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The present work reports the crystal-chemical characterization of micas from the Monte Arsiccio and Buca della Vena mines (Apuan Alps, Italy) through electron microprobe analysis, single-crystal X-ray diffraction, and Raman spectroscopy. The sample from the Monte Arsiccio mine can be classified as an intermediate member of the yangzhumingite-fluorophlogopite series, with average crystal-chemical formula (K0.85Na0.01Ba0.09)Σ=0.95(Mg2.11Fe2+0.23Fe3+0.11Cr3+0.01Al0.20Ti0.04☐0.30)Σ=3.00(Si3.20Al0.80)Σ=4.00O10.00F1.90Cl0.02(OH)0.08. Unit-cell parameters are a ~ 5.30, b ~ 9.18, c ~ 10.14 Å, β ~ 100.12°, V ~ 486.22 Å3, corresponding to the 1M polytype. Structure refinements, performed in C2/m space group, converged to R1 = 3.54 and 4.46% and provided Mg plus Fe occupancy in the range 86–94% for the octahedral M1 and M2 sites. Raman spectroscopy shows very weak bands in the OH stretching region at ~ 3690 and 3580 cm−1. The sample from the Buca della Vena mine has been identified as an (OH)-rich fluorophlogopite, with average crystal-chemical formula (K0.84Na0.02Ca0.01)Σ=0.87(Mg2.12Fe2+0.55Fe3+0.10Al0.18☐0.05)Σ=3.00(Si2.99Al1.01)Σ=4.00O10.00F1.02Cl0.09(OH)0.89. Its unit-cell parameters are a ~ 5.33, b ~ 9.22, c ~ 10.23 Å, β ~ 100.09°, V ~ 494.39 Å3. Structure refinements gave good R1 values (3.27 and 4.37%) and revealed octahedral occupancy of 82–84% Mg and 16–18% Fe. Strong Raman signals at ~ 3702 cm−1 and 3595 cm−1 were observed in the OH stretching region. The findings allow to better understand not only the mineralogy of the Apuan Alps but, more generally, the crystal chemical details of intermediate dioctahedral-trioctahedral mica belonging to the yanzhumingite-fluorophlogopite series. [ABSTRACT FROM AUTHOR]

The crystal structure of ferrinatrite, Na3[Fe(SO4)3]·3H2O, was refined based on a new single-crystal X-ray diffraction experiment on a sample from the type locality Sierra Gorda, Chile. The data allowed H to be successfully located and the H-bonding system to be defined. Infrared and Raman spectra are presented and discussed for this compound on the basis of the crystal structure. The Oacceptor···H-Odonor bond distances determined from the structure refinement agree well with the geometric correlation obtained from spectroscopic data. The thermal stability and dehydration process of ferrinatrite was investigated by in situ high temperature (HT) synchrotron X-ray powder diffraction, Raman and Fourier transform infrared spectroscopies. [ABSTRACT FROM AUTHOR]

The thermal dehydration process of fibroferrite, FeOH(SO)·5HO, 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(SO)·4HO, appearing at about 80 °C due to release of one interstitial HO 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. [ABSTRACT FROM AUTHOR]

The structure, structural disorder and chemistry of miserite from the charoite-bearing rocks of the Murun massif (Russia) and from alkaline-syenite pegmatitic rocks of the Dara-i-Pioz massif (Tajikistan) were investigated employing a combination of electron microprobe, single crystal diffraction and micro-Fourier transform infrared spectroscopy analysis. Chemical analysis of the sample investigated by X-ray diffraction evidenced that Dara-i-Pioz miserite has a greater REE concentration than Murun miserite (~0.22 vs. 0.05 apfu, respectively) and also contains Y (0.14 apfu), which is absent in Murun miserite. The occurrence of a band at about 1,600 cm testified to the presence of HO in miserite at hand. Structural analyses yielded average cell parameters of a = 10.092, b = 16.016, c = 7.356 Å, α = 96.60°, β = 111.27° and γ = 76.34°. Anisotropic structural refinement in space group P $$\bar{1}$$ converged at similar values for the analyzed samples ( R ~3.4, R ~3.8 %). An interesting feature shown by both the miserite specimen is the presence, revealed by difference Fourier analysis, of a disordered part of the structure. This turned out to be due to the flipping of the tetrahedra belonging to the isolated [SiO] diorthogroups, one of the two radicals (the other is [SiO]) characterizing the miserite structure. The sixfold and seven-vertex Ca polyhedra linked to the inverted diorthogroups show variation in coordination number with respect to those of the ordered structure. [ABSTRACT FROM AUTHOR]

In the present work, crystal chemical variations between 1 M and 2 M phlogopites coexisting in the same rock sample from kamafugite of Kasenyi (southwest Uganda, west branch of the East African Rift) were explored by electron probe microanalyses, single crystal X-ray diffraction and Mössbauer spectroscopy. Chemical analyses revealed close similarity both within and between the two polytypic arrangements as well as high TiO (~4.9 wt%) and AlO (~12.9 wt%), and low CrO (~0.8 wt%), F (~0.3 wt%) and BaO (~0.2 wt%) contents. Room temperature Fe Mössbauer investigation proved that the studied mica is a tetraferriphlogopite with: Fe = 19(1) %, Fe = 58(1) %, Fe = 23(1) %. Single crystal refinement showed that both polytypes have narrow range of variation in terms of some relevant unit cell parameters and similar values in terms of mean bond lengths, mean atomic numbers and distortion parameters. Similar substitutions were active in the structure of the 1 M and 2 M studied phlogopites. However, in 2 M polytypes the oxy-type substitutions were found to occur to a greater extent. Comparison of unit layer of 1 M mica (in the 2 M setting) with that of the 2 M ones showed that the 2 M polytypes are affected to different extent by relative shifts of the upper and lower triads of octahedral oxygens along the ± b directions. This effect did not cause any symmetry lowering in the T-O-T layer of the studied samples. [ABSTRACT FROM AUTHOR]

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This study presents a cross-correlated surface and near surface investigation of two phlogopite polytypes from Kasenyi kamafugitic rocks (SW Uganda) by means of advanced Atomic Force Microscopy (AFM), confocal microscopy and Raman micro-spectroscopy. AFM revealed comparable nanomorphology and electrostatic surface potential for the two mica polytypes. A widespread presence of nano-protrusions located on the mica flake surface was also observed, with an aspect ratio (maximum height/maximum width) from 0.01 to 0.09. Confocal microscopy showed these features to range from few nm to several μm in dimension, and shapes from perfectly circular to ellipsoidic and strongly elongated. Raman spectra collected across the bubbles showed an intense and convolute absorption in the range 3000-2800 cm−1, associated with weaker bands at 1655, 1438 and 1297 cm−1, indicating the presence of fluid inclusions consisting of aliphatic hydrocarbons, alkanes and cycloalkanes, with minor amounts of oxygenated compounds, such as carboxylic acids. High-resolution Raman images provided evidence that these hydrocarbons are confined within the bubbles. This work represents the first direct evidence that phlogopite, a common rock-forming mineral, may be a possible reservoir for hydrocarbons. [ABSTRACT FROM AUTHOR]