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This work reports the synthesis and crystal-chemistry of ferri-clinoferroholmquistite in the system Li(2)O - FeO - Fe(2)O(3) - SiO(2) - H(2)O. Ferri-clinoferroholmquistite has a very restricted temperature stability. An almost monophase amphibole product is obtained at 500degreesC for a wide pressure range (1-7 kbar), whereas a Li-bearing pyroxene becomes predominant for T greater than or equal to 600degreesC. The X-ray powder pattern of ferri-clinoferroholmquistite was indexed in the C2/m space group. Refined cell dimensions are: a = 9.489 (2), b = 18.036 (7), c = 5.313 (3) Angstrom; beta = 101.59 (3). Infrared spectra in the OH-stretching region show the presence of a single and very sharp band at 3614 cm(-1), which is assigned to the Fe(2+)Fe(2+)Fe(2+) trimer at the OH-coordinated M1M1M3 octahedra, and a small satellite band at 3644 cm(-1) which was assigned to Li at M3. Mossbauer spectra can be fitted to three doublets assigned to Fe(3+) at M2, Fe(2+) at M1 and Fe(2+) at M3, respectively, with a calculated Fe(2+)/Fe(2+) ratio of 2/3, suggesting a composition close to the nominal one. The spectroscopic data show that synthetic ferri-clinoferroholmquistite has a strongly ordered cation distribution, in agreement with single-crystal refinements done by Caballero et al. (1998) and Oberti et al. (2000) on natural samples with related Li-rich compositions.

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.

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.

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.

This paper presents the results of a combined electron microprobe and analytical TEM study that describes the chemical and structural characteristics of non-metamict zirconolite from a volcanic ejectum collected within a pyroclastic formation of the Vico volcanic complex, near Tre Croci Community, Latium (Italy). The host rock is a foid-bearing alkali-syenite and consists of potassium-feldspar and plagioclase, with minor biotite, titanite, clinopyroxene and magnetite. Sodalite occurs as well-faceted crystals inside miarolitic cavities between intersecting feldspars and it is variably altered to a kaolinite-like product. Accessory minerals include zircon, baddeleyite, stillwellite, hellandite, fluorite, apatite and monazite. Zirconolite occurs both as elongated acicular crystals of orthorhombic symmetry (zirconolite-3 O ), space group Acam, with (in A) a = 10.13(1), b = 14.16(1) and c = 7.288(2), and as pseudo-hexagonal platy crystals of trigonal symmetry (zirconolite-3 T ), space group P 3 1 2, with a = 7.279(2) and c = 16.89(2). TEM studies revealed additionally the presence of polytype zirconolite-2 M in a subset of grains analyzed. Zirconolite displays pronounced compositional zoning, observed in backscattered electron images, resulting mainly from an antipathetic variation in the actinide elements (Th + U) and REE contents. Analytical TEM results indicate compositional differences exist between the zirconolite-3 T and zirconolite-2 M polytypes. Zirconolite, and associated accessory REE, Th, U minerals crystallized after the formation of the major rock-forming minerals of the ejectum, from metasomatic fluids rich in F and P.