMn3Ti18O38 and CaFe3Ti18O38, which changes to a spin-glass type for the BaMn3Ti14Fe4O38 and A-trivalent REMn3Ti18O38 (RE = La, Ce and Nd), LaFe3Ti18O38 and LaMn3Ti13Fe5O38. A comprehensive comparison of the AC and DC magnetic measurements for whole series along with the FiM structure obtained by neutron powder diffraction is discussed. These results will expand the comprehension on this almost unexplored magnetic family of compounds.

Hydrated iron sulfate minerals have received considerable attention from the standpoint of environmental science, as well as due to extensive studies on the mineralogy of Mars. In this paper, we report on the thermal evolution of coquimbite AlFe33+(SO4)6(H2O)12·6H2O by single-crystal X-ray diffraction (SCXRD) from −173 to 77 °C. Powder X-ray diffraction (PXRD) was performed in the temperature range of −180 to 740 °C and low vacuum of 600 Pa. Magnetic properties for coquimbite are reported in the range of −271 to 7 °C. It was observed that coquimbite is stable between −180 and +145 °C and at a low vacuum of 600 Pa. We observed a gradual transition from coquimbite to the amorphous phase at 150 °C, followed by a transition to mikasaite at 225 °C, and a second amorphization at 575 °C, with afterward crystallization to hematite. SCXRD shows that the behavior of coquimbite with increasing temperature can be divided into two stages, with negative and strongly anisotropic thermal expansion at Stage I (−173 to −143 °C) and only positive thermal expansion at Stage II (−133 to 77 °C). All the O-H···O bonds remain virtually intact during Stage I, except for Ow2-H3···O2. The negative thermal expansion observed along the c-axis in the LT range is a result of the simultaneous reduction of several bond lengths and angular distortions: (1) decrease of Ow2-H3···O2 hydrogen bonds oriented approximately along the c-axis; and (2) shrinkage of M3O3(H2O)3 octahedra, evidenced by the decrease in M3-O3 and M3-Ow3 bonds. The nature of the expansion of the coquimbite structure during Stage II is better understood in terms of the orientation of [M2M32(SO4)6(H2O)6]3− clusters along the c-axis. M-O and S-O bonds are only slightly affected by the temperature rise at Stage II, whereas O-H···O angular transformations seem to be the main driving force for the expansion of the coquimbite structure along the α11 direction upon heating. Coquimbite exhibits distinct magnetic properties compared to other iron sulfates, driven by antiferromagnetic interactions within its M3-M2-M3 trimeric clusters of Fe3+. The presence of Al3+-Fe3+ site mixing in coquimbite introduces structural disorder, partially disrupting its magnetic ordering and contributing to magnetic entropy and magnetization features, such as a 1/3 magnetization plateau.

Новый уранил силикат калия и рубидия (K0.67Rb0.33)2[(UO2)2(Si5O13)](H2O) (1) получен методом синтеза из расплава в вакуумированной кварцевой ампуле. Соединение кристаллизуется в ромбической сингонии, Pbca, a = 14.1909(4), b = 14.0406(5), c = 17.9151(7) Å, V = 3569.6(2) Å3, R1 = 0.03. В кристаллической структуре нового соединения слои [Si5O13]6- объединяются с цепочками из урановых полиэдров с образованием микропористого гетерополиэдрического каркаса, содержащего каналы размером 9.63×3.34 Å, в которых располагаются смешанно-заселенные позиции катионов щелочных металлов. В статье приводится кристаллохимическое сравнение нового соединения со структурами родственных соединений и минералов.

Hydrated iron sulfate minerals receive considerable attention from the standpoint of environmental science, and also due to extensive studies of the mineralogy of Mars. In this paper, we report on the thermal evolution of coquimbite AlFe3+3(SO4)6(H2O)12·6H2O by single-crystal X-ray diffraction (SCXRD) in the range of −173 to 77 °C. Powder X-ray diffraction (PXRD) was performed in the temperature range of −180 to 740 °C and low vacuum of 600 Pa. Magnetic properties for coquimbite are reported in the range of −271 °C to 7 °C. It was observed that coquimbite is stable between −180 °C and +145 °C and low vacuum of 600 Pa. We observed a gradual transition from coquimbite to the amorphous phase at 150 °C, followed by a transition to mikasaite at 225 °C, and a second amorphization at 575 °C, with afterward crystallization to hematite. SCXRD shows that the behavior of coquimbite with increasing temperature can be divided into two stages, with negative and strongly anisotropic thermal expansion at Stage I (−173 to −143 °C) and only positive thermal expansion at Stage II (−133 °C to 77 °C). All the O─H···O bonds remain virtually intact during the Stage I except for Ow2─H3···O2. The negative thermal expansion observed along the c axis in the LT range is a result of the simultaneous reduction of several bond lengths and angular distortions: i) decrease of Ow2─H3···O2 hydrogen bonds oriented approximately along the c axis; ii) shrinkage of M3O3(H2O)3 octahedra evidenced by the decrease in M3─O3 and M3─Ow3 bonds. The nature of the expansion of the coquimbite structure during the Stage II is better understood in terms of the orientation of [M2M32(SO4)6(H2O)6]3− clusters along the c axis. M─O and S─O bonds are only slightly affected by the temperature rise at Stage II, whereas O─H…O angular transformations seem to be the main driving force for the expansion of the coquimbite structure along the α11 direction upon heating. Coquimbite exhibits distinct magnetic properties compared to other iron sulfates, driven by antiferromagnetic interactions within its M3─M2─M3 trimeric clusters of Fe3+. The presence of Al3+─Fe3+ site mixing in coquimbite introduces structural disorder, partially disrupting its magnetic ordering and contributing to magnetic entropy and magnetization features, such as a 1/3 magnetization plateau.

This investigation investigates geologically old, ca. 370 Ma, metamict zirconolite from the Kovdor phoscorites and carbonatites in the Kola Alkaline Province. Mineral composition, crystallisation behaviour, and thermal expansion of the recrystallised samples were analysed using electron microprobe analysis, Raman spectroscopy, and in situ high-temperature powder X-ray diffraction (HTPXRD). The zirconolite crystals investigated are different in their morphology, internal texture, composition, alteration degree, and can be divided into four distinct groups. The zirconolite is a high Nb and Fe3+ variety (10.8-24.1 wt.% Nb2O5 and 7.9-9.0 wt.% Fe2O3), it is enriched in Th (up to 8.7 wt.% ThO2), Ta (up to 5.3 wt.% Ta2O5) and rare earth elements (up to 5.0 wt.% REE2O3). Raman spectroscopy confirmed that metamict zirconolite is anhydrous. The recrystallisation process of the metamict zirconolite is complex, as detected by HTPXRD. A fluorite-type phase starts to crystallise at 420 degrees C. The formation of a pyrochlore phase can be identified at 750 degrees C. The major phases detected in the sample after the recrystallisation are: zirconolite-3T (53 wt.%), srilankite (25 wt.%), pyrochlore (15 wt.%), baddeleyite (5 wt.%) and zircon (3 wt.%). The average coefficients of thermal expansion (CTE) values in the temperature range 25-1200 degrees C are as follows: ${{\bar \alpha }}$a = ${{\bar \alpha }}$b = ${{\bar \alpha }}$11 = ${{\bar \alpha }}$22 = 8.9510-6 deg-1. Similarly, the thermal expansion along the c-axis yields a similar value: ${{\bar \alpha }}$a = ${{\bar \alpha }}$b = 8.9310-6 deg-1, indicating an almost isotropic thermal expansion of zirconolite-3T. The lower CTE value compared to a pure synthetic zirconolite observed for zirconolite-3T might be attributed to the complex chemistry and polyphase nature of the material investigated.This investigation investigates geologically old, ca. 370 Ma, metamict zirconolite from the Kovdor phoscorites and carbonatites in the Kola Alkaline Province. Mineral composition, crystallisation behaviour, and thermal expansion of the recrystallised samples were analysed using electron microprobe analysis, Raman spectroscopy, and in situ high-temperature powder X-ray diffraction (HTPXRD). The zirconolite crystals investigated are different in their morphology, internal texture, composition, alteration degree, and can be divided into four distinct groups. The zirconolite is a high Nb and Fe3+ variety (10.8-24.1 wt.% Nb2O5 and 7.9-9.0 wt.% Fe2O3), it is enriched in Th (up to 8.7 wt.% ThO2), Ta (up to 5.3 wt.% Ta2O5) and rare earth elements (up to 5.0 wt.% REE2O3). Raman spectroscopy confirmed that metamict zirconolite is anhydrous. The recrystallisation process of the metamict zirconolite is complex, as detected by HTPXRD. A fluorite-type phase starts to crystallise at 420 degrees C. The formation of a pyrochlore phase can be identified at 750 degrees C. The major phases detected in the sample after the recrystallisation are: zirconolite-3T (53 wt.%), srilankite (25 wt.%), pyrochlore (15 wt.%), baddeleyite (5 wt.%) and zircon (3 wt.%). The average coefficients of thermal expansion (CTE) values in the temperature range 25-1200 degrees C are as follows: ${{\bar \alpha }}$a = ${{\bar \alpha }}$b = ${{\bar \alpha }}$11 = ${{\bar \alpha }}$22 = 8.9510-6 deg-1. Similarly, the thermal expansion along the c-axis yields a similar value: ${{\bar \alpha }}$a = ${{\bar \alpha }}$b = 8.9310-6 deg-1, indicating an almost isotropic thermal expansion of zirconolite-3T. The lower CTE value compared to a pure synthetic zirconolite observed for zirconolite-3T might be attributed to the complex chemistry and polyphase nature of the material investigated.

Two new cesium copper oxosulfates, Cs4Cu7O3(SO4)6 (1) and Cs4Cu7O3(SO4)6[Cu0.2O0.2] (2) which can be considered as representatives of the Cs4Cu7+xO3+x(SO4)6 series with x = 0 and x = 0.2, were prepared in evacuated silica tubes. Both compounds are triclinic, P1 and contain complex polynuclear ensembles of edge-sharing OCu4 tetrahedra decorated by sulfate anions; these building units are arranged into pseudo-layers. The partially disordered Cs+ cations fill the interstices in the structure. The overall topology of the two structures is very similar; however, in 2, the copper-oxide ensembles are additionally stitched by weakly occupied Cu–O fragments into pseudo-chains; this also results in essential disorder in the Cs sublattice. Both structures have very much in common with those of the puninite-euchlorine-fedotovite morphotropic series. We analyze the crystal chemical trends in this morphotropic series.