Maria Lacalamita

XRD, micro-XANES, EMPA, and SIMS investigation on phlogopite single crystals from Mt. Vulture (Italy)

Abstract Selected phlogopite flakes from Mt. Vulture in southern Italy were studied using a combination of single-crystal techniques: electron microprobe analysis (EMPA), secondary ion mass spectrometry (SIMS), single-crystal X-ray diffraction (SCXRD), and micro-X-ray absorption near-edge spectroscopy (XANES). The latter technique was employed to analyze the structure of the Fe-K absorption edge over the region from 7080-8100 eV and to determine Fe3+/∑Fe at a micrometer scale, albeit with large error bars due to known effects of orientation on pre-edge energy. The annite component, Fe/(Mg-i-Fe), of the samples studied ranged from 0.16 to 0.31, the Ti content from 0.11 to 0.27 atoms per formula unit (apfii) and the Ba content from 0.03 to 0.09 apfu. SIMS analysis showed H2O (wt%) = 1.81-3.30, F (wt%) = 0.44-1.29, and Li2O (wt%) = 0.001-0.027. The intra single-crystal chemical variability for major/minor elements (Mg, Fe, Al, Ba, Ti, and K) was found particularly significant for samples VUT191_11 and PG5_1, less significant for the other samples of the set. SIMS data relative to crystals VUT187_24, VUT191_10, VUT191_11, and VUT187_28 showed a noteworthy variation in the concentrations of some light elements (H, Li, and F) with coefficient of variation CV (as 1σ%) up to -18% for H2O. The analyzed micas belong to the 1M polytype. Structure refinements using anisotropic displacement parameters were performed in space group Clim and converged at 3.08 <R < 3.63,3.32 <RW < 3.98%. Micro-XANES results yielded Fe3+/£Fe from 51-93%. Previous Mossbauer data from powdered samples suggested Fe3+/∑Fe values ranging from 49-87%. However, the Fe3+ content determined by both techniques is sometimes remarkably different, in part because of the large errors (±10-15%) presently associated with the micro-XANES technique and m part because the Fe3+ content of a single crystal may significantly depart from the average value obtamed from routine Mossbauer analysis. The combination of EMPA, SIMS, and micro-XANES resulted in the characterization of the samples at a comparable spatial scale. By means of in-situ data and the results of crystallographic investigations, the occurrence of different relative amounts of M3*-oxy [VIM2+ + (OH)- ↔ VIM3+ + O2- + ½H2↑], Ti-oxy substitutions [VIM2+ + 2(OH)- ↔VITi4+ + 2O2- + H2↑], and Ti-vacancy (⃞) substitution (2VIM2+ ↔ + VITi4+ + VI⃞) was ascertained for the studied samples.

Substitution mechanisms and implications for the estimate of water fugacity for Ti-rich phlogopite from Mt. Vulture, Potenza, Italy

Abstract The crystal chemistry of Ti-rich phlogopite from deposits of the oldest activity (~740 ka) of Mt. Vulture, Potenza, Italy, was investigated to identify the substitution mechanisms in Ti-rich phlogopite and to determine its potential as a geohygrometer. Substitution mechanisms were determined by electron probe microanalysis (EPMA), single-crystal X‑ray diffraction (SCXRD), Mössbauer spectroscopy, and micro-Fourier transform infrared (FTIR) spectroscopy. Magnetite and sanidine from the mica-rich host rocks were also analyzed. Use of the biotite-magnetite-sanidine geohygrometer in these volcanics (essentially trachytic-phonolitic ignimbrites) is exploited. All investigated phlogopite samples consist of the 1M polytype, with 5.3275(2) ≤ a ≤ 5.3635(4) Å, 9.2211(4) ≤ b ≤ 9.2958(8) Å, 10.1211(5) ≤ c ≤ 10.281(1) Å, and 99.980(3) ≤ β ≤ 100.097(2)°. Structure refinements in space group C2/m converged to 2.42 ≤ R1 ≤ 4.00% and 2.04 ≤ wR2 ≤ 4.50%. VIFe3+/Fetot from Mössbauer analyses ranged from 34(1)-89(1)%. The main bands in the OH-stretching region are 3709, 3682, and 3658 cm-1, and were assigned to 3Mg-OH--K-OH-, 3Mg-OH--K-O2-, and 2MgFe3+- OH--K-O2- local configurations, respectively. The overall crystal chemical features are compatible with the M3+ -Tschermak substitutions (VIM2+ + IVSi4+ ↔ VIM3+ + IVAl, with M3+ = Al,Fe3+), M3+-oxy [VIM2+ + (OH)- ↔ M3+ + (O)2- + ½H2↑] and Ti-oxy substitutions [VIM2+ + 2(OH)- → VITi4+ + 2(O)2- + H2↑]. The magnetite composition varies between Mt82Uv18 and Mt93Uv07, whereas the proportion of orthoclase with respect to albite plus anorthite is 0.77 ≤ XOr ≤ 0.82. A partly ionic model was used to estimate annite activity, starting from experimentally determined substitutions in phlogopite. The resulting water fugacity was an order of magnitude lower than that calculated using stoichiometry to determine the phlogopite formula. The results are consistent with the occurrence of a well-developed hydrothermal system that altered the magmatic oxygen fugacity conditions at Mt. Vulture.

Crystal chemistry of trioctahedral micas-2M1 from Bunyaruguru kamafugite (southwest Uganda)

Abstract The crystal chemistry of 2M1 micas from Bunyaruguru kamafugite (southwest Uganda) was studied by electron probe microanalysis, single-crystal X-ray diffraction, Mössbauer and Fourier transform infrared spectroscopy. Chemical analyses showed that the studied crystals are Ti-rich, F-poor phlogopites with an annitic component, Fetot/(Fetot + Mg), ranging from 0.15 to 0.22. Unit-cell parameters from single-crystal X-ray data are in the range: 5.3252(1) ≤ a ≤ 5.3307(1), 9.2231(3) ≤ b ≤ 9.2315(3), 20.1550(6) ≤ c ≤ 20.1964(8) Å, and 94.994(2) ≤ β ≤ 95.131(2)°. Anisotropic structure refinements, in the space group C2/c, converged to 2.77 ≤ R1 ≤ 3.52% and 2.91 ≤ wR2 ≤ 4.02%. Mössbauer spectroscopy showed that the studied sample has: VIFe2+ = 60(1)%, VIFe3+ = 24(1)%, and IVFe3+ = 16(1)%. FTIR investigations pointed to the occurrence of Fe3+-oxy substitutions and ruled out the presence of vacancy mechanisms. The overall crystal-chemical features are consistent with the following substitutions: tetraferriphlogopite [IVFe3+ ≤ IVAl]; Ti-oxy [VIM2+ + 2 (OH)- ↔ VITi4+ + 2 (O2-) + H2↑] and Al, Fe3+, Cr-oxy [VIM2+ + (OH)- ↑VIM3+ + O2- + ½ (H2)↑]; Al, Fe3+-Tschermak [VIM2+ + IVSi4+ ↔ VIM3+ + IVAl]; kinoshitalite [XIIK + IVSi4+ ↔ XIIBa2+ + IVAl] and [XIIK+ + IVAl3+ ↔ IVSi4+ + XII⃞]. The estimation of the OH- content for Ugandan mica-2M1 was obtained, for the first time, from the linear regression equation c = 0.20(2) × OH- (gpfu) + 19.93(2) derived from literature data of 2M1-samples with known OH− content. The orientation of the O-H vector with respect to c* was found in the range from 2.0 to 6.9°.

Crystal chemistry of Ti-rich fluorophlogopite from Presidente Olegario, Alto Paranaíba igneous province, Brazil

Abstract Trioctahedral micas from kamafugitic lavas of Presidente Olegario (Brazil) are Ti-Fe-bearing fluorophlogopites. They were investigated using a combination of electron probe microanalysis (EPMA), single-crystal X-ray diffraction (SCXRD), and Mössbauer spectroscopy. EPMA data yielded the following ranges: Al2O3 (8.7-10.1 wt%), MgO (19.6-20.6 wt%), FeO (5.7-6.5 wt%), TiO2 (5.9-7.5 wt%), K2O (8.9-9.7 wt%), Na2O (0.4 -0.6 wt%), and fluorine (3.4-4.1 wt%). Mössbauer investigation indicated: VIFe2+ - 60%, VIFe3+ - 10%, IVFe3+ - 30%. X-ray analysis indicated the 1M polytype, with cell parameters in the range a = 5.3208-5.3376, b = 9.2210-9.2464, c = 10.1227-10.155 Å, β = 100.157-100.194°. Structure refinements using anisotropic displacement parameters were performed in space group C2/m and converged to 2.01 ≤ R1 ≤ 3.51, 2.00 ≤ wR2 ≤ 3.51%. The micas have no VIAl3+ and Na is probably partitioned over both interlayer and octahedral sites. Major substitutions are OH− ↔ F−, and the Ti-oxy substitution: VIM2+ + 2(OH)− ↔ VITi4+ + 2O2- + H2↑. Accordingly, the structural features of the studied micas encompass those typical of both fluorophlogopites and micas affected by Ti-oxy substitution.

Use of natural clays as sorbent materials for rare earth ions: Materials characterization and set up of the operative parameters

Two mineral clays of the montmorillonite group were tested as sorbents for the removal of Rare Earths (REs) from liquid solutions. Lanthanum and neodymium model solutions were used to perform uptake tests in order to: (a) verify the clays sorption capability, (b) investigate the sorption mechanisms and (c) optimize the experimental parameters, such as contact time and pH. The desorption was also studied, in order to evaluate the feasibility of REs recovery from waters. The adsorption-desorption procedure with the optimized parameters was also tested on a leaching solution obtained by dissolution of a dismantled NdFeB magnet of a hard-disk. The clays were fully characterized after REs adsorption and desorption by means of X-ray powder diffraction (XRPD) and X-ray photoelectron spectroscopy (XPS); the liquid phase was characterized via Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) analyses. The experimental results show that both clays are able to capture and release La and Nd ions, with an ion exchange mechanism. The best total efficiency (capture ≈ 50%, release ≈ 70%) is obtained when the uptake and release processes are performed at pH=5 and pH=1 respectively; in real leached scrap solutions, the uptake is around 40% but release efficiency is strongly decreased passing from a mono-ion system to a real system (from 80% to 5%). Furthermore, a strong matrix effect is found, with the matrix largely affecting both the uptake and the release of neodymium.

3T-phlogopite from Kasenyi kamafugite (SW Uganda): EPMA, XPS, FTIR, and SCXRD study

Abstract A 3T mica polytype from Kasenyi (southwest Uganda), kamafugite, was studied by electron probe microanalysis (EPMA), single-crystal X-ray diffraction (SCXRD), micro-Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) to characterize its crystal chemistry and the relationships with phlogopites from the same rock but showing different stacking sequence and to get insights into factors affecting polytypism in Ugandan phlogopites. EPMA data gave: SiO2 = 38.7(2), Al2O3 = 13.08(9), MgO = 20.4(2), TiO2 = 4.8(1), MnO = 0.03(3), FeOtot = 5.51(9), Cr2O3 = 0.90(7), NiO = 0.11(5), SrO = 0.03(3), ZnO = 0.04(3), ZrO2 = 0.01(2), K2O = 9.64(5), Na2O = 0.29(1), BaO = 0.15(5), F = 0.13(5), and Cl = 0.01(1) wt%. The analyzed sample may be classified as a Ti-rich phlogopite. X-ray photoelectron spectroscopy provided Fe3+/Fe2+ and O2-/OH equal to ~0.75 and 7.14, respectively, which are in agreement with the results of previous Mössbauer investigation on the BU1 phlogopites from the same rock and with the structural formula of the studied crystal. Infrared spectra showed a shoulder at ~3660 cm-1 in the OH− stretching region (~3740-3600 cm-1), which is assigned to MgMgFe3+-OH−-K-O2- local configurations. No evidences of vacancy substitutions were observed. Structure refinement based on single-crystal X-ray diffraction data was performed in space group P3112 using anisotropic displacement parameters and converged to R1 = 4.34 and wR2 = 3.33%. Unitcell parameters are: a = b = 5.3235(3) and c = 30.188(2) Å. Geometrical and chemical considerations point to a disordered cation distribution over T1 and T2 tetrahedral sites, whereas partial cation ordering characterizes the octahedral sites with high-charge cations preferentially located as expected on M2 and M3. Tetrahedral bond length distortion and angular variance parameters describe more distorted polyhedra in 3T polytype than those found in coexisting 1M and 2M1 polytypes. Finally, the overall crystal-chemical features indicate the occurrence of the following substitution mechanisms in the studied sample: Ti-oxy [VIM2++2(OH)- ↔ VITi4++2(O2-)+H2↑] and Al, Fe3+, Croxy [VIM2++(OH)- ↔ VIM3++O2-+½(H2)↑]; Al, Fe3+-Tschermak [VIM2++IVSi4+ ↔ VI(Al3+, Fe3+)+IVAl3+]; XIIK++IVAl3+ ↔ IVSi4++XII⃞; tetraferriphlogopite [IVFe3+↔ IVAl].

Crystal chemistry and light elements analysis of Ti-rich garnets

Abstract A suite of Ti-bearing garnets from magmatic, carbonatitic, and metamorphic rocks was studied by electron probe microanalysis (EPMA), X-ray powder diffraction (XRPD), single-crystal X-ray diffraction (SCXRD), Mössbauer spectroscopy, and secondary ion mass spectrometry (SIMS) to better characterize their crystal chemistry. The studied garnets show TiO2 varying in the range of 4.9(1) to 17.1(2) wt% and variable Fe3+/ΣFe content. SIMS analyses allowed quantification of light elements yielding H2O in the range 0.091(7)–0.46(4), F in the range 0.004(1)–0.040(4), and Li2O in the range 0.0038(2)–0.014(2) wt%. Mössbauer analysis provided spectra with different complexity, which could be fitted to several components variable from one (YFe3+) to four (YFe2+, ZFe2+, YFe3+, ZFe3+). A good correlation was found between the Fe3+/ΣFe resulting from the Mössbauer analysis and that derived from the Flank method. X-ray powder analysis revealed that the studied samples are a mixture of different garnet phases with very close cubic unit-cell parameters as recently found by other authors. Single-crystal X-ray refinement using anisotropic displacement parameters were performed in the Ia3d space group and converged to 1.65 ≤ R1 ≤ 2.09% and 2.35 ≤ wR2 ≤ 3.02%. Unit-cell parameters vary in the range 12.0641(1) ≤ a ≤ 12.1447(1) Å, reflecting different Ti contents and extent of substitutions at tetrahedral site. The main substitution mechanisms affecting the studied garnets are: YR4+ + ZR3+ ↔ ZSi + YR3+ (schorlomite substitution); YR2+ + ZR4+ ↔ 2YR3+ (morimotoite substitution); YR3+ ↔ YFe3+ (andradite substitution); in the above substitutions YR2+ = Fe2+, Mg2+, Mn2+; ZR4+ = Ti; YR3+ = Fe3+, Al3+, Cr3+;ZR3+ = Fe3+, Al3+. Minor substitutions, such as 2YTi4++ ZFe2+ ↔ 2YFe3+ + ZSi, (SiO4)4– ↔ (O4H4)4–, F– ↔ OH–, and YR4+ + XR+ ↔ YR3+ + XCa2+, with YR4+ = Ti, Zr; YR3+ = Fe3+, Al, Cr3+; XR+ = Na, Li also occur.

Tobelite and NH4 -rich muscovite single crystals from Ordovician Armorican sandstones (Brittany, France): Structure and crystal chemistry

Abstract The crystal structures of tobelite and NH+4-rich muscovite from the sedimentary rocks of the Armorican sandstones (Brittany, France) have been solved for the first time by single-crystal X-ray diffraction. The structural study was integrated by electron probe microanalyses, and X-ray photoelectron and micro-Fourier transform infrared spectroscopy. The crystals belong to the 2M2 polytype with the following unit-cell parameters: a = 9.024(1), b = 5.2055(6), c = 20.825(3) Å, and â = 99.995(8)° for tobelite and a = 9.027(1), b = 5.1999(5), c = 20.616(3) Å, and β = 100.113(8)° for NH+4-rich muscovite. Structure refinements in the space group C2/c converged at R1 = 8.01%, wR2 = 8.84% and R1 = 5.59%, wR2 = 5.63% for tobelite and NH+4-rich muscovite, respectively. X-ray photoelectron spectroscopy revealed nitrogen environments associated either with inorganic (B.E. 401.31 eV) or organic (B.E. 398.67 eV) compounds. Infrared spectra showed, in the OH-- stretching region (3700-3575 cm-1), two prominent bands, centered at ~3629 and ~3646 cm-1, and two shoulders at ~3664 and ~3615 cm-1 that were assigned to Al3+Al3+□-OH- arrangements having OH- groups affected by different local configurations. In addition, a series of overlapping bands from about 3500 to 2700 cm-1 characteristic of the NH+4-stretching vibrations, a main band at ~1430 and a shoulder at ~1460 cm-1 that were associated to the NH+4-bending vibration (ν4) were also present. The ammonium concentration was semi-quantitatively estimated in both crystals from the absorbance of the OH--stretching and NH+4-bending vibrations in the infrared spectra. An additional estimate was obtained for the NH+4-rich muscovite by considering the normalized peak area between K2p3/2 and N1s in the X-ray photoelectron spectrum. The obtained values are in agreement with those derived from the interlayer spacing in the simulated X-ray powder diffraction spectra. The results of this integrated approach converged to (K0.18Na0.01NH+4 0.62)∑=0.81(Al1.98Fe2+0.02)∑=2.00 (Si3.19Al0.81)∑=4.00O10.00OH2.00 for tobelite and to (K0.46Na0.03Ba0.01NH+40.36)∑=0.86(Al1.98Mg0.01Fe2+0.01V3+0.01)∑=2.01 (Si3.13Al0.87)∑=4.00O10.00F0.08OH1.92 for NH+4-rich muscovite.

Kinetics of Fe-oxidation/deprotonation process in Fe-rich phlogopite under isothermal conditions

Abstract The kinetics of the Fe-oxidation/deprotonation process in a natural Fe-rich phlogopite from Mt. Vulture (Potenza, Italy) was studied under isothermal conditions by in situ high-temperature singlecrystal X-ray diffraction. Isothermal annealing experiments were performed at five temperatures in the range 640-750 °C on five crystals with similar chemical composition and lattice parameters. The Fe-oxidation/deprotonation process at high temperature occurs with a reduction of unit-cell parameters and cell volume. The changes in unit-cell parameters measured at high temperature and during cooling show that the same degree of Fe-oxidation/deprotonation process was achieved at all temperatures. Changes in unit-cell parameters with temperature and time show that the kinetics of Fe-oxidation/ deprotonation in phlogopite follows an exponential law, and the temperature dependence follows the Arrhenius relation. A kinetic analysis was performed and good agreement was obtained with the onedimensional diffusion model. An apparent activation energy of 195(4) kJ/mol was determined.

Armstrongite from Khan Bogdo (Mongolia): Crystal structure determination and implications for zeolite-like cation exchange properties

Abstract The results of a combined electron probe microanalysis, single-crystal X-ray diffraction, and Fourier transform infrared study of a crystal of armstrongite from Khan Bogdo deposit (Gobi, Mongolia) are reported. Major element analysis provided (wt%): CaO 9.2(1), ZrO2 20.9(2), and SiO2 62.5(2). Significant concentrations of REE (0.45 wt%) were also detected. From single-crystal structural refinement, armstrongite resulted monoclinic [space group C2/m, a = 14.0178(7), b = 14.1289(6), c = 7.8366(3) Å, b = 109.436(3)°, V = 1463.6(1) Å3, Z = 4] and twinned with two individuals rotated around a twin twofold axis parallel to [100]. The analyzed crystal was refined up to R = 3.3% (Rw = 2.9%). The structural refinement showed that the investigated armstrongite has only two water groups per formula unit consistent with the infrared analysis. Indeed, the occurrence in the infrared spectrum of the armstrongite (here reported for the first time) of two bending vibration bands at about 1640 and 1610 cm-1 testifies to the presence of two water groups environments. The results of this integrated approach converged to the following empirical formula (based on Si = 6 atoms per formula unit): (Ca0.96Ce0.01Yb0.01)Zr0.99Si6O14.97·2.02H2O. Finally, the studied mineral shows a framework density (FD = 21.86) lying in the range of zeolites and microporous heterosilicates with tetrahedral-octahedral frameworks. The determined crystal chemical features are relevant for the possible employment of this mineral or of its synthetic analogs for technological applications.