Hydrothermal synthesis of [M(2-Et-Im)2] (M = Cd, Zn and 2-Et-Im = 2-ethylimidazolate) brings to the formation of low-quartz analogue phases, with space group P3121, typically as fine powders. In such metal-organic frameworks, tetrahedral M2+ coordination centres and bent anionic ligand bridges act as the tetrahedral Si4+ cations and O2- bridges in pure SiO2 quartz. In general, this class of compounds are thermally and chemically stable and a number of such phases (commonly known as Zeolitic Imidazolate Frameworks or ZIFs) have open porous structures with prospects for gas separation [1]. Differential Scanning Calorimetry (DSC) and X-ray powder diffraction at variable temperature (VT-XRPD) indicate that the two compounds used in this work undergo phase transitions at temperatures of around 300oC for Zn and 400oC for Cd. Since the structure of the related polymer [Fe(2-Me-Im)2] was found to be in the high quartz P6422 space group [2], our assumption was that the phase transitions might be from a low- to a high-quartz structure. Improved crystal growth of [M(2-Et-Im)2] was found using 3:1 acetonitrile:water mixtures at 110oC for several days, giving specimens of up to 0.5 mm in size with variable racemic twinning. Therefore an in situ high-temperature single-crystal diffraction (HT-SCXRD) study has been undertaken. Preliminary results indicate a continuous phase transition, with no change of space group and a small deviation in the thermal evolution of unit-cell parameters and volume. In this case the crystal is mounted using glue for HT. When instead the crystal is mounted in a quartz vial and kept still with the use of quartz wool to avoid mechanical stress on its surfaces, a different behaviour is noted, and a sudden change in the evolution of unit-cell parameters occurs at the transition. Work is in progress to characterize the phase transition under these conditions. New in situ HT-SCXRD measurements are in hand where the crystal is kept under vacuum.

The present study focuses on the assessment of the effects of different activation methods on carbonate-rich clays, to understand the mineralogical differences originated and to exploit such information to industry for traditional and innovative applications, especially as a precursor for alkali activated binders. Illite carbonate-rich clay samples were subjected to thermal activation in ox/red atmosphere between 400 and 900 °C, mechanical activation (grinding for 5, 10 and 15 min) and to a combination of such treatments. Mineralogical and textural changes in the activated samples were evaluated through X-ray powder diffraction, Fourier transform infrared spectroscopy and thermal techniques. The activated samples with the highest content of amorphous phase underwent leaching tests in a 3 M NaOH solution by means of inductively coupled plasma-mass spectrometry. The application of the three processing routines, yielded three types of activated clays with different leaching modes of Si, Al, K and Ca: (1) high energy grinding preferentially delaminates clay minerals and reduces the grain size of calcite. K leaching reaches the highest values; (2) thermal heating at 800 °C increases relatively the Si/Al solubility ratio, but the absolute concentrations of these elements are equal or lower than those obtained from ground clays. The relatively higher leaching of Ca is influenced by the formation of non-stoichiometric and poorly crystalline Ca-silicates and -aluminosilicates; (3) high energy grinding combined with heating treatment yields an extended amorphisation, mainly at the expense of clay minerals, with the highest leaching of Si and Al, and the lowest of Ca. New formed K-feldspars inhibit the concentration of K in alkaline solution.

Phosphates are among the most complex and variegated compounds in the entire mineral kingdom. Currently the total number of distinctive phosphate species is about 300 and most of them contains hydrogen as OH, H2O or in HPO4 2- group. Hydrogen bond has a central role in stabilizing the hydroxy-hydrated phosphate (HHPh) structures because it supplies the additional bond-valence (0.1 - 0.3 vu) contribution to the anions. Hence the (PO4) groups can link easily to all other interstitial cations (Huminicki & Hawthorne, 2002). For this reason, most HHPhs are characterized by the presence of complex tridimensional networks of O-H…O hydrogen bonds, which connect the polyhedral units making up a three dimensional framework. Consequently, the dimensionality of the structural unit is controlled primarily by the amount and role of hydrogen in the structure (Hawthorne, 1998). This could explain the observed correlation between the position in the paragenetic sequence of pegmatitic phosphates, and the amount of H2O in their formula (Fisher, 1958). FTIR spectroscopy is a powerful tool for the study of hydrogen in minerals, but HHPhs are rather challenging to study because of their complex structures. Moreover, due the high OH/H2O contents, these minerals show extremely intense IR absorptions in the OH region. In this work, we describe the results obtained by IR spectroscopy in different spectral regions of selected phosphates (veszelyite, whiteite, vauxite, paravauxite, metavauxite, augelite, wardite, wavellite, lazulite, arrojadite). O-H and hydrogen bonds orientation were studied by single crystal polarized light m-IR-spectroscopy, and experiments at HT- and LT were performed to study phase transitions and dehydration mechanisms with the aim of defining the thermal stability of these minerals. Finally, some applications done by using the novel FPA-FTIR imaging methods are presented. Fisher D.J. 1958. Pegmatite phosphates and their problems. Am. Mineral., 43, 181-207. Hawthorne F.C. 1998. Structure and chemistry of phosphate minerals. Mineral. Mag., 62, 141-164. Huminicki D.M.C. & Hawthorne F.C. 2002. The Crystal Chemistry of the Phosphate Minerals. In: Kohn M.L., Rakovan J. & Hughes J.M. Eds., Phosphates Geochemical, Geobiological, and Materials Importance. Rev. Mineral. Geochem., 48, 123-254.

The crystal structure of fibroferrite, Fe(OH)SO4•5H2O, was studied by means of single-crystal X-ray diffraction and vibrational (FTIR and Raman) spectroscopies. The new diffraction data allowed to successfully locate eleven H positions and to completely define the H bond system that ensures the cohesion of the Fe-O-S chains in the fibroferrite structure. Infrared and Raman spectra are presented for the first time for this compound and commented on the basis of the crystal structure and literature data for sulfate minerals. Both FTIR and Raman spectra show, in the fundamental water stretching region, a very broad absorption extending from 3600 to 2600 cm−1; peaks at 3522, 3411 and 3140 cm−1 can be resolved in the Raman pattern. The bands present in the lowwavenumber (<1300 cm−1) region are assigned on the basis of the literature data for similar substances, and the observed multiplicity is in agreement with a symmetry reduction of the sulfate ion in the structure of fibroferrite.

The aim of this work is to investigate the efficiency of the phyllomanganate birnessite in degrading catechol after mechanochemical treatments. A synthesized birnessite and the organic molecule were grounded together in a high energy mill and the xenobiotic-mineral surface reactions induced by the grinding treatment have been investigated by means of X-ray powder diffraction, X-ray fluorescence, thermal analysis and spectroscopic techniques as well as high-performance liquid chromatography and voltammetric techniques. If compared to the simple contact between the birnessite and the organic molecule, mechanochemical treatments have revealed to be highly efficient in degrading catechol molecules, in terms both of time and extent. Due to the two phenolic groups of catechol and the small steric hindrance of the molecule, the extent of the mechanochemically induced degradation of catechol onto birnessite surfaces is quite high. The degradation mechanism mainly occurs via a redox reaction. It implies the formation of a surface bidentate inner-sphere complex between the phenolic group of the organic molecules and the Mn(IV) from the birnessite structure. Structural changes occur on the MnO6 layers of birnessite as due to the mechanically induced surface reactions: reduction of Mn(IV), consequent formation of Mn(III) and new vacancies, and free Mn2+ ions production.

The existence of a lot of worldwide pentachlorophenol-contaminated sites has induced scientists to concentrate their effort in finding ways to degrade it. Therefore, an effective tool to decompose it from soil mixtures is needed. In this work the efficiency of the phyllomanganate birnessite (KBi) in degrading pentachlorophenol (PCP) through mechanochemical treatments was investigated. To this purpose, a synthesized birnessite and the pollutant were ground together in a high energy mill. The ground KBi-PCP mixtures and the liquid extracts were analyzed to demonstrate that mechanochemical treatments are more efficient in removing PCP than a simple contact between the synthesized birnessite and the pollutant, both in terms of time and extent. The mechanochemically induced PCP degradation mainly occurs through the formation of a surface monodentate inner-sphere complex between the phenolic group of the organic molecules and the structural Mn(IV). This is indicated by the changes induced in birnessite MnO6 layers as a consequence of the prolonged milling with the pollutant. This mechanism includes the Mn(IV) reduction, the consequent formation of Mn(III) and new vacancies, and free Mn2+ ions release. The PCP degradation extent is limited by the presence of chloro-substituents on the aromatic ring.

Iron oxides are transition metal oxides of paramount importance for their technological applications. Their synthesis can be performed by a variety of methods, most of which are chemical methods. Hematite, α-Fe2O3, can also be produced from iron sulfates by heating them sufficiently in air. In this work we have employed the thermal decomposition method to obtain hematite from the dehydration of fibroferrite, FeOH(SO4)·5H2O, a secondary iron-bearing hydrous sulfate. The study was performed via Rietveld refinement based on in-situ synchrotron X-ray powder diffraction combined with thermogravimetric analysis and mass spectrometry. The integration of the data from these techniques allowed to study the structural changes of the initial compound, determining the stability fields and reaction paths and its high temperature products. Six main dehydration/transformation steps from fibroferrite have been identified in the heating temperature range 30-798 °C. In the last step of the heating process, above 760 °C, hematite is the final phase. The temperature behavior of the different phases was analyzed and the heating-induced structural changes are discussed.

The crystal structure of hohmannite, Fe3+2 [O(SO4)2]·8H2O, was studied by means of single-crystal X-ray diffraction (XRD) and vibrational spectroscopy. The previous structural model was confirmed, though new diffraction data allowed the hydrogen-bond system to be described in greater and more accurate detail. Ab initio calculations were performed in order to determine accurate H positions and to support the experimental model obtained from XRD data. Infrared and Raman spectra are presented for the first time for this compound and comments are made on the basis of the crystal structure and the known literature for sulfate minerals.

A crystal-chemical investigation of vauxite, ideally FeAl2(PO4)2(OH)2 6H2O, from Llallagua (Bolivia) has been performed using a multi-methodological approach based on WDS-electron microprobe, single-crystal X-ray diffraction, and vibrational spectroscopies (Raman and FTIR). The structure was refined in the triclinic P1 space group, with the following unit-cell constants: a 9.1276(2), b 11.5836(3), c 6.15960(10) Å, a 98.3152(10)°, b 92.0139(10)°, g 108.1695(9)°, and V 610.05(2) Å3. The vauxite structure is based on a building unit oriented parallel to the c axis and composed of a chain of Fe2 and Al2 edge-sharing octahedra and two chains of corner-sharing P2 tetrahedra and Al1 octahedra, interconnected via corners and P1 tetrahedra. Neighboring building units are interconnected by Al3 octahedra and via Fe1 octahedra. The framework is completed with two non-coordinated water molecules. The latter, together with the two hydroxyl groups and the other four coordinated water molecules, form a complex hydrogen bonding network whose interactions further compact the whole framework. Both FTIR and Raman spectra show, in the H2O stretching region, a broad absorption consisting of several overlapping components due to the six water molecules plus the OH groups. The band multiplicity observed in the low-wavenumber region (o1400 cm–1) is compatible with the presence of two distorted PO4 tetrahedra.

The hydrated copper-aluminium sulphate cyanotrichite, ideally Cu4Al2(SO4)(OH)122H2O, often occurs in sky blue clumps or aggregates of sub-millimeter sized fibrous crystals. The problem of indistinguishable admixing of variable amounts of carbonate-cyanotrichite with cyanotrichite, the close association with other copper sulphates (chalcoalumite, brochantite) and the very small size of the acicular crystals hampered to date an ab initio structure determination from conventional X-ray diffraction. In light of these difficulties, we have taken advantage of the recent development of precessed automated electron diffraction tomography (ADT) combined with synchrotron powder X-ray diffraction to investigate the crystal structure of cyanotrichite. Through ADT investigation, two similar monoclinic cell were determined, corresponding to cyanotrichite (a = 10.16, b = 2.90, c = 12.64 Å and β = 92.4°) and carbonatecyanotrichite (a = 10.16, b = 2.91, c = 12.42Å and β = 98.4°). A structure model was obtained ab initio by direct methods in space group C2 from electron diffraction data and tested with the Rietveld method against X-ray powder diffraction profiles. All reflections in the powder pattern were indexed with the two cyanotrichite-like phases, according to electron diffraction data. The Rietveld analysis, consistently with electron diffraction investigations, indicates that the refined structural model has based on Al(OH)6 octahedra interconnected through common edges to build infinite columns running along b. Each Al-columns is coupled by sharing the remaining edges to two Cu-columns based on Cu distorted octahedra giving rise to ribbons along b. These ribbons are linked by SO4 tetrahedra to form corrugated layers.

A suite of Ti-bearing garnets from magmatic, metamorphic and carbonatitic rocks was studied by Electron Probe Microanalysis (EPMA), X-ray Powder Diffraction (XRPD), Single Crystal X-ray Diffraction (SCXRD), Mössbauer spectroscopy and Secondary Ion Mass Spectrometry (SIMS) in order to better characterize their crystal chemistry. The studied garnets show TiO2 varying in the ranges 4.9(1)-17.1(2) wt.% and variable Fe3+/ΣFe content. SIMS analyses allowed quantification of light elements yielding H2O in the range 0.091(7)-0.46(4), F in the range 0.004(1)-0.040(4) and Li2O in the range 0.0038(2)-0.014(2) wt%. Mössbauer analysis provided spectra with different complexity, which could be fitted to a number of components variable from one (YFe3+) to four (YFe2+, ZFe2+, YFe3+, ZFe3+). A good correlation was found between the Fe3+/ΣFe resulting from the Mössbauer analysis and that derived from the Flank method (Höfer & Brey, 2007). X-ray powder analysis revealed that the studied samples are a mixture of different garnet phases with very close cubic unit cell parameters as recently found by other authors (Antao, 2013). Single crystal X-ray refinements using anisotropic displacement parameters were performed in the Ia-3d space group and converged to R1 in the range 1.63-2.06 % and wR2 in the range 1.44-2.21 %. Unit cell parameters vary between 12.0641(1) and 12.1447(1) Å, reflecting different Ti contents and extent of substitutions at tetrahedral site. The main substitution mechanisms affecting the studied garnets are: YR4+ + ZR3+ ↔ ZSi + YR3+ (schorlomite substitution); YR2+ + ZR4+ ↔ 2YR3+ (morimotoite substitution); YFe3+↔ YR3+ (andradite substitution) with ZR4+ = Ti; YR4+ = Ti, Zr; YR3+ = Fe3+, Al3+, Cr3+; ZR3+ = Fe3+, Al3+ and YR2+ = Fe2+, Mg2+, Mn2+. The 2YTi4++ ZFe2+ ↔ 2YFe3+ + ZSi4+, the hydrogarnet substitution [(SiO4)4-↔ (O4H4)4-], the F– ↔ OH– and the YR4+ + XR+ ↔ YR3+ + XCa2+, with YR4+ = Ti, Zr; YR3+ = Fe3+, Al3+, Cr3+; XR+ = Na, Li also occur. The garnet crystal chemistry and implications in terms of nomenclature and classification (Grew et al., 2013) are discussed. Antao S.M. 2013. The mystery of birefringent garnet: is the symmetry lower than cubic?. Powder diffr., 28(4), 281-287. Grew E.S., Locock A.J., Mills S.J., Galuskina I.O., Galuskina E.V. & Hålenius U. 2013. Nomenclature of the Garnet Supergroup. Am. Mineral., 98, 785-811. Höfer H.E. & Brey G.P. 2007. The iron oxidation state of garnet by electron microprobe: Its determination with the flank method combined with major-element analysis. Am. Mineral., 92, 873-885.