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C a 2.90 M e 0.10 2 + ( P O 4 ) 2 (with Me = Mn, Ni, Cu) &beta, tricalcium phosphate (TCP) powders were synthesized by solid-state reaction at T = 1200 &deg, C and investigated by means of a combination of scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR) spectroscopy, and luminescence spectroscopy. SEM morphological analysis showed the run products to consist of sub spherical microcrystalline aggregates, while EDS semi-quantitative analysis confirmed the nominal Ca/Me composition. The unit cell and the space group were determined by X-ray powder diffraction data showing that all the compounds crystallize in the rhombohedral R3c whitlockite-type structure, with the following unit cell constants: a = b = 10.41014(19) &Aring, c = 37.2984(13) &Aring, and cell volume V = 3500.53(15) &Aring, 3 (Mn), a = b = 10.39447(10) &Aring, c = 37.2901(8) &Aring, V = 3489.22(9) &Aring, 3 (Ni), a = b = 10.40764(8) &Aring, c = 37.3158(6) &Aring, V = 3500.48(7) &Aring, 3 (Cu). The investigation was completed with the structural refinement by the Rietveld method. The FTIR spectra are similar to those of the end-member Ca &beta, tricalcium phosphate (TCP), in agreement with the structure determination, and show minor band shifts of the (PO4) modes with the increasing size of the replacing Me2+ cation. Luminescence spectra and decay curves revealed significant luminescence properties for Mn and Cu phases.

The crystal structure of fibroferrite, Fe(OH)SO 4 ·5H 2 O, 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 low-wavenumber ( −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 high-temperature behavior of synthetic potassic-ferro-richterite was addressed to obtain data relevant to understanding petrogenetic processes as well as to testing complementarity and mutual calibration of single-crystal X-ray diffraction (XRD) analysis plus structure refinement (SREF) with single-crystal FTIR spectroscopy. This experimental approach aims at: (1) better quantifying the onset of deprotonation, its development and the amount, if any, of relict OH at the end of the process; (2) verifying whether or not the process is homogeneous within the crystal; and (3) evaluating local changes in cation environments close to the OH dipole. In this first part of a series of two papers, we report on the crystal-chemical characterization of potassic-ferro-richterite and on a single-crystal XRD study at high T . Detailed analysis of the available data allowed us to obtain a full characterization of the bulk and crystal chemistry of the studied crystal, hence improving the unit formula suggested by Redhammer & Roth (2002). In operando H T measurements up to 1073 K showed quite anomalous behavior with respect to pargasite/kaersutites, specifically a much lower T for the onset of the deprotonation process (around 500 K), and strongly anomalous behavior of the β angle, which shows inverse slopes for protonated and deprotonated phases. “Oxo-potassic-ferro-richterite” is formed upon deprotonation and remains stable at least up to 1073 K under the conditions of this study. Structure refinements from data collected at different temperatures allowed us to detect changes in the crystal-structure geometry and in turn to decipher the way in which amphiboles with such a peculiar composition respond to increasing T and deprotonation. The thermal expansivity coefficients α (×10 −5 K −1 ) are: potassic-ferro-richterite: α a = 1.30(6), α b = 0.93(6), α c = 0.12(3), α β = −0.49(5), α asinβ = 1.34(8), α V = 2.59(2); “oxo-potassic-ferro-richterite”: α a = 1.71 (3), α b = 0.97(1), α c = 0.193(8), α β = 0.22(1), α asinβ = 1.59(4), α V = 2.74(2).

In this work, we address the intensity evolution of the CO2 FTIR bands of cordierite as a function of increasing T, by comparing data obtained from in situ versus quenching measurements. A natural well-characterized cordierite from Kragero (Arendal region, Norway) was studied up to 1200 °C using a heating stage fitted on a FTIR microscope. Two different oriented sections (001) and (010), respectively, were examined in order to check for the effect of the channel orientation on the CO2 release from the matrix. Spectra collected in situ show that increasing temperatures induces an increase in peak width for all CO2-related bands. The effects on the integrated absorbance A i are different for the different modes. Most notably, the integrated intensity A i of the anti-symmetric stretching mode (ν3) increases significantly up to 800 °C and then progressively decreases to 1000/1200 °C, depending on the sample orientation. Data obtained on quenched samples reveal that there is no variation in the band intensity for T

Lutetium beta-tricalcium phosphate Ca9Lu(PO4)(7) was synthesized by solid-state reaction at 1200 degrees C, and investigated by means of a combination of scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Raman spectroscopies. SEM morphological analysis reveals the presence of sub spherical and prismatic micro crystalline aggregates, while EDS semi-quantitative analysis confirms the nominal Lu/Ca composition. The unit cell and the space group were determined by X-ray powder diffraction data showing that the compound crystallizes in the rhombohedral R3c whitlockite-type structure, with unit cell constants a = b = 1.04164(1) nm, c = 3.7302(1) nm and cell volume V = 3.5051(1) nm(3). The investigation was completed with the structural refinement by the Rietveld method, and discussion of the distribution of Lu within cationic sites according to the results of the Rietveld refinement. The FTIR and Raman spectra, correlated to isostructural rare earth phosphates from literature, show slight band shifts of the phosphate modes correlated to the evolving size of the rare earth elements. (C) 2018 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights reserved.

The thermal dehydration of hohmannite, Fe2[O(SO4)2]·8H2O, a secondary iron-bearing hydrous sulfate, was investigated by in situ high-temperature X-ray powder diffraction and in situ high-temperature Fourier transform infrared spectroscopy. Combination of the data from both techniques allowed determining the stability fields and reaction paths for this mineral and its high temperature products. Five main dehydration/transformation steps for hohmannite have been identified in the heating range of 25–800 °C. Temperature behavior of the different phases was analyzed, and the heating-induced structural changes are discussed.

In order to clarify details of volatiles incorporation in arrojadites, two samples p\reviously characterized by X-ray diffraction and electron-microprobe (EMP) and LA-ICPMS analysis were investigated by single-crystal FTIR spectroscopy. The present study confirms and makes more quantitative previous results by single-crystal structure refinement about the presence and orientation of three OH − groups (one with partial occupancy) in the arrojadite structure. The FTIR spectra showed the presence of NH 4 + in arrojadite from Yukon, which was confirmed by EMP analysis ( ca . 700 ppm N). Micro FTIR imaging was used to check the homogeneity of OH and NH 4 + across the examined samples, as a prerequisite for the single-crystal polarized study. Based on the hydrogen bonding environment determined by structure refinement, the bands observed in the 3600–3500 cm −1 region can be assigned to the OH1 (at lower frequency) and OH2 (at higher frequency) dipoles. In the spectrum of arrojadite from Yukon several hyperfine components are resolved; these can be assigned to local Mg/ Fe 2+ octahedral configurations at the OH-coordinated octahedra. Both spectra show a very broad absorption extending from ~ 3500 to 2500 cm −1 which is assigned to the OH3 hydroxyl group. The orientation of the O-H dipoles calculated from the FTIR absorbance data are in excellent agreement with those calculated from the refined atomic coordinates, confirming the validity of the latter method also in the case of low-Z elements. Assuming the water content derived from EMP analysis, an integrated molar coefficient (polarized data) ɛ I = 63937 l/(mol□cm −2 ) is calculated for the spectroscopic quantification of H 2 O in arrojadite. For N, based on the EMP analysis, we obtain (for unpolarized data in the N-O bending region) ɛ i = 11000 ± 2000 l/(mol□cm −2 ) and ɛ I = 300 ± 60 l/(mol□cm −1 ) from integrated and linear intensity data, respectively.

We report a single-crystal Fourier-transform infrared (FTIR) study of a sample of pollucite from Maine, USA. Prior to our work, the sample had been characterized by single-crystal X-ray diffraction, neutron diffraction and electron-probe microanalysis. It is cubic Ia3d, with a crystal-chemical formula Na1.93(Cs10.48Rb0.31K0.04)Σ=10.83(Al14.45Si33.97)Σ=48.42O96·3.92H2O, and an H2O content, determined by thermogravimetric analysis, of 1.6 wt.%. The single-crystal FTIR spectrum has a doublet of intense bands at 3670 and 3589 cm–1, which are assigned to the ν3 and ν1 stretching modes of the H2O molecule, respectively. A very intense and sharp peak at 1620 cm–1 is assigned to the ν2 bending vibration. In the near-infrared region there is a relatively intense peak at 5270 cm–1, which is assigned to a combination (ν2 + ν3) mode of H2O, and a weak but well defined doublet at 7118 and 6831 cm–1, which is assigned to the first overtones of the fundamental stretching modes. A relatively weak but extremely sharp peak at 2348 cm–1 shows that the pollucite contains CO2 molecules in structural cavities. Mapping the sample using FTIR indicates that both H2O and CO2 are homogeneously distributed. Secondary ion mass spectrometry yielded an average CO2 content of 0.09±0.02 wt.%. On the basis of this value, we determined the integrated molar absorption coefficient for the spectroscopic analysis of CO2 in pollucite to be εiCO2 = 11,000±3000 l mol–1 cm–2; the linear molar absorption coefficient for the same integration range is εlCO2 = 1600±500 l mol–1 cm–1.

We report a FTIR (Fourier transform infrared) study of a set of cordierite samples from different occurrence and with different H2O/CO2 content. The specimens were fully characterized by a combination of techniques including optical microscopy, single-crystal X-ray diffraction, EMPA (electron microprobe analysis), SIMS (secondary ion mass spectrometry), and FTIR spectroscopy. All cordierites are orthorhombic Ccmm. According to the EMPA data, the Si/Al ratio is always close to 5:4; X Mg ranges from 76.31 to 96.63, and additional octahedral constituents occur in very small amounts. Extraframework K and Ca are negligible, while Na reaches the values up to 0.84 apfu. SIMS shows H2O up to 1.52 and CO2 up to 1.11 wt%. Optically transparent single crystals were oriented using the spindle stage and examined by FTIR micro-spectroscopy under polarized light. On the basis of the polarizing behaviour, the observed bands were assigned to water molecules in two different orientations and to CO2 molecules in the structural channels. The IR spectra also show the presence of small amounts of CO in the samples. Refined integrated molar absorption coefficients were calibrated for the quantitative microanalysis of both H2O and CO2 in cordierite based on single-crystal polarized-light FTIR spectroscopy. For H2O the integrated molar coefficients for type I and type II water molecules (ν3 modes) were calculated separately and are [I]e = 5,200 ± 700 l mol−1 cm−2 and [II]e = 13,000 ± 3,000 l mol−1 cm−2, respectively. For CO2 the integrated coefficient is $$ \varepsilon_{{{\text{CO}}_{ 2} }} $$ = 19,000 ± 2,000 l mol−1 cm−2.

This paper describes a single-crystal polarised-light FTIR study of the original emerald synthesised by HAUTEFEUILLE & PERREY (1888) using the flux method. The microchemical data show the analysed sample to be very close to the stoichiometric composition and homogeneous except for a significant variation in the Cr(2)O(3) content (from 1.45 to 2.59 wt%). Trace amounts of Ti. Mg. Fe. Zn. Na, K and F were also detected. The cell parameters are (in angstrom) a = 9.2264(25) and c = 9.1904(2), c/a = 0.9961. Despite the synthesis conditions, FTIR spectra in the OH-stretching region show the presence of weak but significant H(2)O vibrations in the crystals. The polarised FTIR spectra collected with E perpendicular to c consist of a unique sharp and intense band at 3643 cm(-1), whereas the E//c spectra consist of two minor bands at 3643 and 3587 cm(-1). These bands are assigned to the nu(3) antisymmetric stretching, and v, symmetric stretching modes of type 11 water in the structural channels, respectively. These water molecules are probably associated with Li impurities in the mineral, due to the flux employed for the syntheses. Using the molar absorption coefficient epsilon(i) = 27126 1 * mol(-1) * cm(-2) from the calibration curve of LIBOWITZKY & ROSSMAN (1997), a water content of similar to 30 ppm is derived for the studied emerald.

In this study, we describe the first FTIR measurements of CO2 desorption from cordierite, a microporous mineral stable up to high T conditions. To this purpose, we collected isothermal heating data on several (001) oriented sections of a well-characterized CO2-rich sample. Single-crystal slabs were heat-treated up to 1000 °C, and the intensity of the ν 3 antisymmetric stretching mode of CO2 at 2348 cm−1 was monitored as a function of time. The experimental data were modeled by using the mono-dimensional plane-sheet diffusion formalism; diffusion coefficients were plotted in the Arrhenius space and activation energies were calculated. Final data are as follows: −logD 0 = 4.2 ± 0.5 m2/s and E a = 208 ± 11 kJ/mol. Comparison with diffusion data from the literature (Lepezin and Osorgin in Rossijskaa Akademia Nauk 339:658–661, 1994) shows that at 800 °C H2O diffuses almost two orders of magnitude faster than CO2 along the structural channels of cordierite, with the difference in diffusion coefficients increasing at lower temperatures, and this implies that at lower temperatures H2O mobility is more favored compared to CO2. Therefore, the volatile contents measured in exhumed rocks may not reflect the H2O/CO2 ratio upon cordierite crystallization, and this could significantly affect the thermodynamic calculations for fluid activities or peak metamorphic conditions.

The thermal dehydration process of fibroferrite, FeOH(SO4)·5H2O, a secondary iron-bearing hydrous sulfate, was investigated by in situ high-temperature synchrotron X-ray powder diffraction (HT-XRPD), in situ high-temperature Fourier transform infrared spectroscopy (HT-FTIR) and thermal analysis (TGA-DTA) combined with evolved gas mass spectrometry. The data analysis allowed the determination of the stability fields and the reaction paths for this mineral as well as characterization of its high-temperature products. Five main endothermic peaks are observed in the DTA curve collected from room T up to 800 °C. Mass spectrometry of gases evolved during thermogravimetric analysis confirms that the first four mass loss steps are due to water emission, while the fifth is due to a dehydroxylation process; the final step is due to the decomposition of the remaining sulfate ion. The temperature behavior of the different phases occurring during the heating process was analyzed, and the induced structural changes are discussed. In particular, the crystal structure of a new phase, FeOH(SO4)·4H2O, appearing at about 80 °C due to release of one interstitial H2O molecule, was solved by ab initio real-space and reciprocal-space methods. This study contributes to further understanding of the dehydration mechanism and thermal stability of secondary sulfate minerals.

This paper reports a single-crystal unpolarized- light FTIR study in the OH-stretching region of a suite of well-characterized Ti-rich pargasites from Lherz (French Pyrenees). All amphiboles studied have fairly constant M-site composition, with Al-[6](tot) similar to 0.55 atoms per formula unit (apfia), Ti-[6] similar to 0.45 apfia, and Fe-[6](3+) similar to 0.40 apfu. SIMS and SREF data show all samples to have an 03 anion composition of OH approximate to O2- approximate to 1.0 apfu, with negligible F. The FTIR spectra show for all samples a broad absorption consisting of several overlapping bands; three main components can be recognized: similar to 3710, 3686, and 3660 cm(-1), respectively, with an asymmetric tail extending to lower frequency. Six Gaussian components can be fitted to the spectra; comparison with spectra of both synthetic and natural pargasites allows five of these components to be assigned to local configurations involving OH-O-2- at the 03 site, thus showing that coupling with an O2- anion through an A-cation significantly affects band position. Infrared spectroscopy can detect the presence of O2- in amphiboles in chemically favorable cases, i.e., in the absence of F. Moreover, the FTIR spectra show that all octahedral configurations involving Ti-M1(4+) or Fe-M1(3+) Fe-M3(3+) are associated with O2- at both adjacent 03 sites, and that Al-M3 is focally associated with OH, confirming SRO models based on structure refinement results.

We report here a single-crystal polarized-light study of stoppaniite, ideally (Fe,Al,Mg)4(Be6Si12O36)(H2O)2(Na,[]), from Capranica (Viterbo). Polarized-light FTIR spectra were collected on an oriented (hk0) section, doubly polished to 15 μm. The spectrum shows two main bands at 3,660 and 3,595 cm-1; the former is strongly polarized for E normal c, while the latter is polarized for E //c. A sharp and very intense band at 1,620 cm-1, plus minor features at 4,000 and 3,228 cm-1 are also polarized for E //c. On the basis of literature data and considering the pleochroic behavior of the absorptions, the 3,660 cm-1 band is assigned to the ν3 stretching mode and the 1,620 cm-1 (associated with an overtone 2*ν2 at 3,230 cm-1) band to the ν2 bending mode of “type II” water molecules within the structural channels of the studied beryl. The sharp band at 3,595 cm-1 is not associated with a corresponding ν2 bending mode; thus it is assigned to the stretching vibration of O–H groups in the sample. The minor 4,000 cm-1 feature can be assigned to the combination of the O–H bond parallel to c with a low-frequency metal-oxygen mode such as the Na–O stretching mode. The present results suggest that the interpretation of the FTIR spectrum of Na-rich beryl needs to be carefully reconsidered.

This paper relates the in situ X-ray diffraction and FTIR high- T study of pitiglianoite from Monte Cavalluccio (Campagnano, Rome, Italy), with composition Na 4.7 K 2.6 Ca 0.1 Si 6.1 Al 5.9 O 24 (SO 4 ) 0.8 · 2H 2 O. Upon heating, the cell parameters increased in the range 25–226 °C, following paths which were best fitted by the equations a = −1 × 10 −6 T 2 + 4 × 10 −4 T + 12.821 and c = −6 × 10 −7 T 2 + 2 × 10 −4 T + 5.264, for a and c , respectively. In the range 226–403 °C, there was a strong decrease of both a and c , while for T > 403 °C there was a new expansion of the structure. The FTIR data showed a major loss of both H 2 O and CO 2 in the range 200–400 °C. The structure of pitiglianoite at room- T , before the heating run, was characterised by columns of base-sharing undecahedral cages, containing chains of alternating Na cations and H 2 O molecules, and by large channels containing sulphate groups as well as Na and K ions. Structure refinement at 457 °C showed that all water was released from the cages and that significant extra-framework K (1.4 apfu) migrated from the large channel into the cages, throughout the hexagonal tetrahedral rings. A corresponding amount of Na cations migrated from the cages into the channels; a rotation of the sulphate groups, due to the presence of Na instead of K between two sulphate groups was also observed. Refinement at room- T after the experiment showed that the thermally-induced changes were substantially irreversible. The re-hydration of pitiglianoite was prevented by the Na ⇔ K cation exchange within the pores due to the thermal treatment.

Trioctahedral mica samples, collected at Cava St. Antonio (Mt. Vulture, Italy) were studied by combining electron-microprobe and C-H-N elemental analyses, single-crystal X-ray diffraction refinement, Mossbauer and Fourier transform infrared spectroscopies. Electron-microprobe analyses show the crystals to be quite homogeneous with TiO2 similar to 3 wt % and F ranging from 0.42 to 0.59 wt% Quantitative analyses of H combined with ferric/ferrous ratios from Mossbauer data allowed reliable crystal-chemical formulae to be derived. The results suggest that the entry of both Ti4+ and Fe3+ in the structure occurs through R-oxy substitution mechanisms involving deprotonation at O(4). This inference is supported by X-ray structure-refinement results (notably the c cell-parameter. the off-centering of the M2 cation towards O(4), the bond-length distortions of the cis-M2 octahedron) obtained using anisotropic thermal parameters in space group C2/m. The amount of oxy-substitutions from both electron-microprobe and X-ray data is in agreement with carbon-hydrogen-nitrogen analyses which give an average anion composition (OH1.25O0.65F0.10). Polarized-light infrared spectroscopy shows a complex OH-stretching spectrum which is composed of several overlapping (at least five) components. These can be assigned to the main octahedral local configurations that are compatible with the chemical composition. Pleochroic Fourier transform infrared spectroscopy measurements done along the principal optical directions show that the O-H bond axis is tilted from [001] and provide the average orientation of the O-H dipole in the structure: O-H (boolean AND) alpha similar to 23 degrees and O-H (boolean AND) gamma similar to 56 degrees.

In this work we investigate the strongly inhomogeneous distribution of CO2 and H2O in a synthetic beryl having a peculiar hourglass zoning of Cr due to the crystal growth. The sample was treated at 800°C, 500 MPa, in a CO2-rich atmosphere. High-resolution FESEM images revealed that the hourglass boundary is not correlated to physical discontinuities, at least at the scale of tens of nanometers. Polarized FPA-FTIR imaging, on the other side, revealed that the chemical zoning acts as a fast pathway for carbon dioxide diffusion, a feature never observed so far in minerals. The hourglass zone boundary may be thus considered as a structural defect possibly due to the mismatch induced by the different growth rates of each sector. High-resolution synchrotron-light FTIR imaging, in addition, also allows enhancement of CO2 diffusion along the hourglass boundary to be distinguished from diffusion along fractures in the grain. Therefore, FTIR imaging provides evidence that different diffusion mechanisms may locally combine, suggesting that the distribution of the target molecules needs to be carefully characterized in experimental studies. This piece of information is mandatory when the study is aimed at extracting diffusion coefficients from analytical profiles. Combination of TOF-SIMS and FPA data shows a significant depletion of type II H2O along the hourglass boundary, indicating that water diffusion could be controlled by the distribution of alkali cations within channels, coupled to a plug effect of CO2. © 2015 Della Ventura, Radica, Bellatreccia, Cavallo, Cinque, Tortora and Behrens.

This paper reports on water speciation and diffusion in synthetic beryl samples treated in CO2-rich atmosphere, at 700 MPa and 700 and 800 °C, respectively. The study has been conducted by means of polarized FTIR (Fourier transform infrared) integrated with FPA (focal plane array) imaging. As expected, the infrared spectra show the presence of CO2 but also of minor H2O interpreted as resulting from moisture present in the starting materials used for the experiments. FPA-FTIR images show that H2O diffuses into the beryl matrix along the structural channels oriented parallel to [001]. Spectra collected along profiles parallel to the c-axis show subtle changes as a function of the distance from the crystal edge; these changes can be correlated to a progressive change in the H2O coordination environment in the channel, as a response to the varying H2O/alkali ratio. In particular, the data show that when 2H2O > Na+ apfu (atoms per formula unit), H2O can assume both type I and type II orientation; in the latter case, each Na cation coordinates two H2O[II] molecules (doubly coordinated H2O). If 2H2O

The crystal chemistry of wavellite from Zbirov (Czech Republic), ideally Al3(PO4)2(OH,F)3·5H2O, was addressed by means of a multi-methodological approach based on electron microprobe analysis (EMPA) using wave-dispersive spectroscopy, single-crystal X-ray diffraction, powder and singlecrystal infrared spectroscopy and Raman spectroscopy. The EMPA data showed the presence of significant F replacing OH in the sample studied. The structure was solved in thePcmnorthorhombic space group, with the following unit-cell constants:a= 9.6422(7),b= 17.4146(15),c= 7.0094(2) Å,V= 1176.98(10) Å3. Phosphorus atoms display tetrahedral (PO4) coordination, while Al cations display octahedral coordination. The mineral framework can be viewed as the repetition of cationic arrays made up of AlO6polyhedra, bridged by PO4groups and further joined by O–H⋯O hydrogen bonds. The single-crystal unpolarized Fourier transform infrared (FTIR) spectrum shows combination bands indicating the presence of both OH and H2O in the structure. Both FTIR and Raman spectra show a broad absorption extending from 3600 to 2800 cm−1resulting from the overlapping of several components due to the water molecules and the OH group. The frequencies observed are comparable to those expected on the basis of the Libowitzky relationship for the range ofD–H⋯Abond systems in the structure.

This paper relates an infrared (IR) (6000–2500; 1400–400 cm–1) spectroscopic study of sideronatrite, Na2Fe3+(SO4)2(OH)·3H2O. Spectra in the 600–1250 cm–1 range are dominated by fundamental S–O absorption bands. Factor-group analysis based on the space group P212121(D42) is in accordance with the observed band multiplicity. A broad and convolute absorption centred around 3400 cm–1 and a sharp band at 3605 cm–1 are observed in the 2900–3900 cm–1 frequency region. The resolution of the broad band is significantly improved at liquid nitrogen temperature; seven components can be fitted to the pattern and these can be assigned to H2O/OH molecules in the structure. All components in the broad band and the sharp absorption at 3605 cm–1 are strongly polarized for E//a, in accordance with the structure analysis results. Infrared transmission spectroscopy is a useful tool to identify these sulfate minerals occurring in specific geological environments.

"The thermal stability of sideronatrite, ideally Na2Fe3+(SO4)(2)(OH)center dot 3(H2O), and its decomposition products were investigated by combining thermogravimetric and differential thermal analysis, in situ high-temperature X-ray powder diffraction (HT-XRPD) and Fourier transform infrared spectroscopy (HT-FTIR). The data show that for increasing temperature there are four main dehydration\/transformation steps in sideronatrite: (a) between 30 and 40 A degrees C sideronatrite transforms into metasideronatrite after the loss of two water molecules; both XRD and FTIR suggest that this transformation occurs via minor adjustments in the building block. (b) between 120 and 300 A degrees C metasideronatrite transforms into metasideronatrite II, a still poorly characterized phase with possible orthorhombic symmetry, consequently to the loss of an additional water molecule; X-ray diffraction data suggest that metasideronatrite disappears from the assemblage above 175 A degrees C. (c) between 315 and 415 A degrees C metasideronatrite II transforms into the anhydrous Na3Fe(SO4)(3) compound. This step occurs via the loss of hydroxyl groups that involves the breakdown of the [Fe3+(SO4)(2)(OH)] (a) (2-) chains and the formation of an intermediate transient amorphous phase precursor of Na3Fe(SO4)(3). (d) for T > 500 A degrees C, the Na3Fe(SO4)(3) compound is replaced by the Na-sulfate thenardite, Na2SO4, plus Fe-oxides, according to the Na3Fe3+(SO4)(3) -> 3\/2 Na-2(SO4) + 1\/2 Fe2O3 + SOx reaction products. The Na-Fe sulfate disappears around 540 A degrees C. For higher temperatures, the Na-sulfates decomposes and only hematite survives in the final product. The understanding of the thermal behavior of minerals such as sideronatrite and related sulfates is important both from an environmental point of view, due to the presence of these phases in evaporitic deposits, soils and sediments including extraterrestrial occurrences, and from the technological point of view, due to the use of these materials in many industrial applications"

The crystal chemistry of sekaninaite from Dolní Bory, Czech Republic, was characterized by a multimethod approach. Particular emphasis was put on the characterization of the channel constituents (i.e. H2O and CO2). Electron microprobe analysis shows the sample to be close to the Fe endmember [XFe = Fe/(Fe+Mg) = 94%) with significant Mn (1.48 wt.%) present; laser ablation mass-spectrometry showed the presence of 0.42 wt.% Li2O. H2O and CO2 contents (1.48 and 0.17 wt.%, respectively) were determined via secondary-ion mass-spectrometry. Sample homogeneity was checked by Fourier-transform infrared (FTIR) imaging using a microscope equipped with a focal plane array detector. Single-crystal FTIR spectroscopy confirmed the presence of two types of H2O groups in different orientations (with prevalence of the type II orientation), and that CO2 is oriented preferentially normal to the crystallographic c axis. Using the Beer-Lambert relation, integrated molar coefficients, εi, were calculated for both types of H2O (εi H2O[I] = 6000±2000; εi H2O[II] = 13000±1000) and for CO2 (εiCO2 = 2000±1000).

This paper reports an infrared spectroscopic study of a set of sodalite-group minerals. The specimens have been identified using a combination of X-ray diffraction and microchemical analysis. As expected, the Si/Al ratio is ∼1; the extra framework cation content is characterized by a well-defined Na ⇌ (Ca+K) substitution. The lattice parameters of the studied samples range from sodalite (sample LM11) with a = 8.889(2) A, to hauyne (sample HR3S) with a = 9.1265(2) A. The specimens, having the \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{SO}_{4}^{2-}\) \end{document} group as a dominant anion, show a clear correlation between the a cell edge and the K content. Single-crystal FTIR spectroscopy shows that hauyne and nosean typically contain enclathrated CO2 molecules, in addition to H2O and minor carbonate, while sodalite is virtually CO2-free. Detailed microspectrometric mappings show a non-homogeneous distribution of volatile constituents across the crystals, which may be related to the presence of fractures in the crystals. Because of such zoning, a relatively wide variation is observed when calibrating extinction coefficients on the basis of a bulk analytical method such as CHN elemental analysis.

We relate a single-crystal FTIR (Fourier transform infrared) and neutron diffraction study of two natural cancrinites. The structural refinements show that the oxygen site of the H(2)O molecule lies off the triad axis. The water molecule is almost symmetric and slightly tilted from the (0001) plane. It is involved in bifurcated hydrogen bridges, with Ow center dot center dot center dot O donor-acceptor distances >2.7 angstrom. The FTIR spectra show two main absorptions. The first at 3,602 cm(-1) is polarized for E perpendicular to c and is assigned to the nu(3) mode. The second, at 3,531 cm(-1), is also polarized for E perpendicular to c and is assigned to nu(1) mode. A weak component at 4,108 cm(-1) could possibly indicate the presence of additional OH groups in the structure of cancrinite. Several overlapping bands in the 1,300-1,500 cm(-1) range are strongly polarized for E perpendicular to c, and are assigned to the vibrations of the CO(3) group.

The P 2 1 / m ↔ C 2/ m phase-transition has been studied by high- T FTIR analysis on a series of synthetic amphiboles in the Li 2 O–Na 2 O–MgO–SiO 2 –H 2 O (LNMSH) system. Spectra were collected in the T range 25–450 °C on KBr disks. All examined amphiboles have P 2 1 / m symmetry at room T . Their OH-stretching FTIR spectrum consists of two main bands at ~3740 and 3715 cm −1 . At the transition temperature ( T c ), these bands merge into one single absorption centred at ~3720 cm −1 , and no further change is observed beyond this T . Significant modifications consisting in peak shifting and band broadening are also observed in the MIR (medium infrared) 1300–640 cm −1 region. T c values for the different compositions were estimated based on various methods; the most reliable procedure is considered to be the fit of Landau 2-4-6 potentials using band shifts observed in the MIR region. The T c values obtained for all samples are consistent with previous results obtained on two members of the series examined here by single-crystal or synchrotron powder H T -XRD (high- T X-ray diffraction). They correlate linearly with the aggregate cation radius at M (4) [ T c (°C) = 803–533 〈 r M (4) 〉; R 2 = 0.97]. This work thus provides a measure of the role played by the size of the M (4) polyhedron in determining the T c in simple chemical systems where the B-site occupancy (and geometry) is the only variable. The slope of the equation is far less steep in the LNMSH system than in cummingtonite; crystal-chemical reasons for this behaviour are discussed, and the local order between A and monovalent B cations is suggested to be the major constraint. In more complex systems, inspection of the available data shows that other factors such as the aggregate size of the strip of octahedra must be taken into account.

A multi-methodological study, based on electron microprobe analysis (in wavelength dispersive mode), single-crystal X-ray diffraction (XRD), transmission electron microscopy and single-crystal Fourier transform infrared spectroscopy was performed in order to describe the crystal chemistry of four leucite samples from different localities of the Roman Comagmatic Province (central Italy). All the crystals examined were found to be tetragonal (space group I41/a with a = 13.076–13.103 Å and c = 13.744–13.784 Å) and characterized by a complex twinning (merohedric twins: on the tetragonal planes (110) and (1̄10) with the two individuals having parallel crystallographic axes with a and b interchanged; pseudo-merohedric twins: on the tetragonal planes (101), (011), (1̄01), (01̄ 1), with the two individuals having parallel a (or b) axes and the remaining two axes not parallel). The chemical analyses show that all the samples contain minor Na and Fe. Infrared spectroscopy shows that all samples contain structurally bound water molecules, up to unexpectedly large amounts (~0.4 wt.%) for a nominally anhydrous mineral, suggesting that ‘analcime-like’ substitution (K to Na + H2O) occurs in the leucite samples investigated here. The detection limits of the ‘analcime-like’ substitution by singlecrystal XRD are also discussed.

Three natural amphibole samples collected from the former vermiculite mine near Libby, Montana. USA, have been analysed by Rietveld X-ray powder diffraction (XRPD) refinement and Fourier transform infrared spectroscopy (FTIR) in the OH-stretching region. The same materials have been analysed previously by electron microprobe analysis (EMPA), Mössbauer spectroscopy and structure refinement (SREF) single crystal X-ray diffraction (SC-XRD), which revealed that these amphiboles have a crystal chemical formula very close to an intermediate composition between winchite and richterite, i.e. AA0.5BNaCaCMg4.5M3+T0.5Si8O22(OH)2 (A = Na and/or K; M3+ = Fe3+ and/or Al). The Rietveld analysis showed the powder samples used for the experiments here to be composed only of amphibole. This in turn allowed us to use FTIR OH-stretching data to derive cation ordering on these powder samples. The three FTIR spectra are quite similar and up to four components can be fitted to the patterns. The two lower-frequency components (labelled A and B) can be attributed to a local O(3)-H dipole surrounded by M(1)M(3)Mg3 and M(1)M(3)Mg2Fe2+; (respectively), an empty A site and rSi8 environments; on the contrary, the higher-frequency C and D bands indicate the presence of an occupied A site. The FTIR OH-stretching data alone allow us to calculate the site occupancy of the A, M(1)–M(3) and T sites with confidence, as compared with previously published data. By contrast M(4)- and M(2)-site occupancies are more difficult to evaluate. This study takes advantage of the large database of well characterized synthetic amphiboles, built over the last two decades. The comparison of vibrational spectroscopy data with micro-chemical and crystallographic data reported in this study demonstrate that the FTIR OH-stretching method alone is a valuable and rapid method to derive or at least sensibly constrain site occupancy for natural amphiboles. A much more detailed cation site occupancy can be obtained by combining micro-chemical and FTIR OH-stretching data.

Synchrotron radiation FTIR polarized micro-spectroscopy has been used to investigate natural mica crystals in order to characterize the stretching vibrations of the OH groups and their orientation relative to the mica cleavage (0 0 1) plane. A procedure to eliminate undesired interference fringes, typically observed when working with thin single-crystals, was set up using an ad hoc sample preparation, and tested. The naturally high brilliance and high polarization properties of synchrotron radiation allows to study very small flakes and hence offers new analytical possibilities in comparison to conventional powder FTIR spectroscopy.

Synchrotron radiation FT-IR polarized micro-spectroscopy has been used to investigate the natural mica fluorophlogopite in order to characterize the stretching vibrations of the OH groups and their orientation relative to the mica cleavage (0 0 1) plane. A procedure to eliminate undesired interference fringes, typically observed when working with thin single-crystals, was set up using an ad hoc sample preparation, and tested. The naturally high brilliance and high polarization properties of synchrotron radiation allows to study very small flakes and hence offers new analytical possibilities in comparison to conventional powder FT-IR spectroscopy.

The synthetic amphibole Na0.95(Li0.95Mg1.05)Mg5Si8O22(OH)2 was studied in situ at high-T, using IR OH-stretching spectroscopy and synchrotron X-ray powder diffraction. At room-T the sample has P21 /m symmetry, as shown by the FTIR spectrum. It shows in the OH region two well-defined and intense absorptions at 3,748 and 3,712 cm−1, respectively, and two minor bands at 3,667 and 3,687 cm−1. The main bands are assigned to the two independent O–H groups in the primitive structure. The two minor bands evidencing the presence of small amount of vacant A-site (A□0.05). With increasing T, these bands shift continuously and merge into a unique absorption at high temperature. A change as a function of increasing T is revealed by the evolution of the refined unit-cell parameters, whose trend shows a transition to C2/m at about 320–330°C. The spontaneous scalar strain, fitted with a tricritical 2–6 Landau potential, gives a T c of 325(10)°C (β parameter = 0.27). Comparison with the second-order P21 /m ⇔ C2/m phase transition at 255°C for synthetic amphibole ANa 0.8 B (Na0.8Mg1.2)CMg5Si8O22(OH)2 indicates that the substitution of Na with Li at the B-sites strongly affects the thermodynamic character and the T c of the phase transition. The comparison of LNMSH amphiboles with cummingtonitic ones shows that the high-T thermodynamic behaviour is affected by A-site occupancy.

A well-characterized suite of vesuvianite samples from the volcanic ejecta (skarn or syenites) from Latium (Italy) was studied by single-crystal, polarized radiation, Fourier-transform infrared (FTIR) spectroscopy and secondary-ion mass-spectrometry (SIMS). OH-stretching FTIR spectra consist of a rather well-defined triplet of broad bands at higher-frequency (3,700-3,300 cm(-1)) and a very broad composite absorption below 3,300 cm(-1). Measurements with E//c or E perpendicular to c show that all bands are strongly polarized with maximum absorption for E//c. They are in agreement with previous band assignments (Groat et al. Can Mineral 33:609, 1995) to the two O(11)-H(1) and O(10)H(2) groups in the structure. Pleochroic measurements with changing direction of the E vector of the incident radiation show that the orientation of the 0(11)-H(l) dipole is OH(boolean AND)c similar to 35 degrees, in excellent agreement with the neutron data of Lager et al. (Can Mineral 37:763, 1999). A SIMS-based calibration curve at similar to 10% rel. accuracy has been worked out and used as reference for the quantitative analysis of H(2)O in vesuvianite by FTIR. Based on previous SIMS results for silicate minerals (Ottolini and Hawthorne in J Anal At Spectrom 16:1266, 2001; Ottolim et al. in Am Mineral 87:1477, 2002) the SiO(2) and FeO content of the matrix were assumed as the major factors to be considered at a first approximation in the selection of the standards for H. The lack of vesuvianite standards for quantitative SIMS analysis of H(2)O has been here overcome by selecting low-silica elbaite crystals (Ottolini et al. in Am Mineral 87:1477, 2002). The resulting integrated molar absorption FTIR coefficient for vesuvianite is epsilon(i) = 100.000 +/- 2.000 l mol(-1) cm(-2). SIMS data for Li, B, F, Sr, Y, Be, Ba REE, U and Th are also provided in the paper.