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Elucidating the high-temperature behavior of rock-forming minerals such as amphiboles (AB2C5T8O22W2) is critical for the understanding of large-scale geological processes in the lithosphere and, in particular, the development of high conductivity in the Earth’s interior. Recently, we have shown that at elevated temperatures, CFe-bearing amphiboles with a vacant Asite develop two types of charge carriers: (1) small polarons and (2) delocalized H+ions.

In this work we address the stability of riebeckite at high temperatures and compare the different behaviors observed under various oxidation conditions. For this purpose, we annealed powders of a sample from Mt. Malosa (Malawi), which is compositionally close to the end-member; the run products obtained after annealing in air vs. in vacuum were studied by Mössbauer spectroscopy and powder X‑ray difraction. The results show that riebeckite follows two distinct paths depending on the external environment. Under oxidizing conditions, it is stable in the hydrous form up to relatively low temperatures (400–450 °C), then it undergoes a rapid (within ~50 °C) dehydrogenation, forming oxo-riebeckite, which is stable up to ~900 °C. The final breakdown products of the oxo-amphibole include aegirine + cristobalite + hematite. Based on the relative intensity of the (310) Bragg reflection, the activation energy (Ea) for the riebeckite to oxo-riebeckite transition is 166 ± 6 kJ/mol.

In this work, we address the kinetics of dehydrogenation occurring at high temperatures (HT) in riebeckite, a sodic amphibole with the ideal composition Na2Fe23+Fe32+Si8O22(OH)2.${\rm{N}}{{\rm{a}}_2}{\rm{Fe}}_2^{3 + }{\rm{Fe}}_3^{2 + }{\rm{S}}{{\rm{i}}_8}{{\rm{O}}_{22}}{({\rm{OH}})_2}.$We performed isothermal experiments on both powders and single-crystals up to 560 °C and monitored the O-H stretching signal by Fourier transform infrared (FTIR) spectroscopy. Single-crystals show an initial increase in IR absorption intensity due to increasing vibrational amplitudes of the O-H bond stretching, not observed for powders. The OH-intensities vs. time were fitted using the formalism for first-order reactions. The calculated activation energies for H+diffusion in riebeckite are 159 ± 15 kJ/mol for powders and 216 ± 20 kJ/mol for single crystals, respectively. The exponential factor min the Avrami-Erofeev equation obtained for crystals ranges between 1.02 and 1.31, suggesting that, unlike powders, the dehydration process in crystals is not a purely first-order reaction. This implies that a second energy barrier must be considered, i.e., diffusion of H+through the crystal. FTIR imaging showed that H+diffusion occurs mainly perpendicular to the silicate double-chain. Our results confirm that the release of H+from riebeckite occurs after the irreversible Fe2+-to-Fe3+exchange, thus at temperatures >550 °C. To be effective, the process needs the presence of external oxygen that, by interacting with H+at the crystal surface, triggers the release of H2O molecules. This implies that oxidizing conditions are required for the amphibole to be an efficient water source at depth.

In this work the terahertz spectra of benzene, toluene, p-xylene and styrene–four volatile organic compounds (VOCs) of interest in environmental pollution studies–have been measured in their liquid phase at room temperature using terahertz time-domain spectroscopy (THz-TDS). Their frequency-dependent refractive index and absorption coefficient have been extracted and analyzed in the spectral range from 0.2 to 2.5 THz. The optical properties of bi-component VOCs mixtures have also been investigated and described in terms of a linear combination of pure VOCs optical components.

The low crystallinity of arsenic (As) containing minerals such as arseniosiderite and yukonite has made a detailed understanding of their atomic structures elusive. X-ray pair distribution function (PDF) and transmission electron microscopy (TEM) were used to gain a detailed understanding of the short and medium-range structural features. High-resolution synchrotron powder diffraction data showed long-range order in arseniosiderite occurs along one direction. PDF data confirmed arseniosiderite has the same general structure as robertsite and mitridatite but with the layers occasionally shifted to disrupt long-range order. Use of small box and reverse Monte Carlo modeling of the PDF data gave the first complete set of atomic coordinates for arseniosiderite. TEM confirmed the degree of interlayer order is generally high. PDF and TEM data show that yukonite is a nano-sized analog of arseniosiderite which lacks any long-range order but is locally similar. The structural evolution of arseniosiderite from yukonite was observed for the first time in a natural specimen viaTEM. PDF data on several yukonite samples reveal rather sudden drops in the degree of structural correlation as a function of distance. These drops occur from yukonite being composed of small layers made of integer numbers of large nonamers of edge-sharing FeO6octahedra, as seen in arseniosiderite. However, these layers are 2 or 3 nonamers in width, with little structural correlation between layers. Thus our work provides a more complete nano/microscopic picture of the key structural features in these minerals found in mining ores and wastes around the world.

Silver terbium diphosphate AgTbP2O7was prepared by solid state reaction at T=500° and characterized by combining SEM-EDS morphological investigation and semi-quantitative chemical analysis viaScanning Electron Microscopy (SEM) equipped with energy dispersive X-Ray spectroscopy (EDS), structure solution via Rietveld refinement of powder X-ray diffraction (PXRD) data, and Fourier transform infrared (FTIR) spectroscopy. The synthesized compound is monoclinic, P21/nspace group, with cell parameters: a=11.9108(3) Å, b=6.90265(16) Å, c=6.62030(15) Å, β=90.3702(5)° and V=544.28(2) Å3. The crystal structure consists of a network of zig-zag chains of TbO8polyhedra extending along the baxis, bridged by P2O7diphosphate groups and by chains of AgO7polyhedra running along the ccrystallographic direction. MIR (medium infrared) spectrum shows bands typical of P–O modes of diphosphate compounds. Observed band multiplicity is in agreement with the symmetry reduction with respect to orthorhombic rare earth diphosphates with similar stoichiometries reported in the literature.

•Water column samples showed higher microlitter levels than surface water.•Filaments were the most abundant microlitter shape in the water column.•Coastal sites showed a great abundance of microlitter than the offshore areas.•Coastal currents and land-based sources strongly influence microlitter distribution.•DELFT3D-FLOW and SWAN are effective in identifying microlitter enriched spots.

Lutetium β-tricalcium phosphate Ca9Lu(PO4)7was synthesized by solid-state reaction at 1200 °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 R3cwhitlockite-type structure, with unit cell constants a = b = 1.04164(1) nm, c = 3.7302(1) nm and cell volume V = 3.5051(1) nm3. 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.

The crystal structure of a new member of the calcium amphibole subgroup, vanadio-pargasite ideally NaCa2(Mg4V3+)Si6Al2O22(OH)2 with empirical formula (K0.07Na0.90)(Na0.05Ca1.91Mg0.04)S2.00(Mg4.02Cr0.05V0.68Al0.23Ti0.02)S5.00(Si6.09Al1.91)S8.00O22(OH1.67F0.33)S2.00, was studied by single-crystal X-ray diffraction and refined to R1 of 0.0181. It is monoclinic, space group C2/m, unit-cell parameters a?=?9.8956(1), b?=?17.9970(2), c?=?5.2970(1)?Å, ß?=?105.391(1)°, and V?=?909.52?Å3. The mineral is isostructural with the amphiboles pargasite, magnesio-hastingsite, chromio-pargasite and Mn3+-rich pargasite. Site populations were derived from the structure refinement and electron-microbe analysis, and validated on the basis of OH-stretching FTIR spectroscopy. Accordingly, V is ordered at M(2) together with minor [6]Al, while a low amount of [6]Al is present at M(3).

The HT behaviour of a well-characterized sample of riebeckite has been examined by combining X-ray diffraction, FTIR and Mössbauer spectroscopy. The crystal-chemical composition of the crystal studied is: A(K0.05Na0.04)  (Na1.86Ca0.09Fe0.052+) B (Fe2.942+Mg0.222+Mn0.022+Zn0.012+Fe1.743+Al0.063+Ti0.014+) C T(Si7.95Al0.05) O22 (OH1.9F0.10-) W . The onset of the deprotonation process is detected at ~700?K by single-crystal XRD analysis of the unit-cell parameters, but starts at 623?K as indicated by Mössbauer spectroscopy on powders (and by changes in the cation distribution observed by structure refinement). FTIR analysis shows that a completely deprotonated oxo-amphibole is obtained after annealing at 893?K. Room-T single-crystal structure refinements of the deprotonated phase shows a very peculiar cation disorder, which has never been observed in amphiboles until now: there is significant depletion of B and C cations coupled with an increase in A cations, which implies the presence of vacancies at the M(3) and the M(4) sites in double-chain silicates. FTIR data collected at 873?K confirm both this conclusion and the onset of the cation exchange before completion of deprotonation. Axial and volume thermal expansion coefficients were determined in the T range 298–698?K for riebeckite (aa?=?1.40(2)?·?10-5?K-1, ab?=?0.67(1)?·?10-5?K-1, ac?=?0.17(2)?·?10-5?K-1, aß?=?-0.07(1)?·?10-5?K-1and aV?=?2.27(2)?·?10-5?K-1) and in the 298–1173?K range for the oxo-amphibole (aa?=?1.53(2)?·?10-5?K-1, ab?=?0.77(1)?·?10-5?K-1, ac?=?0.25(1)?·?10-5?K-1, aß?=?0.10(1)?·?10-5?K-1and aV?=?2.52(2)?·?10-5?K-1).

The amphibole group of minerals comprises a large number of species, some of which have typically fibrous shapes and are thus of interest for environmental hazard issues. Their identification is complicated by the presence of light elements (H and Li), multi-valence elements (e.g. Fe, Mn) and a partially vacant structural site. Vibrational spectroscopies are valuable tools to address the quantitative determination of occupancies in amphiboles: however, whilst Fourier-Transform Infra-Red Spectroscopy (FTIR) has been preferentially used in crystal-chemical studies, Raman spectroscopy has been restricted to asbestos identification. In this work we focus our attention on two sets of well-characterised synthetic amphiboles, i.e. on samples along the potassium-richterite - tremolite join, and the Na(NaMg)Mg5Si8O22(OH)2 compound synthesised at different T and P conditions. We show that the Raman spectra in the OH-stretching region are very similar, in terms of band shape and multiplicity to the FTIR spectra; however, the relative intensity of the Raman peaks provides direct quantitative information on the A-site occupancy, a feature that has significant implications as a tool for asbestos studies.

In this work, we investigate the oxidation behavior of a nearly end-member riebeckite, ideally Na2(Fe32+Fe23+)$\begin{array}{} (\text{Fe}^{2+}_3\text{Fe}^{3+}_2) \end{array} $Si8O22(OH)2, by using vibrational FTIR and Raman spectroscopies. Combining these results with previous studies performed on the same sample by single-crystal structure refinement and Mössbauer spectroscopy, we conclude that iron oxidation in riebeckite is a multi-step process. (1) In the ~523 K < T< 623 K temperature range, the O-H bond lengthens and both the electrons and the hydrogen cations delocalize. Raman analysis shows that this step is reversible upon cooling to room temperature. (2) In the 623 K < T< 723 K range, the kinetic energy increases so that the electrons can be ejected from the crystal; beyond 723 K an irreversible oxidation of Fe occurs that couples with irreversible changes in the SiO4double-chains leading to a contraction of the unit-cell volume, i.e., to structural changes detectable at the long-range scale. (3) Beyond 823 K, the irreversible oxidation is completed and H+ions are forced to leave the crystal bulk. Because of this multi-step process, the onset of the deprotonation process is detected at ~700 K by single-crystal XRD analysis of the unit-cell parameters, but starts at 623 K as indicated by Mössbauer spectroscopy on powders (and by changes in the cation distribution observed by structure refinement). Also, Raman scattering shows that the release of H+from the crystal surface starts ~100 K before the complete deprotonation of the crystal bulk is witnessed by FTIR absorption. Hence, the oxidation of Fe starts at the crystal surface and induces electron and H+migration from the crystal interior to the rim and thus subsequent oxidation through the crystal bulk. No deprotonation is observed by FTIR either in powders embedded in KBr or in crystals heated in N2atmosphere, implying that the release of H+needs surficial (atmospheric) oxygen to form H2O molecules. Fe2+→ Fe3+oxidation produces a flux of electrons throughout the crystal matrix, which generates electrical conductivity across the amphibole. An important implication of this work, which might have interesting applications in material science, is that iron oxidation in riebeckite (and possibly in other Fe-rich silicates) is reversible in a given range of temperature. Also, this work shows that complex processes cannot be fully understood or even monitored accurately without using a proper combination of independent techniques.

A devastating rainfall in Tuscany in November 2012 provided the opportunity to study the diffusion of As and Sb along the Tafone mining area, under extreme conditions, by comparing their concentrations in water, soil, and river sediments in drought (equilibrium) periods against those observed immediately after a flooding event and after a period of 6 weeks rebalancing of the watercourse. The data obtained at equilibrium show a significant “natural” As and Sb contamination with the highest levels along the valley in the mine surroundings. Very high Sb and As concentrations in the sediment of the Tafone Lake cause a potential continuous supply of toxic elements to the river downstream. In surface waters (river water and lake), As concentrations exceed slightly, and only occasionally, the Italian regulatory limits, while, those for Sb are always widely exceeded. In addition, the soils collected along the Tafone valley show high Sb and As total content, and were studied by a novel nine-step sequential extraction protocol, proposed for assessing the bioavailability of As and Sb in sulphide ore mining-impacted soils. Experimental data show that As and Sb mobility is strongly affected by even small variations of the pH and redox conditions, thus controlling their release into the environment. The results obtained after the flood demonstrated that extreme weather events can induce two main problems: (1) the temporary increase of As and Sb amount transported by the river water to the sea, principally as particulate and colloidal material, and (2) the sediment transport out the mining area, reaching soils eventually used for agriculture, and the potential diffusion through the food chain.

•A novel OPC-equipped low-cost device for airborne PM monitoring and sampling.•The EU Civitavecchia maritime hub (Roma, Italy) as the site for the test campaign.•A new PM data correction strategy for relative humidity is proposed and discussed.•Spectroscopy investigations show microplastics within airborne PM.•This low-cost device is an up-to-date real-time air quality monitoring approach.

High-temperature Fourier transform infrared (HT-FTIR) spectroscopy was used to characterize the deprotonation process of synthetic potassic-ferro-richterite of composition A(K0.90Na0.07)B(Ca0.54Na1.46)cFe4.222+Fe0.783+TSi8O22WOH1.70O0.302−$ ^{\rm{c}}{\left( {{\rm{Fe}}_{4.22}^{2 + }{\rm{Fe}}_{0.78}^{3 + }} \right)^{\rm{T}}}{\rm{S}}{{\rm{i}}_8}{{\rm{O}}_{22}}^{\rm{W}}\left( {{\rm{O}}{{\rm{H}}_{1.70}}{\rm{O}}_{0.30}^{2 - }} \right)$. Unpolarized single-crystal spectra were collected both in situ and on quenched samples, and heating experiments were conducted in air, at a rate of 10 °C/min. The room-T spectrum measured before annealing shows a main band at 3678 cm-1and a minor band at 3622 cm-1; these are assigned to local configurations involving Fe2+at M(1)M(1)M(3) and facing a filled and an empty alkali-site, respectively. At 400 °C, a new band grows at 3656 cm-1; this is the most intense feature in the pattern at 450 °C. At T≥ 500 °C, all peaks decrease drastically in intensity, and finally disappear at T> 600 °C. The total absorbance measured in situ increases significantly in the 25 < T< 450 °C range, although the spectra collected on quenched samples show no OH loss in the same Trange. This feature is consistent with an increase of the absorption coefficient (ε) with T, the reason for which is still unclear. However, this feature has significant implications for the quantitative use of FTIR data in HT experiments. Examination of the relevant OH-stretching bands shows that iron oxidation occurs preferentially at the M(1,3) sites associated with occupied Asites. The deprotonation temperature indicated by FTIR for single-crystals is around 100 °C higher that that obtained by HT-X-ray diffraction (XRD) on single crystal by Oberti et al. (2016), whereas that obtained by HT-XRD on powders is intermediate. This unexpected observation can be explained by considering that: (1) the iron oxidation process, which is coupled to deprotonation and is probed by XRD, occurs preferentially at the crystal surface where it is triggered by the availability of atmospheric oxygen; (2) the proton diffusion, probed by FTIR, is slower that the electron diffusion probed by XRD; thus, the temperature shift may be explained by a much longer escape path for H in single-crystals than in powders. These results suggest that possible effects due to crystals size should be carefully considered in HT experiments done on Fe-rich silicates.

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 low-wavenumber (<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.

A simple compact temperature sensor and microheater in a wide temperature range has been developed, realizing a laser-patterned resistive structure on the surface of a synthetic polycrystalline diamond plate. Imaging and spectroscopy techniques used to investigate morphology, structure, and composition of the pattern showed that it incorporates different nondiamond carbon phases. Transport experiments revealed the semiconducting behavior of this microresistor. Thermal power measurements versus temperature are presented. A possible application of this device that may easily match compact experimental layouts avoiding both thermal anchoring offset and mechanical stress between sample and sensor is discussed. The patterned structure undergoes testing as a microthermometer, providing fast response and excellent stability versus time. It exhibits a good sensitivity that coupled to an easy calibration procedure minimizes errors and guarantees high accuracy. Plot of temperature versus input power of the resistive patterned line used as microheater shows a linear behavior in an extended temperature range.

In order to clarify details of volatiles incorporation in arrojadites, two samples previously 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 NH4+ 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 NH4+ 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/Fe2+ 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 inthe case of low-Z elements. Assuming the water content derived from EMP analysis, an integrated molar coefficient (polarized data) eI = 63937 l/(mol·cm2) is calculated for the spectroscopic quantification of H2O in arrojadite. For N, based on the EMP analysis, we obtain (for unpolarized data in the N-O bending region) ei = 11000 ± 2000 l/(mol cm2) and eI = 300±60 l/(mol·cm2) from integrated and linear intensity data, respectively.

This work relates the occurrence and the characterization of fibrous tremolite within the latest pyroclastic deposits of the Colli Albani (Alban Hills) volcano, to the south-east of Rome (Italy). These mineralizations were observed during a systematic rock sampling undertaken to complete the geological survey for the new 1:50,000 map of this volcanic area. The examined specimens were collected inside distal deposits correlated to the last Albano Maar activity, which are geographically located within the boundaries of the Nemi community. Tremolite occurs within both carbonate ejecta and the host pyroclastic rocks. It shows up as whitish to light grey-coloured aggregates of crystals with fibrous aspect and sericeous brightness. Due to the extremely small crystal dimensions, never exceeding 0.5 μm in diameter, the micro-chemical composition of the fibres could be obtained only by combining P-XRD, SEM–EDX and FTIR methods. Infrared spectroscopy, in particular, proved to be a valuable technique to characterize the studied amphibole. The composition determined is that of a Fe-free F-rich (c. 53 %) tremolite with significant (c. 20 %) richterite components in solid solution. The occurrence of fibrous tremolite in an inhabited place, occurring as natural geological material rather than being due to anthropogenic pollution, should be examined with concern, because it implies complex health and legal responsibilities in the case of mobilization due to extreme climatic events.

Actinolite and glaucophane are the principal amphiboles in greenschist- and blueschist-facies metamafic rocks, respectively, and constitute an important mineral pair for deducing the conditions of medium- and high-pressure metamorphism. Here we present the crystal-chemical properties of amphiboles synthesized along the tremolite-glaucophane join as an important starting point for the more chemically complex samples occurring in nature. Amphiboles were synthesized in 10 mol% increments at conditions ranging from 840 °C and 0.6 GPa for tremolite-rich to 750 °C and 2.5 GPa for glaucophane-rich amphiboles. The amphibole yields were generally high (~95 wt%), though minor quartz, pyroxene, and amorphous material (either glass or quenched solute) were often present. Electron microprobe analysis of the amphibole showed that deviations from the nominal or intended compositions occurred, with the observed compositions showing solid solution primarily toward the katophorite component and reaching a maximum near the middle of the join. Unit-cell dimensions showed a pronounced positive deviation from ideality, even after (linear) correction for the non-join components, suggesting a strong tendency toward exsolution. Single-crystal refinements of a couple of selected amphiboles confirmed the deviation from nominal composition and confirmed the presence of ANa, TAl, and CAl, the latter disordered between the M(2) and M(3) sites. Infrared spectra in the OH-stretching region were measured on samples that were heated to 250-350 °C to remove absorbed moisture. The spectra consist of a main band centered in the 3675-3660 cm-1region and two minor absorptions on both sides of the dominant central peak, which are centered at 3720 and 3640 cm-1and can be attributed to OH next to ANa and CAl, respectively. The main band is evidently composed of several overlapping components due to local arrangements of B cations typical of tremolite, CaCa, glaucophane, NaNa, and cummingtonite, MgMg. Examination of several intermediate amphiboles by both single-crystal XRD and by high-resolution TEM analysis could not identify evidence of reflections or ordered domains that would violate the C2/m symmetry of the end-member amphiboles. Comparing the compositions of the synthetic amphiboles from this study with winchite-rich amphiboles in nature shows that deviations from the tremolite-glaucophane join are common. The inability to make pure winchite or even winchite-rich amphiboles on the tremolite-glaucophane join suggests that this structure is unstable.

This paper reports on the occurrence and the crystal structure of kircherite, a new member of the cancrinite-sodalite group of minerals from Valle Biachella, Sacrofano community (Rome, Latium, Italy). The mineral occurs in association with sodalite, biotite, iron oxides, titanite, fluorite, and a pyrochlore-group mineral. The groundmass of the ejectum consists essentially of K-feldspar with subordinate plagioclase. Kircherite (3 mm as largest size) is observed within miarolitic cavities of the rock and typically occurs as parallel associations of hexagonal, thin, tabular colorless to light-gray transparent crystals; it is non-pleochroic and uniaxial negative, with ω = 1.510(2) and ε = 1.502(2). Dcalcis 2.457 g/cm3. Kircherite is trigonal with a = 12.8770(7), c = 95.244(6) Å, V = 13677(1) Å3, Z = 1. The structure has been refined in the trigonal space group R32, obtaining a R-value of 8.5% on 8131 reflections with I/σI > 2. The strongest seven reflections in the X-ray powder pattern are [d in Å (I %) (hkl)]: 3.717 (100) (3 0 0), 2.648 (100) (2 1 28; 0 0 36), 3.232 (65) (2 1 19), 3.584 (60) (1 2 14), 3.604 (53) (1 0 25), 3.799 (52) (1 2 11), 3.220 (38) (2 2 0). The single-crystal FTIR spectrum rules out OH groups and shows the presence of H2O and CO2molecules in the structural cages of the mineral. Chemical analysis gives (in wt%): SiO232.05, Al2O327.13, FeO 0.07, K2O 4.38, CaO 8.75, Na2O 13.62, MgO 0.01, MnO 0.02, TiO20.01, SO3 12.87, Cl 0.35, F 0.05, total 99.82. The empirical formula calculated on the basis of Σ(Si+Al) = 216 apfu is (Na89.09Ca31.63K18.85Fe0.20Mn0.06Mg0.05Ti0.03)Σ=139.91[(Si108.13Al107.87)Σ=216.00O430.00](SO4)32.58Cl2.00F0.53⋅6.86H2O, which corresponds to the ideal formula [Na90Ca36K18]Σ=144(Si108Al108O432)(SO4)36⋅6H2O.

AbstractThe symmetry and crystal chemistry of a (OH,F)-rich spessartine from Junzico Xijang, Wushan Spessartine Mine, Yunxiao Co., Fujian Province, P.R. China, with composition X(Mn2+2.87Fe2+0.09Ca0.04) Y(Al1.94Fe3+0.06) Z[(SiO4)2.52(OH1.11F0.81)] have been studied by single-crystal X-ray structure refinement and FTIR spectroscopy. This sample is tetragonal, space group I41/acd, with a = b = 11.6347(3) Å, c= 11.6449(3) Å, c/a= 1.006, Rall3.1% (θmax= 55°). The two independent tetrahedra differ significantly both in terms of refined bond-lengths and site-scattering values, the latter allowing to confirm the extent of the (OH,F) substitution and to its preferential ordering at O3, the site occupied by the anions coordinated to Z2. FTIR spectra consist of a prominent peak at 3568 cm–1and a doublet at 3622–3632 cm–1. Pleochroic curves suggest assignment to a unique O—H dipole, involved in two different hydrogen bonds (O3—H···O2 and O3—H···O3, the latter showing two different, O—H···H and O—H···F, configurations). The observed space group and composition imply: (a) that lowering in symmetry is related to the presence of (OH,F)4groups; (b) the existence of a new hydrogarnet end-member with ideal composition XMn3YAl2Z[(SiO4)2(OH)4] and significant F content, the first related to the pyralspite series; the sample of this work is close to its 50:50 solid solution with spessartine. Geometric considerations and the very limited increase in volume with respect to spessartine suggest that the presence of F is a requisite for the incorporation of significant amount of monovalent anions in pyralspites.

AbstractThe structural characterization of whiteite-(CaFeMg), a natural orthophosphate from Crosscut Creek, Yukon, Canada, with chemical composition (Ca0.86Na0.05)Σ = 0.91(Fe0.88Mn0.02)Σ = 0.90Mg2.17Al1.93(PO4)4(OH)2· 8 H2O obtained by WDS-EMPA, was carried out by means of single crystal X-ray diffraction. The structure was solved in the P2/amonoclinic space group, with the following unit cell constants: a= 14.8700(15), b= 6.9785(5), c= 9.9268(10) Å, β= 110.110(1)°, V= 967.31(15) Å3. Structure refinement lead to the crystal chemical formula (Ca0.95Na0.11)Σ = 1.06Fe0.90Mg2.01Al2.05(PO4)4(OH)1.99· 8.17 H2O. Phosphorus atoms display tetrahedral (PO4) coordination, while magnesium, iron(II) and aluminum display regular octahedral coordination; calcium displays a complex CaO8coordination. MgO2(H2O)4, FeO6, AlO4(OH)2, CaO8polyhedra and PO4 groups are arranged such as to form a three-dimensional framework via edge- and vertex-sharing arrangements. Strong O—H … O hydrogen bonds contribute to stabilize the array: such interactions were also investigated by means of Libowitzky formula (Libowitzky, 1999) application, owing to the results of IR spectroscopy.

AbstractNonstoichiometric REEAl2.07(B4O10)O0.60(REE= La, Pr) borates have been crystallized and analyzed by means of single crystal X-ray diffraction. The compounds resulted to be isostructural within hexagonal space group P-62m(n. 189), with the following unit cell parameters: a= 4.6170(1) ÅÅ, c= 9.3640(3) ÅÅ and V= 172.87(1) ÅÅ3(La); a= 4.5990(1) ÅÅ; c= 9.3270(2) ÅÅ and V= 170.87(1) ÅÅ3(Pr). REEcations make up a trigonal prismatic coordination, by means of six REE-O bonds under 2.5 ÅÅ; aluminium cation is five-coordinated, displaying a square pyramidal coordination, while the boron atom forms BO4tetrahedral units. The present borates belong to the structural type of NdAl2.07(B4O10)O0.60dimetaborate [1]: thus, the three-dimensional framework can be described as a structure packed down crystallographic axis c, with layers of six-membered rings of B tetrahedra alternated by inter-layers REEcations and layers of Al polyhedra. An intricate network of Al······O and REE······O interactions complete the array.

Mesoporous and dense sol−gel titania films have been synthesized and processed in similar conditions to make a comparative study of crystallization to anatase in porous and dense samples. We have performed a correlative analysis combining THz spectroscopy with synchrotron radiation, variable angle incidence infrared spectroscopy, spectroscopic ellipsometry and grazing incidence X-ray diffraction to characterize the structure of titania films as a function of thermal processing conditions. THz spectra have shown that small anatase crystalline clusters are already present in the as-deposited samples, and both crystallization and growth process are favored in the mesoporous films. Moreover, the analysis by X-ray diffraction and variable angle incidence infrared spectroscopy has allowed identification of the presence of small textures in the samples.

Eleven compositions along the join Na(NaMg)Mg5Si8O22(OH)2-Na(NaCa)Mg5Si8O22(OH)2(“magnesiorichterite”-richterite) have been synthesized at T = 800-850 °C and PH₂O= 0.35-0.5 GPa. The run products have been characterized by electron probe microanalysis (EPMA), synchrotron and conventional X-ray powder diffraction (XRPD), Fourier transformed infrared (FTIR) spectroscopy, and selected area electron diffraction (SAED-TEM). Nominally, the chemical variation along the join can be expressed as BMgxBCa1-xwith 0 ≤ x ≤ 1. A combination of EPMA and FTIR data in the OH-stretching region show that a complete solid solution is obtained under the conditions used. Nevertheless, a slight deviation from the nominal compositions involving a limited loss of Na at A and B sites, balanced by an increase of Ca at the B site, is present. Several indications of a displacive and coelastic P21/m → C2/m transformation induced by the Ca-Mg chemical substitution are observed. The phase transition occurs at B-site composition (Xc) close to B(Na1Mg0.7Ca0.3). C2/m samples with a Ca content of 0.34, 0.45, and 0.54 apfu show a significant strain tail related to local compositional inhomogeneities. This residual strain disappears as the amount of BCa significantly increases with respect to that of BMg. The transformation behavior observed here mirrors that of pyroxenes along the join diopside (CaMgSi2O6)-enstatite (Mg2Si2O6). The cell parameters of amphiboles with CMg5, TSi8, and W(OH)2and variable A- and B-site populations follow almost linear and continuous trends, indicative of small amounts of spontaneous strain accompanying these monoclinic phase transitions and the absence of significant miscibility gaps among different amphibole groups when quenched from higher temperatures of crystallization.

AbstractNonstoichiometric REEAl2.07(B4O10)O0.60(REE= (La, Ce); Ce; Nd) dimetaborates have been crystallized and analyzed by means of single crystal X-ray diffraction. The compounds resulted to be isostructural within hexagonal space group P-62m(n. 189), with the following unit cell parameters: a= 4.6060(6) Å, c= 9.3510(8) Å and V= 171.81(3) Å3; (La, Ce); a = 4.5960(6) Å; c= 9.3170(10) Å and V= 170.44(4) Å3(Ce); a= 4.5830(7) Å, c= 9.2810(14) Å and V= 168.82(4) Å3(Nd). The REEcations are surrounded by six oxygen atoms, making up a trigonal prismatic coordination; Al cation is surrounded by five oxygen atoms, resembling a square pyramidal coordination, while the BO4group displays tetrahedral arrangement. The three-dimensional framework can be described as a mica-like structure packed down crystallographic axis c, with layers of six-membered rings of B tetrahedra alternated by inter-layers REEcations and layers of Al polyhedra. A complex network of REE… O and Al … O interactions concur to stabilize the framework.

The P21/m ? C2/m phase-transition has been studied by high-T FTIR analysis on a series of synthetic amphiboles in the Li2O-Na2O-MgO-SiO2-H2O (LNMSH) system. Spectra were collected in the T range 25-450 °C on KBr disks. All examined amphiboles have P21/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 (Tc), 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. Tc 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 Tc 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 HT-XRD (high-T X-ray diffraction). They correlate linearly with the aggregate cation radius at M(4) [Tc (°C) = 803-533 rM(4); R2 = 0.97]. This work thus provides a measure of the role played by the size of the M(4) polyhedron in determining the Tc 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.

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 Cr2O3 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 Å) 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 H2O vibrations in the crystals. The polarised FTIR spectra collected with E?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 ?3 antisymmetric stretching, and ?1 symmetric stretching modes of type II 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 ei = 27126 l * mol-1 * cm-2 from the calibration curve of Libowitzky & Rossman (1997), a water content of ~ 30 ppm is derived for the studied emerald.

Abstract: The study of volatile constituents in minerals has potential applications ranging from environmental studies to ore research to volcanic hazards. In this paper we present new data on the volatile (particularly CO2) content of a series of feldspathoids belonging to the cancrinite-sodalite group of minerals, in combination with other data collected over the last few years. The work has been essentially done using FTIR microspectroscopy to detect and characterize the speciation of H and C in the micropores of these minerals. We show that most cancrinite-sodalite group of minerals are able to trap CO2 in their structure in addition to other molecular and anionic species such as H2O, OH, F, Cl, SO4, SO3 etc. A combination of in situ and annealing heat-treatments shows that the different species in the cancrinite-sodalite group release CO2 at different temperatures, due to the different connectivity of their pores. Detailed FTIR microspectrometry mappings typically show non-homogeneous distributions of hydrogen and carbon across the samples, and suggest a possible use of these minerals as a tool for geothermometric modelling. The finding that most cancrinite-sodalite group minerals are able to trap carbon dioxide opens a new frontier in the design of materials having potential for carbon sequestration from the atmosphere.

This paper describes a multi-technique approach to the complete crystal-chemical characterization of a gadolinite-(Y) sample found in a volcanic holocrystalline ejectum near the Vico lake (Latium, Italy). Gadolinite-(Y) occurs as poly-twinned crystals forming rounded short-prismatic aggregates (generally 0.1-0.3 mm in size, with the largest ever found >1 mm), associated with zircon, thorite, danburite, betafite, and tourmaline. Both the chemical and the structural characterization of gadolinite-(Y) from Vico required nonstandard procedures. After correction for (100) twinning, the structure of a crystal with unit-cell dimensions a = 4.7708(4) Å, b = 7.6229(7) Å, c = 9.8975(9) Å, β = 90.017(7)°, and V = 359.95(6) Å3was refined in the P21/c space group down to R = 2.3%. Electron microprobe (EMP) analyses failed to give accurate quantification of major elements, due to the presence of light and volatile elements as well as of rare earth elements (REE) and actinides. Secondary ion-mass spectrometry (SIMS) analysis done with accurate calibrations on well-characterized minerals allowed quantification of light, volatile, REE, and actinide elements, and also of Ca and Si. The derived chemical composition was interpreted with reference to the site-scattering values obtained from single-crystal structure refinement. The resulting unit formula is (Ca0.81REE0.66Y0.39Th0.13U0.02)Σ2.01(Fe2+0.29Li0.14Fe3+0.12Mn0.02Mg0.01)Σ0.58(Si1.98Be1.09B0.81Li0.12)Σ4.00O8(O1.20F0.51OH0.29)Σ2.00, which yields a calculated density of 4.267 g cm-3. Fourier transform infrared spectroscopy (FTIR) single-crystal spectrum of gadolinite-(Y) shows several absorptions in the OH-stretching region that can be assigned to the different local configurations involving Ca and (REE,Y) at the A site and Be, B, and Li at the Z site. Lithium incorporation in gadolinite-group minerals is proposed to occur according to the exchange vectors: (1) XFe2++ AY → XLi + A(Th +U) and (2) ZBe + XFe2+→ ZLi + XFe3+; the maximum amount of Li allowed in the gadolinite structure is 1.0 apfu. This work provides the first evidence that Li is a significant component in gadolinite-group minerals, particularly in geochemical environments enriched in actinides. This conclusion suggests that materials having the composition of Li-rich gadolinite may be considered as possible forms for radioactive waste disposal.

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 [6]Altot~0.55 atoms per formula unit (apfu), [6]Ti ~0.45 apfu, and [6]Fe3+~0.40 apfu. SIMS and SREF data show all samples to have an O3 anion composition of OH ≈ O2-≈ 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: ~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-O2-at the O3 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 M1Ti4+or M1Fe3+M3Fe3+are associated with O2-at both adjacent O3 sites, and that M3Al is locally associated with OH, confirming SRO models based on structure refinement results.

Abstract: This paper describes the first occurrence of datolite in a volcanic ejectum collected at Pitigliano, Vulsini volcanic complex, Toscana, Italy. The studied specimen was sampled within the pyroclastic levels erupted during one of the several eruptive phases of the Latera caldera in the Roman Comagmatic region (253–166 ka). The host rock is massive, with a syenitic appearance, and consists of predominant sanidine, both as fine-grained groundmass and phenocrystals up to 1 cm long. Associated minerals are andraditic garnet, clinopyroxene (augite), biotite, iron oxide and vishnevite. Datolite occurs within vugs in the ejectum as well-formed, transparent, colourless crystals, with stubby prismatic shape; the crystals are about 0.5 mm in maximum diameter. The crystal structure of datolite from Pitigliano has been refined in theP21/c space group to R=2.18%. Cell dimensions are:a(Å)=4.8318(4),b(Å)=7.6116(3),c(Å)=9.6380(2),β(o)=90.141(4),V(Å3)=354.46(3). The chemical composition is (Ca2.006K0.001)Σ2.007 (Fe0.007Mn0.004Mg0.002)Σ0.013 (B1.986Si1.988Al0.026)Σ4.000O8 (OH1.962O0.026F0.012)Σ2.000 and the density calculated on the basis of composition and cell dimensions is Dc=3.00 g/cm3.

This work reports the crystal-chemical characterization of Mn-rich amphiboles from the Grenville Marble of the Arnold mine, Fowler, St. Lawrence Co., New York (U.S.A.), which were previously described by Benimoff et al. (1991) as “manganoan silicic edenite”. According to the new nomenclature scheme for monoclinic amphiboles (Leake et al. 2004) the ideal composition of reference, ANa B(CaMn) CMg5T(Si7Al)O22(OH)2with Ca > 1 apfu, is an end-member of the newly defined Group 5, and is named parvo-mangano-edenite. Re-examination of the original rock specimen showed significant inter- and intra-crystalline compositional variations, which can be expressed by the ANa-1TAl-1A⃞ 1TSi1and BMn2BCa-2exchange vectors. The first vector leads to parvo-manganotremolite, ideally A⃞ B(CaMn)CMg5TSi8O22(OH)2with Ca > 1. The second mechanism was never found to reach Mn dominance; however, crystal-chemical analysis does not provide any evidence of structural limits, and thus the magno-calcic counterparts of the Group 5 amphiboles of this work may occur in similar but Mn-richer genetic environments. The presence of Mn at the B site helps to stabilize the charge arrangement of edenite. The parvo-mangano-edenite crystal with composition closest to the end-member, i.e., A(Na0.74K0.02)B(Ca1.27Mn0.73)C(Mg4.51Mn2+0.28Fe2+0.05Fe3+0.03Al0.12Ti0.01)T(Si7.07Al0.93)O22(OH)2, has a = 9.8260(5), b = 18.0487(9), c = 5.2840(4) Å, β = 104.55(1)º, V = 907.1 Å3(Z = 2); the calculated density is 3.11 g/cm3. The parvo-mangano tremolite crystal, with composition A(Na0.44K0.01)B(Ca1.13Mn0.83Na0.04)C(Mg4.69Mn2+0.21Fe2+0.03Fe3+0.01Al0.06)T(Si7.52Al0.48)O22(OH)2, has a = 9.7807(5), b = 18.0548(9), c = 5.2928(4) Å, β = 104.19(1)º, V = 906.1 Å3(Z = 2); the calculated density is 3.08 g/cm3. The different compositions are virtually indistinguishable under the optical microscope, but can be identified by a measure of their unit-cell parameters. The single-crystal FTIR spectrum of parvo-mangano-edenite in the OH-stretching region shows two main absorptions at 3711 and 3671 cm-1, plus shoulders at 3695, 3660, and 3641 cm-1, respectively. FTIR spectroscopy indicates extensive short-range-order of cations in these amphiboles.

This paper describes a high-pressure synchrotron infrared (Ir) spectroscopy study of the synthetic amphibole Na(NaMg)Mg5Si8O22(Oh)2. This compound has P21/m symmetry at room conditions; its IR OH-stretching spectrum consists of two main bands at 3743 and 3715 cm-1, which are assigned to the two symmetrically independent O-H groups in the P structure (sample 403, Iezzi et al. 2004a). For increasing pressure, both bands shift toward higher frequency, suggesting a shortening of the O-H bond. In addition, the two bands progressively merge to give a single, symmetric and broad absorption band at 20-22 Gpa. This behavior suggests that at 20-22 Gpa there is a unique O-H group in the structure, indicative of a C-lattice type. The Ir data thus show that the examined sample undergoes a P21/m ↔ C2/m phase-transition at that pressure. Upon release of pressure, the initial two-band pattern is immediately recovered indicating that the pressure-induced phase-transition is reversible, as already observed for the same kind of transition induced by temperature. By analogy with structurally related pyroxenes, and taking into account the possible crystal structural topologies of amphiboles, we suggest that the C2/m polymorph stable at high pressure is characterized by fully kinked double-chains.

We describe here the synthesis of amphiboles along the nominal Na(NaMg)Mg5Si8O22(OH)2- Na(LiMg)Mg5Si8O22(OH)2join, at 800 °C, 0.4 GPa. High amphibole yields (>90%) plus minor quartz and enstatite have been obtained at all compositions; amphibole crystals are acicular and their size rarely exceeds 20-30 × 0.5-3 μm. TEM analysis shows the presence of h+k odd reflections in all samples, indicative of a P-lattice. By similarity with closely related amphiboles from the literature (e.g., Oberti et al. 2000; Cámara et al. 2003) a P21/m space group was assigned to the amphiboles synthesized here. Refined cell-parameters from X-ray powder-patterns show a linear decrease as a function of increasing Li at M4, a and β being the most affected parameters. The four infrared OH-stretching spectra all show two main bands at 3741-3748 and 3712-3716 cm-1, respectively. They are assigned to two independent O-H groups in the P21/m structure, interacting with a strongly delocalized ANa. The spectra show in addition two minor absorptions at about 3688 and 3667 cm-1, respectively; these bands are assigned to vacant A-sites in the structure and indicate slight departure of the nominal composition toward cummingtonite. The present work shows that one apfu of BNa can also be completely replaced by one apfu of BLi (M+), in synthetic Na(M+Mg)Mg5Si8O22(OH)2, and that all compositions have P21/m symmetry at ambient conditions.

Abstract: 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 ANa0.8B(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.

Abstract A series of amphiboles along the magnesioriebeckite—?Na2Mg3Fe3+2Si8O22(OH)2– ferri-clinoholmquistite—?Li2Mg3Fe3+2Si8O22(OH)2 - join, defined by the BLiB Na-1 exchange vector, were hydrothermally synthesized at 700°C, 0.4 GPa, NNO + 1 redox conditions. Powder XRD and SEM-EDAX showed a very high (> 90%) amphibole yield for all samples. X-ray patterns were indexed in the C2/m space group; refined cell-parameters show a linear decrease of a and ß as a function of chemistry. IR spectra in the OH-stretching region show four main and rather sharp bands; these are assigned to Mg and Fe2+ at M(1,3), and indicate that the obtained amphiboles depart from the nominal octahedral composition (M1,3Mg3). The IR spectra also show that there is an increasing filling-up of the A-site for increasing Na in the system (increasing solid-solution toward, arfvedsonite). Mössbauer spectra show four well-defined quadrupole doublets which are assigned to Fe3+ at M2 and to Fe2+ at M1, M3 and M4, respectively. The Fe3+/Fe2+ content derived from fitted peak areas show variable Fe3+ concentration along the series. Mössbauer spectra also show a distinct alteration of 57Fe hyperfine parameters with changing Na–Li at M4. The most evident variation is observed for the quadrupole splitting of Fe3+ at M2, which increases by ˜50% from ferri-clinoholmquistite to magnesio-riebeckite; this suggest that the M2 octahedron in ferri-clinoholmquistite is much closer to the ideal geometry than the M2 octahedron in magnesio-riebeckite. Mössbauer spectra show also a well-defined increase in the Fe2+ quadrupole splitting of the M1 and M3 octahedra, which is attributed to the Na–Li distribution at the B-sites.

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⊥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 O(11)–H(1) dipole is OH∧c~35°, in excellent agreement with the neutron data of Lager et al. (Can Mineral 37:763, 1999). A SIMS-based calibration curve at ~10% rel. accuracy has been worked out and used as reference for the quantitative analysis of H2O in vesuvianite by FTIR. Based on previous SIMS results for silicate minerals (Ottolini and Hawthorne in J Anal At Spectrom 16:1266, 2001; Ottolini et al. in Am Mineral 87:1477, 2002) the SiO2 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 H2O 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 ɛi=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.

Synthetic NaNa2Mg5Si8O21(OH)3is the first triclinic member of the amphibole group, and has a tripling of the unit cell in the b direction. The space group is C1̄ and the triple-b repeat gives Z = 6. The unit-cell parameters are: a = 9.883(2), b = 54.082(9), and c = 5.277(1) Å, α = 90.045(4)°, β = 103.068(3)°, γ = 89.960(4)°, and V = 2748(1) Å3. The crystal structure has been refined to R1= 7.6 and wR2= 16.7% for the 1835 reflections with Fo> 4σFand for 4832 supercell reflections in the 2θ range 2-25°, respectively. The structure is pseudo-monoclinic, but both the intensity distribution and refined model indicate space group C1̄. Compared with the common C2/m amphibole structure, the two halves of an I-beam unit are no longer mirror-related, and the overall structure can be rationalized in terms of two different types of I-beam occurring in the unit cell. The first (with multiplicity 2) is centrosymmetric, and the second (with multiplicity 4) is non-centrosymmetric. There are also significant displacements of the cations, especially at the M4 sites, from their corresponding locations in the C2/m structure. The correlated displacements of Na atoms at the M4 sites permit incorporation of excess protons in pseudo-tetrahedral cavities between two adjacent chains of tetrahedra belonging to different I-beams. Bond-valence calculations and crystal-chemical analysis suggest that excess protons are bonded to O atoms at the O4 sites, and are hydrogen bonded to O atoms at adjacent O2 sites. The infrared spectrum of the amphibole in the principal OH-stretching region has a triplet of sharp bands at 3740, 3727, and 3711 cm-1, which are assigned to the three independent “normal” O3-H groups in the triclinic structure. There is an additional intense and very broad absorption at 3430 cm-1that is resolved only when adsorbed moisture is removed. This band is assigned to the extra H in the structure. All the details provided by structure refinement and the proposed location of the excess H atoms is in accord with previous HRTEM and 29Si- and 1H MAS NMR studies of this amphibole.

Synthetic NaNa2Mg5Si8O21(OH)3is the first triclinic member of the amphibole group, and has a tripling of the unit cell in the b direction. The space group is C1̄ and the triple-b repeat gives Z = 6. The unit-cell parameters are: a = 9.883(2), b = 54.082(9), and c = 5.277(1) Å, α = 90.045(4)°, β = 103.068(3)°, γ = 89.960(4)°, and V = 2748(1) Å3. The crystal structure has been refined to R1= 7.6 and wR2= 16.7% for the 1835 reflections with Fo> 4σFand for 4832 supercell reflections in the 2θ range 2-25°, respectively. The structure is pseudo-monoclinic, but both the intensity distribution and refined model indicate space group C1̄. Compared with the common C2/m amphibole structure, the two halves of an I-beam unit are no longer mirror-related, and the overall structure can be rationalized in terms of two different types of I-beam occurring in the unit cell. The first (with multiplicity 2) is centrosymmetric, and the second (with multiplicity 4) is non-centrosymmetric. There are also significant displacements of the cations, especially at the M4 sites, from their corresponding locations in the C2/m structure. The correlated displacements of Na atoms at the M4 sites permit incorporation of excess protons in pseudo-tetrahedral cavities between two adjacent chains of tetrahedra belonging to different I-beams. Bond-valence calculations and crystal-chemical analysis suggest that excess protons are bonded to O atoms at the O4 sites, and are hydrogen bonded to O atoms at adjacent O2 sites. The infrared spectrum of the amphibole in the principal OH-stretching region has a triplet of sharp bands at 3740, 3727, and 3711 cm-1, which are assigned to the three independent “normal” O3-H groups in the triclinic structure. There is an additional intense and very broad absorption at 3430 cm-1that is resolved only when adsorbed moisture is removed. This band is assigned to the extra H in the structure. All the details provided by structure refinement and the proposed location of the excess H atoms is in accord with previous HRTEM and 29Si- and 1H MAS NMR studies of this amphibole.

In the present work, we characterize the amphibole Na(NaMg)Mg5Si8O22(OH)2synthesized at 0.4 GPa and 750, 800, and 850 °C, and 0.5 GPa, 900 °C. Experiments at 800 and 900 °C yielded crystals suitable for single-crystal data collection. Structure refinement shows that synthetic Na(NaMg)Mg5Si8O22(OH)2has P21/m symmetry at room T. The two non-equivalent tetrahedral double-chains differ in their degree of stretching and kinking. The infrared spectrum of synthetic Na(NaMg)Mg5Si8O22(OH)2has two well-defined absorption bands at 3742 and 3715 cm-1which can be assigned to O-H bands associated with the two independent anion sites (O3A and O3B) in the structure. The higher frequency band is assigned to the shorter O3B-H2 bond, and the lower frequency band is assigned to the longer O3A-H1 bond. The broader shape of the 3743 cm-1band is consistent with a stronger interaction of the H2 atom with ANa, which is confirmed by structure refinement. Increasing T of synthesis causes a progressive departure from the ideal stoichiometry via the A⃞1BMg1ANa-1BNa-1substitution, as confirmed by EMPA, structure refinement, and FTIR spectroscopy.

In the present work, we characterize the amphibole Na(NaMg)Mg5Si8O22(OH)2synthesized at 0.4 GPa and 750, 800, and 850 °C, and 0.5 GPa, 900 °C. Experiments at 800 and 900 °C yielded crystals suitable for single-crystal data collection. Structure refinement shows that synthetic Na(NaMg)Mg5Si8O22(OH)2has P21/m symmetry at room T. The two non-equivalent tetrahedral double-chains differ in their degree of stretching and kinking. The infrared spectrum of synthetic Na(NaMg)Mg5Si8O22(OH)2has two well-defined absorption bands at 3742 and 3715 cm-1which can be assigned to O-H bands associated with the two independent anion sites (O3A and O3B) in the structure. The higher frequency band is assigned to the shorter O3B-H2 bond, and the lower frequency band is assigned to the longer O3A-H1 bond. The broader shape of the 3743 cm-1band is consistent with a stronger interaction of the H2 atom with ANa, which is confirmed by structure refinement. Increasing T of synthesis causes a progressive departure from the ideal stoichiometry via the A⃞1BMg1ANa-1BNa-1substitution, as confirmed by EMPA, structure refinement, and FTIR spectroscopy.

Amphiboles were hydrothermally synthesized at 500 °C and 4 kbar in the system Li2O-Na2OFeO- Fe2O3-SiO2-H2O, with nominal compositions along the riebeckite [□Na2Fe32+Fe23+Si8O22(OH)2]-ferri-clinoferroholmquistite [□Li2Fe32+Fe23+Si8O22(OH)2] join, where the exchange vector is NaLi-1 at the B-site. Experimental products were characterized by powder XRD and SEM-EDAX, confirming very high amphibole yield along the join (>95%, plus minor quartz). The XRD patterns can be indexed in C2/m, and the refined cell parameters show linear variation as a function of composition. For the BLi end-member, the IR spectrum shows a single sharp main band centered at 3614 cm-1, which is assigned to the FeFeFe-OH-A□ configuration. With increasing BNa in the mineral, this band broadens and shifts 4 cm-1to higher frequencies. This effect can be attributed to the change in M4 site occupancy. Minor ANa (partial solid-solution toward arfvedsonite) is also observed with increasing sodium in the system. Mössbauer spectroscopy confirms the cation distribution provided by IR data, and shows that a small, but significant amount of Fe2+occurs at M4 along the join. Infrared spectroscopy shows that the Li end-member has a very ordered structure, whereas intermediate compositions show local heterogeneities associated with the presence of two different B sites occupied by Na or Li.

Two new minerals of the hellandite group were found within alkali-syenitic ejecta enclosed in pyroclastic formations of the Roman Comagmatic Province (Latium, Italy). Mottanaite-(Ce) [ideally XCa4Y(CeCa)ZAlTBe2(Si4B4O22)WO2] and ciprianiite [ideally XCa4Y[(Th,U)(REE)]ZAlT⃞2(Si4B4O22) W(OH, F)2] occur as transparent, brown-colored, tabular euhedral crystals in miarolitic cavities and voids of the ejecta, which consist mainly of sanidine and plagioclase (An ranging from 20 to 80%), with minor amounts of feldspathoid, clinopyroxene and/or clinoamphibole, magnetite, titanite, and zircon. Locally, accessory minerals include britholite-(Ce), baddeleyite, phosphate to silico-phosphate phases close in composition to the brabantite-cheralite series, thorite, fluorite, danburite, and vonsenite. The genesis of the new hellandite end-members can be related to late-stage post magmatic hydrothermal fluids enriched in Zr, Ti, REEs, and actinide elements.