The effects of one-dimensional hydrogen on the ferroelastic transition and elasticity of stishovite are determined up to 52.5 GPa using x-ray diffraction, Raman spectroscopy, and first-principles calculations. In contrast to the well-studied hydrogen-free stishovite or that with hydrogarnetlike point defects, stishovite with hydrogen intercalation develops into the CaCl2-type phase at a remarkably low pressure of 3.3 GPa, but the shear instability is postponed to 17.3 GPa. We rationalize the decoupling of the ferroelastic transition by modeling the spontaneous strains using Landau theory, and reveal a two-stage hierarchical progression of lattice distortion. Strains are originated from SiO6 octahedra surrounding the channel-like hydrogen defects, then subsequently propagate to bulk lattice with increasing pressure. Despite being the lightest atom and x-ray invisible, the elastic properties of stishovite are highly sensitive to the hydrous defect. Hydrogen-bearing stishovite may therefore induce shear anomalies in hydrous slabs at much shallower mantle depths than previously thought.

The development of efficient and sustainable strategies for carbon capture and storage is essential to mitigate the escalating impacts of climate change. Mineral carbonation using calcium silicates offers a permanent and environmentally safe route for CO2 sequestration, but conventional approaches are limited by slow kinetics under ambient conditions and often rely on energy-intensive activation methods. Here, we report a novel solid-state approach to enhance the reactivity of natural wollastonite by employing Pulsed Laser Deposition (PLD) to fabricate thin films with tailored morphology. Unlike previous studies relying on synthetic targets, we directly used a natural wollastonite mineral for PLD. By varying the deposition atmosphere, we obtained compact films in vacuum and nanofoams in oxygen. While crystalline wollastonite is not preserved in the deposited films and amorphous calcium silicate phases are instead formed, both film morphologies exhibit significant CO2 uptake through carbonate formation. Comprehensive characterization was performed by a multitechnique approach, including variable-pressure scanning electron microscopy and scanning transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and contact angle measurements. The results revealed that nanofoam morphology promotes enhanced wettability, facilitates rapid CO2 uptake and retention, and ultimately leads to higher carbonation compared to compact films. This additive-free PLD approach provides a potentially scalable, low-energy platform for mineral-based CO2 capture, advancing the use of natural calcium silicates in carbon removal technologies.

The interplay between electronic correlations, density wave orders, and magnetism gives rise to several fascinating phenomena. In recent years, kagome metals have emerged as an excellent platform for investigating these unique properties, which stem from their itinerant carriers arranged in a kagome lattice. Here, we show that electronic structure of the prototypical kagome metal, Fe_3Sn_2, can be tailored by manipulating the breathing distortion of its kagome lattice with external pressure. The breathing distortion is suppressed around 15 GPa and reversed at higher pressures. These changes lead to a series of Lifshitz transitions that we detect using broadband and transient optical spectroscopy. Remarkably, the strength of the electronic correlations and the tendency to carrier localization are enhanced as the kagome network becomes more regular, suggesting that breathing distortion can be a unique control parameter for the microscopic regime of the kagome metals and their electron dynamics.

The high-pressure behaviour of hydroboracite [ideally CaMg[B3O4(OH)(3)](2)center dot 3H(2)O, Sp. Gr. P2/c with a similar to 11.769, b similar to 6.684, c similar to 8.235 angstrom, and beta similar to 102.6 degrees at room conditions] has been studied by two in-situ single-crystal synchrotron X-ray diffraction experiments up to about 15 GPa, using He as pressure-transmitting medium. Between 14.51(5) and 14.72(5) GPa, hydroboracite undergoes a first-order phase transition to its high-pressure polymorph, hydroboracite-II (likely monoclinic with a similar to 11.29, b similar to 6.297, c similar to 7.48 angstrom, and beta similar to 106 degrees, space group unknown). The isothermal bulk modulus (K-V0 = beta(-1)(P0,T0), where beta(P0,T0) is the volume compressibility coefficient) of hydroboracite was found to be K-V0 = 41.4(6) GPa. The destructive nature of the phase transition prevented any structure resolution of hydroboracite-II or even the continuation of the experiments at pressures higher than 15.45(5) GPa. In the pressure range 0-14.45(5) GPa, the compressional anisotropy of hydroboracite, indicated by the ratio between the principal components of the unit-strain ellipsoid, is epsilon(1):epsilon(2):epsilon(3) = 2.2:1.3:1. The P-induced deformation mechanisms at the atomic scale in hydroboracite are here described.

The high-pressure behaviour of hydroboracite [ideally CaMg[B₃O₄(OH)₃]₂·3H₂O, Sp. Gr. P2/c with a 11.769, b 6.684, c 8.235 Å, and β 102.6° at room conditions] has been studied by two in-situ single-crystal synchrotron X-ray diffraction experiments up to about 15 GPa, using He as pressure-transmitting medium. Between 14.51(5) and 14.72(5) GPa, hydroboracite undergoes a first-order phase transition to its high-pressure polymorph, hydroboracite-II (likely monoclinic with a 11.29, b 6.297, c 7.48 Å, and β 106°, space group unknown). The isothermal bulk modulus (KV0 = β−1P0,T0, where βP0,T0 is the volume compressibility coefficient) of hydroboracite was found to be KV0 = 41.4(6) GPa. The destructive nature of the phase transition prevented any structure resolution of hydroboracite-II or even the continuation of the experiments at pressures higher than 15.45(5) GPa. In the pressure range 0–14.45(5) GPa, the compressional anisotropy of hydroboracite, indicated by the ratio between the principal components of the unit-strain ellipsoid, is ε1:ε2:ε3 = 2.2:1.3:1. The P-induced deformation mechanisms at the atomic scale in hydroboracite are here described.

Dalyite, ideally K2ZrSi6O15, space group P1, is a rare potassium zirconium silicate in agpaitic alkaline rocks, i.e., rocks with (Na + K)/Al >= 1.2 in which complex zirconosilicate minerals can form. The structural evolution and compressibility of dalyite have been studied by in situ single-crystal synchrotron X-ray diffraction up to 20.52(5) GPa. In the pressure (P) range investigated, we observed: (1) a second-order (distortive) phase transition, from dalyite to dalyite-II (P1), between 9.90(5) and 10.68(5) GPa, and (2) a first-order phase transition, from dalyite-II to dalyite-III (P1), between 11.06(5) and 12.03(5) GPa. Fitting the P-unit-cell volume (V) data with a second-order Birch-Murnaghan equation of state (EoS) yielded a value of KV0 = 51.4(4) GPa for dalyite [V0 = 332.5(2) & Aring;3] and KV0 = 39(1) GPa for dalyite-III [V0 = 670(4) & Aring;3]; due to the narrow stability field of dalyite-II (similar to 1.3 GPa), its elastic parameters could not be determined. The structure accommodates the deformation induced by pressure by increasing anisotropy, from dalyite having a strain ellipsoid axial value of epsilon 1:epsilon 2:epsilon 3 similar to 1.69:1.28:1 [calculated between 0.22(5) and 9.90(5) GPa] to dalyite-III with epsilon 1:epsilon 2:epsilon 3 similar to 6.4:2.0:1 [calculated between 12.03(5) and 20.52(5) GPa]. Both phase transitions have been found to be fully reversible, and the high-pressure polymorph structures have been solved. From dalyite to dalyite-II and dalyite-III, the unit-cell is doubled, and the coordination of K polyhedra increases from eight- to ninefold. Interestingly, before the first phase transition, the SiO4 tetrahedra have a significant role in accommodating the bulk compression and show different bulk moduli [47(4), 74(14), and 108(20) GPa], but after the transition the compressibility is accommodated mainly by deforming the ZrO6 octahedra, the beta-wollastonite chains and the 4- and 6-membered tetrahedra rings. The deformation of the SiO4 tetrahedra and Zr polyhedra constitutes an unusual behavior, rarely observed in previous high-pressure studies.

We report two new high-pressure polymorphs of sodium carbonate, ε and ε-II, stable over ∼2 GPa and 11 GPa, respectively. The ε polymorph exhibits a doubling of the c unit-cell parameter relative to the γ and β phases, crystallizes in space group Cc, and has a bulk modulus of 47.6 (8) GPa, comparable to that of the γ phase. Its stability is confirmed using in situ single-crystal and large-volume press (LVP) experiments. Phase transitions observed over a broad pressure-temperature range allow us to refine the topology of the Na2CO3 phase diagram. By integrating precise single-crystal constraints with LVP observations, we propose an updated phase diagram that shows an expanded stability field for the incommensurate γ phase, and reveals a wide stability field for the ε phase at conditions relevant for the Earth's mantle. These results provide improved experimental constraints for the high-pressure behavior of sodium carbonate.

We report a comparative high-pressure crystallographic study of the RS- and S-forms of 9-fluoro-3-methyl-10-(4-methylpiperazin-1-yl)-7-oxo-2,3-dihydro-7H-[1,4]oxazino[2,3,4-ij]quinoline-6-carboxylic acid, encompassing ofloxacin (O), gamma-levofloxacin (L gamma), and levofloxacin hemihydrate (LH). Single-crystal and X-ray powder diffraction experiments reveal all three compounds are relatively soft and compressible due to dominant dispersive intermolecular interactions via parallel molecular packing of the main bodies. Each form undergoes distinct pressure-induced phase transitions, with L gamma exhibiting a low transition pressure at 1.14 GPa, while LH displays a unique sensitivity to the water content of the pressure-transmitting medium. Under inert conditions, LH remains stable up to similar to 5.1 GPa before a transition to a lower-symmetry polymorph but using certain media it can undergo a phase transition to a new unidentified phase. O shows subtle structural changes above 4.65 GPa in methanol-ethanol medium, though no definitive phase transition was observed in the single-crystal form. These findings provide critical insights into the pressure-dependent behaviour of fluoroquinolone antibiotics, with implications for solid form selection, formulation design, and mechanical stability during pharmaceutical processing.

Acid-activated phosphate-based geopolymers emerged as alternatives to Portland cement thanks to their promising mechanical and thermal properties, as well as their potential for the solidification/stabilisation of hazardous wastes. In this regard, a peculiar application field can be found in radioactive waste management operations, where the immobilisation of radionuclides is one of the primary objectives. However, limited knowledge is available regarding the effectiveness of this kind of binders in this context. This study investigated the use of a natural, chabazite-rich, volcanic tuff as a novel precursor for phosphate-based geopolymers in radioactive waste management applications. The effects of the phosphoric acid concentration and the curing temperature on the geopolymerisation process were assessed. Elemental dissolution tests were used to estimate the release of aluminium, silicon, and iron from the volcanic tuff, showing extensive aluminium release due to the instability of chabazite in acid environments. The mineralogical and microstructural evolution of the samples was examined via quantitative phase analysis by X-ray diffraction and scanning electron microscopy, confirming chabazite dissolution and the subsequent formation of crystalline taranakite phase primarily governed by phosphoric acid concentration. Caesium retention, a key requirement for radioactive waste conditioning, was assessed through leaching tests. All samples demonstrated excellent caesium immobilisation capabilities, outperforming traditional cementitious matrices and comparable to alkali-activated geopolymers. The samples also met the Italian waste acceptance criterion for radioactive waste disposal. Therefore, chabazite-rich volcanic tuff can serve as a viable, natural precursor for phosphate-based geopolymers, providing a lower-impact alternative to other commonly used precursors.

The first zeolites discovered were natural zeolites, more than 250 years ago. The current estimated world mine production of natural zeolites ranges between 3–4 Mt per year. This chapter provides an overview about the complex world of natural zeolites, with a journey through their crystal-chemistry, occurrence in Nature, principal properties (i.e., cation exchange capacity and molecular sieve ability, behaviour at non-ambient conditions), and their principal applications (i.e., in water and wastewater treatment, agronomy and environmental soil remediation, building industry).

The structural evolution and compressibility of ordered and disordered ankerite were investigated at pressures up to similar to 25 GPa using synchrotron single-crystal X-ray diffraction in a diamond-anvil cell. Ordered ankerite (space group R3) undergoes a discontinuous phase transition between 12.15 and 13.45 GPa to a high-pressure structure called ankerite-II (space group P1) that has Ca in an eightfold coordination. Disordered ankerite (R3c space group) does not undergo a phase transition in the investigated pressure range.A Birch-Murnaghan equation of state was used to fit the volume compressibility. Ordered ankerite [K0V = 95(1) GPa, K ' = 3.8(3)] appears slightly more compressible than disordered ankerite [K0V = 99(1) GPa, K ' = 2.7(1)]. The phase transition in ordered ankerite has a change in volume of similar to 0.6% and K13.45V = 110(11) GPa, K ' = 7(3) for ankerite-II. The possible significance of this different behavior of ordered and disordered ankerite is discussed.

Carbonate minerals are important in Earth's system sciences and have been found on Mars and in meteorites and asteroids, highlighting the importance of impacts in planetary processes. While extensively studied under static compression, the behavior of carbonates under shock compression remains underexplored, with no in situ X-ray investigations reported so far. Here we investigate natural magnesiosiderite (Fe_0.6Mg_0.4CO_3) under nanosecond laser-driven shock compression at pressures up to 150 GPa, coupled with in situ ultrafast synchrotron X-ray absorption spectroscopy (XAS). The interpretation of the experimental spectra is complemented using first-principles absorption cross-section calculations performed on crystalline phases at different pressures and on a dense liquid phase obtained using density functional theory-based molecular dynamics (DFT-MD) simulations. Under laser-driven shock compression, the magnesiosiderite crystal phase remains unchanged up to the melt. Under shock reverberation, the absorption spectra show changes similar to those attributed to a high-spin to low-spin transition observed under static compression. At higher pressures, the laser shock induces the formation of CO_4 tetrahedral units in the melt. Upon unloading from the shocked state, only a few nanoseconds later, the original magnesiosiderite phase is recovered.

The crystal structure and the pressure-mediated crystal-fluid interaction of mesolite have been re-investigated by a multi-methodological approach, based on single-crystal neutron diffraction and by in-situ single-crystal synchrotron X-ray diffraction, using a diamond anvil cell. The structure refinement based on neutron intensity data collected at 20 K confirms the general model previously reported for mesolite, but largely improves the description of the hydrogen-bond network (with accurate sites location, their libration regime and interactions). Twelve out of the nineteen oxygen sites in the crystal structure of mesolite are involved in H-bonds as donors or as acceptors, reflecting the complex configuration of the H-bonding network. In the high-pressure investigations, four different pressure-transmitting fluids have been employed: the non-penetrating Daphne oil 7575 and the potentially penetrating methanol:ethanol:H2O (1:1:1) mixture, distilled H2O and liquid Ne. The Daphne oil 7575 experiment provided insight into the intrinsic compressional behaviour of mesolite, without any pressure-induced crystal-fluid interaction, yielding an isothermal bulk modulus KV0 = 55.9(7) GPa (beta V0 = 0.0179(2) GPa-1). In the aqueous mixtures, H2O molecules have been observed to continuously penetrate into the structural cavities, firstly in the natrolite-and then in the scolecite-type sheets, in the pressure range 0.8-1.9 GPa. By comparing the results of this study to the literature data, there is an apparent correlation between the pressure at which the adsorption process occurs and the H2O concentration of the pressure-transmitting medium: a higher H2O fraction allows the over-hydration of the scolecite-type sheets at lower pressures. When compressed in liquid Ne, atoms of neon appear to be able to penetrate into the natrolite-type sheets, interacting with the extra-framework population via weak van der Waals forces.

The aim of this study is to verify the chemical reactivity between calcium hydroxide Ca(OH)(2) and 26 volcanic rocks from different quarry wastes and outcrops of Sardinia to assess their potential use as pozzolans in mortar production and their sustainable recovery in construction materials field. The rocks were analysed from a chemical-mineralogical-petrographic point of view using transmitted light optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), multiple thermal (TGA-DTA) analyses. In addition, petrophysical (porosity, real and bulk densities, water absorption, etc.) and mechanical tests (compressive, flexural and Point Load strengths) were determined on the experimental mortars made up with the more reactive selected pozzolans. The volcanic rocks are characterised by a highly variable content of glass (from 5% to 99 vol%) that strongly influences the chemical reactivity with lime, and by the presence of zeolites that may affect the lime-reaction. The results show that the pozzolans here studied exhibit highly variable reactivity with hydrated lime, as function on their compositional and microstructural features. The reactivity of pozzolans is primarily influenced by (i) weight fraction (variable between 5 % and 99 vol%), microstructure and hydration degree of the amorphous matrix, (ii) microporosity and specific surface area; and (iii) chemical-mineralogical alteration of the rock. The most reactive samples have a glassy microstructure with characteristic concentrically trending micro-cracks, or a diffuse microporosity made up by interconnected pores (mainly <10 microns in size). Samples with intermediate or poor reactivity contain moderate to low fractions of glass or exhibit significant mineralogical variability. Rock alteration negatively affects reactivity by forming secondary phases, which reduce the glass-to-mineral ratio. Furthermore, the presence of zeolites, clay-minerals, dolomite and calcite in both pyroclastites and perlitic facies, negatively affects the reactivity. Among the perlites samples, those with a devitrified matrix and secondary minerals (e.g., Ca-erionite) show particularly low reactivity. This study confirms that several volcanic lithologies in Sardinia can be exploited as raw materials for the production of pozzolanic mortars, thanks to their low production cost. In the cement industry, highly reactive pozzolans can (i) bond with portlandite produced during Portland cement hydration (ii) reduce clinker production, thereby lowering gas emissions, and (iii) decrease binder production costs by partially using low-cost raw materials from quarries or industrial waste.

AbstractThe high-pressure behaviour of inderborite [ideally CaMg[B3O3(OH)5]2(H2O)4⋅2H2O, space group C2/c with a≈ 12.14, b≈ 7.43, c≈ 19.23 Å and β ≈ 90.3° at room conditions] has been studied by two in situ single-crystal synchrotron X-ray diffraction experiments up to ~10 GPa, using He as pressure-transmitting fluid. Between 8.11(5) and 8.80(5) GPa, inderborite undergoes a first-order phase transition to its high-pressure polymorph, inderborite-II (with a≈ 11.37, b≈ 6.96, c≈ 17.67 Å, β ≈ 96.8° and ΔV ≈ 7.0%, space group unknown). The isothermal bulk modulus (KV0 = β−1P0,T0, where βP0,T0 is the volume compressibility coefficient) of inderborite was found to be KV0 = 41(1) GPa. The destructive nature of the phase transition prevented any structure resolution of inderborite-II or even the continuation of the experiments at pressures higher than 10.10(5) GPa. In the pressure range 0–8.11(5) GPa, the compressional anisotropy of inderborite, indicated by the ratio between the principal components of the Eulerian finite unit-strain ellipsoid, is ɛ1:ɛ2:ɛ3 = 1.4:1.05:1. The deformation mechanisms at the atomic scale in inderborite are here described. Our findings support the hypothesis of a quasi-linear correlation between the total H2O content and P-stability range in hydrated borates, as the pressure at which inderborite undergoes the phase transition falls in line with most of the hydrate borates studied at high-pressure so far.

A natural intermediate member of the scapolite solid solution {Me-47; chemical formula: (Na1.86Ca1.86K0.23Fe0.01)(Al(4.3)6Si(7.64))O-24[Cl-0.48(CO3)(0.48)(SO4)(0.01)]}, with the unusual I4/m space group, has been studied at various temperatures and combined high-T and high-P by means of in situ single-crystal and powder X-ray diffraction, using both conventional and synchrotron X-ray sources. In addition, single-crystal neutron diffraction data were collected at ambient-T and 685 degrees C. A fit of the experimental V-T data with a thermal equation of state yielded a thermal expansion coeficient at ambient conditions: alpha(V25 degrees C) = 1/V-0 center dot(partial derivative V/partial derivative T)(P,25 degrees C) = 1.74(3)center dot 10(-5) K-1. A comparative analysis of the elastic behavior of scapolite based on this study and previous high-T XRD data suggests that a thorough re-investigation of the diferent members of the marialite-meionite solid solution is needed to fully understand the role of crystal chemistry on the thermal behavior of these complex nonbinary solid solutions. The experimental data obtained within the full temperature range of analysis at ambient pressure confirm that the investigated sample always preserves the I4/m space group, and possible implications on the metastability of I4/m intermediate scapolite are discussed. Neutron difraction data show that no significant Si and Al rearrangement among the T sites occurs between 25 and 685 degrees C. The combined high-T and high-P data show that at 650 degrees C and between 10.30(5) and 10.71(5) GPa a phase transition toward a triclinic polymorph occurs, with a positive Clapeyron slope (i.e., dP/dT > 0). A comprehensive description of the atomic-scale structure deformation mechanisms induced by temperature and/or pressure, including those leading to structural instability, is provided based on single-crystal structure refinements.

The encapsulation of Radioactive Reactive Metallic Waste (RRMW) in ordinary Portland cement poses significant challenges due to its incompatibility with the alkaline environment of the matrix. To address this issue, magnesium phosphate cements (MPC) emerge as potential solutions for the safe and effective immobilisation of RRMWs. The radiation stability and durability of an optimised formulation have been examined for samples irradiated up to 1000 kGy, in particular concerning the leaching behaviour of the three main constituents of the cement hydration products, and on four artificially added elements used to simulate radionuclides commonly found in radioactive waste (caesium, strontium, europium, and cobalt). The mortars exhibited excellent leaching behaviour and a high mechanical resistance, even after irradiation, freeze-thaw cycles, and water immersion. No significant radiation-induced effects were observed in the mineralogical and microstructural properties of the mortars, thus supporting their stability at the examined doses. Having verified the compliance with the main Italian waste acceptance criteria, the results of this research represent an encouraging step for the future implementation of MPCs for RRMWs conditioning.

Structural variations of natural clinochlore with pressure have been studied by in situ single-crystal X-ray diffraction (XRD) in a diamond-anvil cell in the pressure range 0-20 GPa at room temperature. High-resolution XRD data allowed for the identification of a polytypic phase transition at about 9 GPa. Around 4.32(5) GPa, the unit-cell parameters exhibited a significant deviation from linear behavior, particularly the c and beta values, abruptly interrupted when the phase transition occurs. XRD patterns showed a drastic reduction of diffuse scattering due to the stabilization of the high-pressure structure, suggesting that the atomic reorganization of the layers led to a disorder reduction. The phase transition showed complete reversibility during the experiment. Ab initio structural refinements identified the transition as polytypic, from the initial IIb-4 triclinic polytype (space group C1) to the IIa-1 monoclinic structure (space group C2/m), with unit-cell parameters a = 5.2058(6) & Aring;, b = 9.0208(4) & Aring;, c = 13.560(7) & Aring;, beta = 97.34(3)degrees. The latter was theoretically derived in the 1960s as the least stable chlorite polytype but has never been observed in natural chlorites. The phase transition also has a significative effect on the bulk modulus, with a reduction from K0 = 81.2(13)t to K0 = 56.0(6) GPa for the high-pressure structure. An isothermal run at 600 K from ambient pressure to 14 GPa showed the same phase transition at 7.8(5) GPa. Its occurrence at lower pressures suggests a negative P/T slope for the transition. Therefore, at high-temperature and high-pressure conditions compatible with impact phenomena, the polytypic phase transition could prevent chlorite from early destabilization and dehydration.

The crystal chemistry of inderite, a hydrous borate with known ideal formula MgB3O3(OH)5·5H2O from the Kramer deposit, was re-investigated by electron probe micro-analysis in wavelength dispersive mode, laser ablation-(multi collector-)inductively coupled plasma-mass spectrometry and single-crystal neutron diffraction. The chemical data prove that the real composition of the investigated inderite is substantially identical to the ideal one, with insignificant content of potential isomorphic substituents, so that, excluding B, inderite does not contain any other industrially-relevant element (e.g., Li concentration is lower than 2.5 wt ppm, Be or REE lower than 0.1 wt ppm). The average δ11BNIST951 value of ca. − 7 ‰ lies within the range of values in which the source of boron is ascribable to terrestrial reservoirs (e.g., hydrothermal brines), rather than to marine ones. Neutron structure refinements, at both 280 and 10 K, confirm that the building units of the structure of inderite consist of: two BO2(OH)2 tetrahedra (B-ion in sp3 electronic configuration) and one BO2(OH) triangle (B-ion in sp2 electronic configuration), linked by corner-sharing to form a (soroborate) B3O3(OH)5 ring, and a Mg-octahedron Mg(OH)2(OH2)4. The B3O3(OH)5 ring and the Mg-octahedron are connected, by corner-sharing, to form an isolated Mg(H2O)4B3O3(OH)5 (molecular) cluster. The tri-dimensional edifice of inderite is therefore built by heteropolyhedral Mg(H2O)4B3O3(OH)5 clusters mutually connected by H-bonds, mediated by the zeolitic (“interstitial”) H2O molecules lying between the clusters, so that the correct form of the chemical formula of inderite is Mg[B3O3(OH)5](H2O)4·H2O, rather than MgB3O3(OH)5·5H2O. All the thirteen independent oxygen sites of the structure are involved in H-bonding, as donors or as acceptors. This confirms the pervasive nature and the important role played by the H-bonding network on the structural stability of inderite. The differences between the crystal structure of the two dimorphs inderite and kurnakovite are discussed.

Abstract Fe1-x O, although chemically simple, possesses a complex structural and magnetic phase diagram. The crystal structures of Fe1-x O and its magnetic properties at extreme conditions are still a matter of debate. Here, we performed a systematic investigation on Fe0.94O up to 94 GPa and 1700 K using synchrotron X-ray diffraction and synchrotron Mössbauer source spectroscopy. We observe a transition of Fe0.94O to the monoclinic phases above 40 GPa and at high temperatures and use the group theory analysis of the observed phases to discuss their properties and their relation to the ambient pressure phases. The Mössbauer spectra of the rhombohedral and the room temperature monoclinic phase contain a component attributed to Fe2.5+, caused by the electron exchange between the Fe3+ defect and neighboring Fe2+ atoms. Our results present a structural and magnetic transitional pressure-temperature diagram of Fe1-x O and show the complex physicochemical properties of simple Fe1-x O binary oxide under extreme conditions.