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1.
Babingtonite, Ca2Fe2+Fe3+[Si5O14(OH)] (Z?=?2, space group $ P\overline{1} $ ) from Yakuki mine (Japan), Grönsjöberget (Sweden), Kandivali Quarry (India), Baveno Quarry (Italy), Bråstad Mine (Norway), and Kouragahana (Japan), and manganbabingtonite, Ca2(Mn2+, Fe2+)Fe3+[Si5O14(OH)], from Iron Cap mine (USA) were studied using electron-microprobe analysis (EMPA), 57Fe Mössbauer analysis and single-crystal X-ray diffraction methods to determine the cation distribution at M1 and M2 and to analyze its effect on the crystal structure of babingtonite. Although all studied babingtonite crystals are relatively homogeneous, chemical zonation due to mainly Fe ? Mn substitution is observed in manganbabingtonite. Mössbauer spectra consist of two doublets with isomer shift (I.S.)?=?1.16–1.22 mm/s and quadrupole splitting (Q.S.)?=?2.33–2.50 mm/s and with I.S.?=?0.38–0.42 mm/s and Q.S.?=?0.82–0.90 mm/s, assigned to Fe2+ and Fe3+ at the M1 and M2 octahedral sites, respectively. The determined ratio of Fe2+/total Fe in manganbabingtonite (0.26) was smaller than that in the others (0.35–0.44) because of high Mn2+ content instead of Fe2+. The unit-cell parameters of babingtonite are a?=?7.466–7.478, b?=?11.624–11.642, c?=?6.681–6.690 Å, α?=?91.53–91.59, β?=?93.86–93.94, γ?=?104.20–104.34º, and V?=?560.2–562.3 Å3, and those of manganbabingtonite are a?=?7.4967(3), b?=?11.6632(4), c?=?6.7014(2) Å, α?=?91.602(2), β?=?93.989(2), γ?=?104.574(3)º, and V =565.09(5) Å3. Structural refinements converged to R 1 values of 1.64–3.16 %. The <M1-O> distance was lengthened due to the substitution of large octahedral cations such as Mn2+ for Fe2+. The increase of the M1-O8, M1-O8’ and M1-O13 lengths with mean ionic radii is slightly more pronounced than of the other M1-Oi lengths. The lengthened M1-O13 distance leads the positive correlation between Si5-O15-Si1 angle and M1-O13 distance. The increase of Si2-O3-Si1 and Si5-O12-Si4 angles due to the increase of mean ionic radius of M2 is also observed. 相似文献
2.
Sergey V. Krivovichev Stanislav K. Filatov Lidiya P. Vergasova 《Mineralogy and Petrology》2013,107(2):235-242
The crystal structure of ilinskite, NaCu5O2(SeO3)2Cl3, a rare copper selenite chloride from volcanic fumaroles of the Great fissure Tolbachik eruption (Kamchatka peninsula, Russia), has been solved by direct methods and refined to R 1?=?0.044 on the basis of 2720 unique observed reflections. The mineral is orthorhombic, Pnma, a?=?17.769(7), b?=?6.448(3), c?=?10.522(4) Å, V?=?1205.6(8) Å3, Z?=?4. The The CuOmCln coordination polyhedra share edges to form tetramers that have 'additional' O1 and O2 atoms as centers. The O1Cu4 and O2Cu4 tetrahedra share common Cu atoms to form [O2Cu5]6+ sheets. The SeO3 groups and Cl atoms are adjacent to the [O2Cu5]6+ sheets to form complex layers parallel to (100). The Na+ cations are located in between the layers. A review of mixed-ligand CuOmCln coordination polyhedra in minerals and inorganic compounds is given. There are in total 26 stereochemically different mixed-ligand Cu-O-Cl coordinations. 相似文献
3.
Optical absorption spectra (OAS) of synthetic single crystals of the solid solution spinel sensu stricto (s.s.)–magnesioferrite, Mg(Fe3+Al1???y)2O4 (0?y?≤ 0.3), have been measured between 12 500 and 28 500?cm?1. Chemical composition and Fe3+ site distribution have been measured by electron microprobe and Mössbauer spectroscopy, respectively. Ferric iron is ordered to the tetrahedral site for samples with small magnesioferrite component, and this ordering is shown to increase with magnesioferrite component. The optical absorption spectra show a strong increase in band intensities with Fe3+→Al substitution. Prominent and relatively sharp absorption bands are observed at 25 300 and 21 300?cm?1, while less intense bands occur at 22 350, 18 900, 17 900 and 15 100?cm?1. On the basis of band energies, band intensities and the compositional effect on band intensity, as well as structural considerations, we assign the observed bands to electronic transitions in IVFe3+–VIFe3+clusters. A linear relationship (R 2= 0.99) between the αnet value of the absorption band at 21 300?cm?1 and [IVFe3+]?·?[VIFe3+] concentration product has been defined: αnet=2.2?+?15.8 [IVFe3+]?·?[VIFe3+]. Some of the samples have been heat-treated between 700 and 1000?°C to investigate the relation between Fe3+ ordering and absorption spectra. Increase of cation disorder with temperature is observed, which corresponds to a 4% reduction in the number of active clusters. Due to the high spatial resolution (??~?10?μm), the OAS technique may be used as a microprobe for determination of Fe3+ concentration or site partitioning. Potential applications of the technique include analysis of small crystals and of samples showing zonation with respect to total Fe3+ and/or ordering. 相似文献
4.
S. Nazzareni P. Comodi L. Bindi G. Garbarino A. Bobrov 《Physics and Chemistry of Minerals》2012,39(7):553-559
We investigated the high-pressure behaviour of Fe3+-bearing hydrous phase-X, (K1.307Na0.015)(Mg1.504Fe 0.373 3+ Al0.053Ti 0.004 4+ )Si2O7H0.36, up to 34?GPa at room temperature by synchrotron X-ray powder diffraction. The lattice parameters behave anisotropically, with the [001] direction stiffer than [100]. In the 10?4 to 22?GPa pressure range, the axial bulk moduli are K 0a ?=?112(3) GPa and K′?=?4, and K 0c ?=?158(2) GPa and K′?=?4, and the anisotropy of the lattice parameters is β0c :β0a ?=?0.71:1. The cell volumes are fitted by a second-order Birch–Murnaghan equation of state giving a bulk modulus of K 0?=?127(1) GPa and K′?=?4 in the same pressure range. After 22?GPa, a discontinuity in volume and lattice parameters can be recognized. Sample did not become amorphous up to 34?GPa. The coupled substitution K?+?Mg?=?[]?+?Fe3+ has only a limited influence on the bulk modulus and structural stability of phase-X. 相似文献
5.
Plumboselite, ideally Pb3O2(SeO3), is a new selenite (IMA2010?C028) from the Tsumeb mine, Namibia. It occurs as fibres on clausthalite and is also associated with smithsonite, mimetite and vaterite. Plumboselite occurs in subparallel to divergent clusters of thin, flattened, colourless fibres up to 0.3?mm in length, but not exceeding 5???m in width and 2???m in thickness. The fibres are elongated parallel to [001] and flattened on {010}, with {010} the only form observed. The crystals have a dull to adamantine lustre and a white streak. The tenacity is brittle and the Mohs hardness is estimated to be between 2 and 3. Plumboselite crystals are optically biaxial with parallel extinction and are length fast in all orientations. The Gladstone-Dale relationship predicts n av?=?2.115. The high indices of refraction and small crystal size prevented the determination of other optical properties. The calculated density is 7.814?g/cm3. The empirical formula (based on 5 O atoms) is Pb2.92Ca0.01Se1.03O5. Plumboselite is orthorhombic, space group Cmc21, a?=?10.5384(11), b?=?10.7452(13), c?=?5.7577(7) ?, V?=?651.98(12) ?3 and Z?=?4. The five strongest lines in the powder X-ray diffraction pattern are [d obs in ?/(I)/hkl]: 3.155/(100)/221; 1.956/(26)/042,402; 2.886/(22)/311,002; 1.713/(21)/223; 2.691/(17)/040. The crystal structure was solved from single-crystal X-ray diffraction data and refined to R 1?=?0.0371 on the basis of 200 unique reflections with F o?>?4??F. The structure is based on double [O2Pb3] chains of edge-sharing oxo-centered [OPb4] tetrahedra along c, between which are sited SeO3 triangles. The two independent Pb2+ atoms and the Se4+ atom have sterochemically active lone electron pairs. 相似文献
6.
Fernando Cámara Gianluca Iezzi Massimo Tiepolo Roberta Oberti 《Physics and Chemistry of Minerals》2006,33(7):475-483
Lithian ferrian enstatite with Li2O = 1.39 wt% and Fe2O3 7.54 wt% was synthesised in the (MgO–Li2O–FeO–SiO2–H2O) system at P = 0.3 GPa, T = 1,000°C, fO2 = +2 Pbca, and a = 18.2113(7), b = 8.8172(3), c = 5.2050(2) Å, V = 835.79(9) Å3. The composition of the orthopyroxene was determined combining EMP, LA-ICP-MS and single-crystal XRD analysis, yielding the unit formula M2(Mg0.59Fe 0.21 2+ Li0.20) M1(Mg0.74Fe 0.20 3+ Fe 0.06 2+ ) Si2O6. Structure refinements done on crystals obtained from synthesis runs with variable Mg-content show that the orthopyroxene is virtually constant in composition and hence in structure, whereas coexisting clinopyroxenes occurring both as individual grains or thin rims around the orthopyroxene crystals have variable amounts of Li, Fe3+ and Mg contents. Structure refinement shows that Li is ordered at the M2 site and Fe3+ is ordered at the M1 site of the orthopyroxene, whereas Mg (and Fe2+) distributes over both octahedral sites. The main geometrical variations observed for Li-rich samples are actually due to the presence of Fe3+, which affects significantly the geometry of the M1 site; changes in the geometry of the M2 site due to the lower coordination of Li are likely to affect both the degree and the kinetics of the non-convergent Fe2+-Mg ordering process in octahedral sites. 相似文献
7.
Six natural chloritoid crystals with Fe2+ and Fe3+ contents ranging from 4.15 to 12.81 and from 0.411 to 0.849g-atoms/l, respectively, as determined by means of microprobe and Mössbauer techniques, served as reference material to develop non-destructive microscope-spectrophotometric methods for quantitative Fe2+ – Fe3+ determinations in chloritoids from unpolarized spectra of (001) platelets. Fe2+ concentrations in g-atom/l can be obtained from [ [Fe3+]=C1xD1/t where D1 = log10(I0/I at 28,000 cm-1 and t=crystal thickness in cm; C1 is a conttant that may be influenced somewhat by experimental conditions and is found to be 0.002289 with the experimental set-up used in this study. Fe2+ concentrations in g-atom/l can be obtained from [Fe2+]=C1xD1/D1-C3 with D2=log10(I0/I) at 16,300 cm?1 and constants C4 = 45.36 and C5 = 3.540. Due to the uncertainties in absorbance measurements, D1 and D2 and the thickness measurements, the accuracies are ±0.05 and ±0.15 g-atom/l for [Fe3+] and [Fe2+], respectively. The determinations may be carried out on chloritoid grains in normal thin sections with an areal resolution of ~10 μm. 相似文献
8.
G. J. Redhammer G. Tippelt G. Roth W. Lottermoser G. Amthauer 《Physics and Chemistry of Minerals》2000,27(6):419-429
Natural barbosalite Fe2+Fe3+ 2 (PO4)2(OH)2 from Bull Moose Mine, South Dakota, U.S.A., having ideal composition, was investigated with single crystal X-ray diffraction techniques, Mössbauer spectroscopy and SQUID magnetometry to redetermine crystal structure, valence state of iron and evolution of 57Fe Mössbauer parameter and to propose the magnetic structure at low temperatures. At 298?K the title compound is monoclinic, space group P21/n, a o ?= 7.3294(16)?Å, b o ?=?7.4921(17)?Å, c o ?=?7.4148 (18)?Å, β?=?118.43(3)°, Z?=?2. No crystallographic phase transition was observed between 298?K and 110?K. Slight discontinuities in the temperature dependence of lattice parameters and bond angles in the range between 150?K and 180?K are ascribed to the magnetic phase transition of the title compound. At 298?K the Mössbauer spectrum of the barbosalite shows two paramagnetic components, typical for Fe2+ and Fe3+ in octahedral coordination; the area ratio Fe3+/Fe2+ is exactly two, corresponding to the ideal value. Both the Fe2+ and the Fe3+ sublattice order magnetically below 173?K and exhibit a fully developed magnetic pattern at 160?K. The electric field gradient at the Fe2+ site is distorted from axial symmetry with the direction of the magnetic field nearly perpendicular to Vzz, the main component of the electric field gradient. The temperature dependent magnetic susceptibility exhibits strong antiferromagnetic ordering within the corner-sharing Fe3+-chains parallel to [101], whereas ferromagnetic coupling is assumed within the face-sharing [1?1?0] and [?1?1?0] Fe3+-Fe2+-Fe3+ trimer, connecting the Fe3+-chains to each other. 相似文献
9.
Andreas Ertl Heinrich Mali Ralf Schuster Wilfried Körner John M. Hughes Franz Brandstätter Ekkehart Tillmanns 《Mineralogy and Petrology》2010,99(1-2):89-104
Pale-blue to pale-green tourmalines from the contact zone of Permian pegmatites to mica schists and marbles from different localities of the Austroalpine basement units (Rappold Complex) in Styria, Austria, are characterized. All these Mg-rich tourmalines have small but significant Li contents, up to 0.29 wt% Li2O, and can be characterized as dravite, with FeO contents of ?~?0.9–2.7 wt%. Their chemical composition varies from X (Na0.67Ca0.19?K0.02?0.12) Y (Mg1.26Al0.97Fe2+ 0.36Li0.19Ti4+ 0.06Zn0.01?0.15) Z (Al5.31?Mg0.69) (BO3)3 Si6O18 V (OH)3? W [F0.66(OH)0.34], with a?=?15.9220(3), c?=?7.1732(2) Å to X (Na0.67Ca0.24?K0.02?0.07) Y (Mg1.83Al0.88Fe2+ 0.20Li0.08Zn0.01Ti4+ 0.01?0.09) Z (Al5.25?Mg0.75) (BO3)3 Si6O18 V (OH)3? W [F0.87(OH)0.13], with a?=?15.9354(4), c?=?7.1934(4) Å, and they show a significant Al-Mg disorder between the Y and the Z sites (R1?=?0.013–0.015). There is a positive correlation between the Ca content and?<?Y-O?>?distance for all investigated tourmalines (r?≈?1.00), which may reflect short-range order configurations including Ca and Fe2+, Mg, and Li. The tourmalines have XMg (XMg?=?Mg/Mg?+?Fetotal) values in the range 0.84–0.95. The REE patterns show more or less pronounced negative Eu and positive Yb anomalies. In comparison to tourmalines from highly-evolved pegmatites, the tourmaline samples from the border zone of the pegmatites of the Rappold Complex contain relatively low amounts of total REE (~8–36 ppm) and Th (0.1–1.8 ppm) and have low LaN/YbN ratios. There is a positive correlation (r?≈?0.91) between MgO of the tourmalines and the MgO contents of the surrounding mica schists. We conclude that the pegmatites formed by anatectic melting of mica schists and paragneisses in Permian time. The tourmalines crystallized from the pegmatitic melt, influenced by the metacarbonate and metapelitic host rocks. 相似文献
10.
Zhuming Yang Kuishou Ding Jeffrey de Fourestier Qian Mao He Li 《Mineralogy and Petrology》2013,107(2):163-169
The Fe-rich Li-bearing magnesionigerite-6N6S occurs in the Xianghualing tin-polymetallic ore field, Linwu County, Hunan Province, Peoples Republic of China. It was found near the outer contact zone of the Laizhiling granite body and in the Middle-Upper Devonian carbonate rocks of Qiziqiao Formation. The mineral formed during the skarn stage. Its empirical formula is Sn1.81Li0.67(Fe1.43Zn1.19 Mn0.41)Σ3.03(Al14.89Mg1.46 Ti0.11Si0.01)Σ16.47O30(OH)2. The structure for magnesionigerite-6N6S was solved and refined in space group R-3?m, with a?=?5.7144(8), c?=?55.446(11) Å, V?=?1568.0(4) Å3, to R1?=?0.0528. Based on the structural refinement of single crystal diffraction data the formula of magnesionigerite-6N6S is Sn1.80Li0.97(Fe1.89Zn0.91) Σ2.80 (Al14.60Mg1.63 Ti0.20)Σ16.43O30(OH)2 with Z?=?3. Fe-rich Li-bearing magnesionigerite-6N6S contains 0.74 wt.% Li2O. The idealized charge-balanced composition of magnesionigerite-6N6S may be expressed by bivalent and trivalent cations: (Mg2+)4(Al3+)18O30(OH)2. The simplified general formula for the 6N6S polysomes in the nigerite and högbomite groups can be given as A x B18-x O30(OH)2, x?=?~4, where A?=?Mg2+, Fe2+, Zn2+; B?=?Al3+, Sn4+, Ti4+, Li+, □. 相似文献
11.
Reversals for the reaction 2 annite+3 quartz=2 sanidine+3 fayalite+2 H2O have been experimentally determined in cold-seal pressure vessels at pressures of 2, 3, 4 and 5?kbar, limiting annite +quartz stability towards higher temperatures. The equilibrium passes through the temperature intervals 500–540°?C (2?kbar), 550–570°?C (3?kbar), 570–590°?C (4?kbar) and 590–610°?C (5?kbar). Starting materials for most experiments were mixtures of synthetic annite +fayalite+sanidine+quartz and in some runs annite+quartz alone. Microprobe analyses of the reacted mixtures showed that the annites deviate slightly from their ideal Si/Al ratio (Si per formula unit ranges between 2.85 and 2.92, AlVI between 0.06 and 0.15). As determined by Mössbauer spectroscopy, the Fe3+ content of annite in the assemblage annite+fayalite +sanidine+quartz is around 5–7%. The experimental data were used to extract the thermodynamic standard state enthalpy and entropy of annite as follows: H 0 f,?Ann =?5125.896±8.319 [kJ/mol] and S 0 Ann=432.62±8.89 [J/mol/K] (consistent with the Holland and Powell 1990 data set), and H 0 f,Ann =?5130.971±7.939 [kJ/mol] and S 0 Ann=424.02±8.39 [J/mol/K] (consistent with the TWEEQ data base, Berman 1991). The preceeding values are close to the standard state properties derived from hydrogen sensor data of the redox reaction annite=sanidine+magnetite+H 2 (Dachs 1994). The experimental half-reversal of Eugster and Wones (1962) on the annite +quartz breakdown reaction could not be reproduced experimentally (formation of annite from sanidine+fayalite+quartz at 540°?C/1.035?kbar/magnetite-iron buffer) and probable reasons for this discrepancy remain unclear. The extracted thermodynamic standard state properties of annite were used to calculate annite and annite+quartz stabilities for pressures between 2 and 5?kbar. 相似文献
12.
Majorite of bulk composition Mg0.86Fe0.15SiO3 was synthesized at 19 GPa and 1900 °C at an oxygen fugacity close to the Re/ReO2 buffer. Optical absorption spectra of polycrystalline samples were measured from 4000 to 25000cm?1. The following features were observed: (1) Three bands at 4554, 6005 and 8093 cm?1 due to the 5Eg → 5T2g transition of Fe2+ in a distorted dodecahedral site. (2) A band at 9340 cm?1 due to the transition 5T2g → 5Eg of octahedral Fe2+. (3) A band at 22784 cm?1 resulting from Fe3+, probably in an octahedral site (6A1g → 4A1g, 4Eg). (4) A very intense system of Fe2+ → Fe3+ intervalence charge transfer bands which can be modelled by two Gaussian components centered at 16542 and 20128 cm?1. The existence of two components in the charge transfer spectrum could be related to the fact that the tetragonal majorite structure may contain Fe3+ in two different octahedral sites. The crystal field splitting Δ of Fe2+ in dodecahedral coordination is 5717 cm?1. If a splitting of the ground state in the order of 1000 cm?1 is assumed, this yields a crystal field stabilization energy (CFSE) of 3930 cm?1, comparable to the CFSE of Fe2+ in pyrope-rich garnet. However, the splitting of 5T2g is significantly higher than in pyrope. This would be consistent with Fe2+ preferentially occupying the more distorted one of the two dodecahedral sites in the majorite structure. For octahedral Fe2+, Δ= 9340 cm?1 and CFSE=3736 cm?1, assuming negligible splitting of the ground state. 相似文献
13.
T. Arlt T. Armbruster R. Miletich P. Ulmer T. Peters 《Physics and Chemistry of Minerals》1998,26(2):100-106
Single crystals of the garnet Mn2+ 3Mn3+ 2[SiO4]3 and coesite were synthesised from MnO2-SiO2 oxide mixtures at 1000°C and 9 GPa in a multianvil press. The crystal structure of the garnet [space group Ia3¯d, a=11.801(2) Å] was refined at room temperature and 100 K from single-crystal X-ray data to R1=2.36% and R1=2.71%, respectively. In contrast to tetragonal Ca3Mn3+ 2[GeO4]3 (space group I41/a), the high-pressure garnet is cubic and does not display an ordered Jahn-Teller distortion of octahedral Mn3+. A disordered Jahn-Teller distortion either dynamic or static is evidenced by unusual high anisotropic displacement parameters. The room temperature structure is characterised by following bond lengths: Si-O=1.636(4) Å (tetrahedron), Mn3+-O=1.995 (4) Å (octahedron), Mn2+-O=2.280(5) and 2.409(4) Å (dodecahedron). The cubic structure was preserved upon cooling to 100 K [a=11.788(2) Å] and upon compressing up to 11.8 GPa in a diamond-anvil cell. Pressure variation of the unit cell parameter expressed by a third-order Birch-Murnaghan equation of state led to a bulk modulus K 0=151.6(8) GPa and its pressure derivatives K′=6.38(19). The peak positions of the Raman spectrum recorded for Mn2+ 3Mn3+ 2[SiO4]3 were assigned based on a calderite Mn2+ 3Fe3+ 2[SiO4]3 model extrapolated from andradite and grossular literature data. 相似文献
14.
The assignment of spin-allowed Fe2+-bands in orthopyroxene electronic absorption spectra is revised by studying synthetic bronzite (Mg0.8 Fe0.2)2Si2O6, hypersthene (Mg0.5 Fe0.5)2Si2O6 and ferrosilite (Fe2Si2O6). Reheating of bronzite and hypersthene single crystals causes a redistribution of the Fe2+-ions over the M1 and M2 octahedra, which was determined by Mössbauer spectroscopy and correlated to the intensity change of the spin-allowed Fe2+ d-d bands in the polarized absorption spectra. The 11000 cm-1 band is caused by Fe2+ in M1 (5B2g→5A1g) and Fe2+ in M2 (5A1→5A1), the 8500 cm-1 band by Fe2+ in M1 (5B2g→5B1g) and the 5000 cm-1 band by Fe2+ in M2 octahedra (5A1→5B1). The Fe2+-Fe3+ charge transfer band is identified at 12500cm-1 in the spectra of synthetic Fe3+ -Al bearing ferrosilite. This band shows a strong γ-polarization and therefore is caused by Fe2+ -Fe3+-ions in edge-sharing octahedra. 相似文献
15.
Charles A. Geiger Helmut Rager Michael Czank 《Contributions to Mineralogy and Petrology》2000,140(3):344-352
Cordierite has the ideal formula (Mg,Fe)2Al4Si5O18 .x(H2O,CO2), but it must contain some Fe3+ to account for its blue color and strong pleochroism. The site occupation and concentration of Fe3+ in two Mg-rich natural cordierites have been investigated by EPR and 57Fe Mössbauer spectroscopy. In addition, powder IR spectroscopy, X-ray diffraction, and TEM examination were used to characterize the samples. Single-crystal and powder EPR spectra indicate that Fe3+ is located on T11 in natural cordierites and not in the channels. The amount in Mg-rich cordierites is very small with an upper limit set by Mössbauer spectroscopy giving less than 0.004 cations per formula unit (pfu). Fe3+ in cordierite can, therefore, be considered insignificant for most petrologic calculations. Heat-treating cordierite in air at 1,000?°C for 2?days causes an oxidation and/or loss of Fe2+ on T11, together with an expulsion of Na+ from the channels, whereas heating at the Fe–FeO buffer produces little Fe3+ in cordierite. Heating at 1,000?°C removes all class I H2O, but small amounts of class II H2O remain as shown by the IR measurements. No evidence for channel Fe2+ or Fe3+ in the heat-treated samples was found. The blue color in cordierite arises from a broad absorption band (E//b and weaker with E//a) around 18,000?cm?1 originating from charge-transfer between Fe2+ in the octahedron and Fe3+ in the edge-shared T11 tetrahedron. It therefore appears that all natural cordierites contain some tetrahedral Fe3+. The brown color of samples heated in air may be due to the formation of very small amounts of submicroscopic magnetite and possibly hematite. These inclusions in cordierite can only be identified through TEM study. 相似文献
16.
I. V. Pekov N. V. Zubkova D. Yu. Chernyshov M. E. Zelenski V. O. Yapaskurt D. Yu. Pushcharovskii 《Doklady Earth Sciences》2013,448(1):112-116
A new Cu-rich variety of lyonsite has been found from fumarolic sublimates of the Tolbachik volcano (Kamchatka, Russia). The empirical formula is Cu4.33Fe 2.37 3+ Ti0.26Al0.26Zn0.07(V5.85As0.07Mo0.07P0.01S0.01)O24. The crystal structure was studied on single crystal using synchrotron radiation, R = 0.0514. The mineral is orthorhombic, Pnma, a = 5.1736(7), b =10.8929(12), c = 18.220(2) Å, V = 1026.8(2) Å3, and Z = 2. The structural formula is (Cu0.6Ti0.3Al0.3Fe 0.2 3+ □0.6)Σ2Cu2(Fe 2.2 3+ Cu1.8)Σ4(V5.8As0.1Mo0.1)Σ6O24. It is proposed to recast the simplified formula of lyonsite as Cu3+x (Fe 4?2x 3+ Cu2x )(VO4)6, where 0 ≤ x ≤ 1. 相似文献
17.
Juraj Majzlan Tamara Ðorđević Uwe Kolitsch Jürg Schefer 《Mineralogy and Petrology》2010,100(3-4):241-248
Using single-crystal X-ray diffraction at 293, 200 and 100 K, and neutron diffraction at 50 K, we have refined the positions of all atoms, including hydrogen atoms (previously undetermined), in the structure of coquimbite ( $ P {\bar 3}1c $ , a?=?10.924(2)/10.882(2) Å, c?=?17.086(3) / 17.154(3) Å, V?=?1765.8(3)/1759.2(5) Å3, at 293 / 50 K, respectively). The use of neutron diffraction allowed us to determine precise and accurate hydrogen positions. The O–H distances in coquimbite at 50 K vary between 0.98 and 1.01 Å. In addition to H2O molecules coordinated to the Al3+ and Fe3+ ions, there are rings of six “free” H2O molecules in the coquimbite structure. These rings can be visualized as flattened octahedra with the distance between oxygen and the geometric center of the polyhedron of 2.46 Å. The hydrogen-bonding scheme undergoes no changes with decreasing temperature and the unit cell shrinks linearly from 293 to 100 K. A review of the available data on coquimbite and its “dimorph” paracoquimbite indicates that paracoquimbite may form in phases closer to the nominal composition of Fe2(SO4)3·9H2O. Coquimbite, on the other hand, has a composition approximating Fe1.5Al0.5(SO4)3·9H2O. Hence, even a “simple” sulfate Fe2-x Al x (SO4)3·9H2O may be structurally rather complex. 相似文献
18.
Gordon Smith 《Physics and Chemistry of Minerals》1978,3(4):375-383
Reduction of Fe3+ to Fe2+ by heating in hydrogen reduces the absorbance of the bands at 9,000 and 13,800 cm?1 in the E ⊥ c spectrum of tourmaline, and the 9,000 and 11,000 cm?1 bands in the E ∥ (001) spectrum of biotite. This behaviour is consistent with the presumed d-d origin of these bands (which seems well established) only if they gain much of their intensity from exchange-coupling with neighbouring Fe3+ ions. Intensification of spin-forbidden bands in sapphire by Fe3+-Fe3+ exchange-coupling was recognized by Ferguson and Fielding (1971, 1972), but exchange-coupling has not previously been thought to intensify spin-allowed d-d bands. Spin-allowed exchange-coupled bands resulting from Fe2+-Fe3+ pairs have features in common with both normal single ion d-d bands, which they resemble in energy, width and pressure dependence, and Fe2++Fe3+→Fe3++Fe2+ charge transfer bands, which they resemble in temperature-, heat treatment-, composition-, and polarization-dependence. Distinction between normal d-d, charge transfer, and pair d-d absorptions is thus complicated, and criteria for assigning these bands are discussed. Spin-allowed exchange-coupled pair bands should be sought in the spectra of transition metal clusters (trimers and polymers as well as pairs may be involved) whenever geometry favours their origin. It is possible that the bands near 10,000 and 11,500 cm?1 in blue sapphire, and at about 5,000 cm?1 in titanian garnets are of this type, but many other examples are likely to occur. Exchange-coupling may involve ions other than Fe3+ (e.g., Mn2+, also d 5), although Fe2+-Fe2+ coupling is unlikely to be important at laboratory temperatures. 相似文献
19.
Ryosuke Sinmyo Elena Bykova Catherine McCammon Ilya Kupenko Vasily Potapkin Leonid Dubrovinsky 《Physics and Chemistry of Minerals》2014,41(6):409-417
Magnesium silicate perovskite is the predominant phase in the Earth’s lower mantle, and it is well known that incorporation of iron has a strong effect on its crystal structure and physical properties. To constrain the crystal chemistry of (Mg, Fe)SiO3 perovskite more accurately, we synthesized single crystals of Mg0.946(17)Fe0.056(12)Si0.997(16)O3 perovskite at 26 GPa and 2,073 K using a multianvil press and investigated its crystal structure, oxidation state and iron-site occupancy using single-crystal X-ray diffraction and energy-domain Synchrotron Mössbauer Source spectroscopy. Single-crystal refinements indicate that all iron (Fe2+ and Fe3+) substitutes on the A-site only, where \( {\text{Fe}}^{ 3+ } /\Upsigma {\text{Fe}}\sim 20\,\% \) based on Mössbauer spectroscopy. Charge balance likely occurs through a small number of cation vacancies on either the A- or the B-site. The octahedral tilt angle (Φ) calculated for our sample from the refined atomic coordinates is 20.3°, which is 2° higher than the value calculated from the unit-cell parameters (a = 4.7877 Å, b = 4.9480 Å, c = 6.915 Å) which assumes undistorted octahedra. A compilation of all available single-crystal data (atomic coordinates) for (Mg, Fe)(Si, Al)O3 perovskite from the literature shows a smooth increase of Φ with composition that is independent of the nature of cation substitution (e.g., \( {\text{Mg}}^{ 2+ } - {\text{Fe}}^{ 2+ } \) or \( {\text{Mg}}^{ 2+ } {\text{Si}}^{ 4+ } - {\text{Fe}}^{ 3+ } {\text{Al}}^{ 3+ } \) substitution mechanism), contrary to previous observations based on unit-cell parameter calculations. 相似文献
20.
A new single beam microtechnique has been developed for measuring the polarized absorption spectra in the region 44,000-4,000 cm?1. Spectra of a natural garnet (Spess70Alm30), measured by the microtechnique and by conventional macrotechniques, are consistent and thus prove the applicability of the microtechnique described. It is possible to obtain well resolved spectra down to about 13,000 cm?1 with crystals as small as about 10 μm. Thus spectra of crystals obtained in routine high-pressure high-temperature silicate syntheses can be measured. The polarized spectra of Mn3+, Fe3+, Fe2+, and Cr3+ in the following synthetic silicate minerals are presented: piemontite (I), acmite (II), orthoferrosilite (III), and kyanite (IV) or uvarovite (V), respectively. O-Cr3+, O-Mn3+, and O-Fe2+ charge transfer band maxima in the UV region are identified at 38,700 cm?1, in V; at 33,200, 35,300, and 39,000 cm?1, in I; and at 32,800, 35,200, and 37,300 cm?1, in III, respectively. Bands in the region ≦25,000 cm?1 are assigned to spin-allowed and spin-forbidden dd transitions as predicted from crystal field theoretical considerations for the foregoing ions in the respective structures. 相似文献