Structural variation of babingtonite depending on cation distribution at the octahedral sites     

Mariko Nagashima  Keiko Mitani  Masahide Akasaka 《Mineralogy and Petrology》2014,108(2):287-301

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) ų. 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   

The crystal structure of ilinskite, NaCu5O2(SeO3)2Cl3, and review of mixed-ligand CuOmCln coordination geometries in minerals and inorganic compounds     

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) ų, Z?=?4. The The CuO_mCl_n 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 CuO_mCl_n 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   

Spectroscopic active IVFe3+–VIFe3+ clusters in spinel–magnesioferrite solid solution crystals: a potential monitor for ordering in oxide spinels     

G. B. Andreozzi  U. Hålenius  H. Skogby 《Physics and Chemistry of Minerals》2001,28(7):435-444

Optical absorption spectra (OAS) of synthetic single crystals of the solid solution spinel sensu stricto (s.s.)–magnesioferrite, Mg(Fe³⁺Al_1???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 α_net value of the absorption band at 21 300?cm^?1 and [^IVFe³⁺]?·?[^VIFe³⁺] concentration product has been defined: α_net=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   

Equation of state of Fe3+-bearing phase-X     

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, (K_1.307Na_0.015)(Mg_1.504Fe _0.373 ³⁺ Al_0.053Ti _0.004 ⁴⁺ )Si₂O₇H_0.36, 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 β_0c :β_0a ?=?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   

Plumboselite, Pb3O2(SeO3), a new oxidation-zone mineral from Tsumeb, Namibia     

Anthony R. Kampf  Stuart J. Mills  William W. Pinch 《Mineralogy and Petrology》2011,101(1-2):75-80

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 Pb_2.92Ca_0.01Se_1.03O₅. 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   

The crystal chemistry of lithium and Fe3+ in synthetic orthopyroxene     

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(Mg_0.59Fe _0.21 ²⁺ Li_0.20) ^M1(Mg_0.74Fe _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   

Microscope-photometric methods for non-destructive Fe²⁺ – Fe³⁺ determination in chloritoids (Fe²⁺, Mn²⁺, Mg)₂ (Al,Fe³⁺)₄ Si₂O₁₀(OH)₄     

Ulf Hålenius  Klaus Langer 《Lithos》1980,13(3):291-294

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(I_0/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   

Li-bearing, disordered Mg-rich tourmaline from a pegmatite-marble contact in the Austroalpine basement units (Styria, Austria)     

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 (Na_0.67Ca_0.19?K_0.02?_0.12) ^Y (Mg_1.26Al_0.97Fe²⁺ _0.36Li_0.19Ti⁴⁺ _0.06Zn_0.01?_0.15) ^Z (Al_5.31?Mg_0.69) (BO₃)₃ Si₆O₁₈ ^V (OH)₃? ^W [F_0.66(OH)_0.34], with a?=?15.9220(3), c?=?7.1732(2) Å to ^X (Na_0.67Ca_0.24?K_0.02?_0.07) ^Y (Mg_1.83Al_0.88Fe²⁺ _0.20Li_0.08Zn_0.01Ti⁴⁺ _0.01?_0.09) ^Z (Al_5.25?Mg_0.75) (BO₃)₃ Si₆O₁₈ ^V (OH)₃? ^W [F_0.87(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 X_Mg (X_Mg?=?Mg/Mg?+?Fe_total) 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 La_N/Yb_N 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   

Structure and Mössbauer spectroscopy of barbosalite Fe2+Fe3+ 2 (PO4)2(OH)2 between 80 K and 300 K     

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 V_zz, 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   

Fe-rich Li-bearing magnesionigerite-6N6S from Xianghualing tin-polymetallic orefield, Hunan Province, P.R. China     

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 Sn_1.81Li_0.67(Fe_1.43Zn_1.19 Mn_0.41)_Σ3.03(Al_14.89Mg_1.46 Ti_0.11Si_0.01)_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) ų, to R1?=?0.0528. Based on the structural refinement of single crystal diffraction data the formula of magnesionigerite-6N6S is Sn_1.80Li_0.97(Fe_1.89Zn_0.91) _Σ2.80 (Al_14.60Mg_1.63 Ti_0.20)_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 B_18-x O₃₀(OH)₂, x?=?~4, where A?=?Mg²⁺, Fe²⁺, Zn²⁺; B?=?Al³⁺, Sn⁴⁺, Ti⁴⁺, Li⁺, □.  相似文献   

The stability of annite+quartz: reversed experimental data for the reaction 2 annite+3 quartz=2 sanidine+3 fayalite +2 H2O     

E. Dachs  Artur Benisek 《Contributions to Mineralogy and Petrology》1995,121(4):380-387

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, Al^VI 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   

High pressure single-crystal synthesis, structure and compressibility of the garnet Mn2+ 3Mn3+ 2[SiO4]3     

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   

Crystal field and charge transfer spectrum of (Mg, Fe)SiO3 majorite     

Hans Keppler  Catherine A. McCammon 《Physics and Chemistry of Minerals》1996,23(2):94-98

Majorite of bulk composition Mg_0.86Fe_0.15SiO₃ 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 ⁵E_g → ⁵T_2g transition of Fe²⁺ in a distorted dodecahedral site. (2) A band at 9340 cm^?1 due to the transition ⁵T_2g → ⁵E_g of octahedral Fe²⁺. (3) A band at 22784 cm^?1 resulting from Fe³⁺, probably in an octahedral site (⁶A_1g → ⁴A_1g, ⁴E_g). (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 ⁵T_2g 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   

Polarized electronic absorption spectra of synthetic (Mg,Fe)-orthopyroxenes,ferrosilite and Fe3+-bearing ferrosilite     

G. Steffen  K. Langer  F. Seifert 《Physics and Chemistry of Minerals》1988,16(2):120-129

The assignment of spin-allowed Fe²⁺-bands in orthopyroxene electronic absorption spectra is revised by studying synthetic bronzite (Mg_0.8 Fe_0.2)₂Si₂O₆, hypersthene (Mg_0.5 Fe_0.5)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 (⁵B_2g→⁵A_1g) and Fe²⁺ in M2 (⁵A₁→⁵A₁), the 8500 cm^-1 band by Fe²⁺ in M1 (⁵B_2g→⁵B_1g) 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   

Cordierite III: the site occupation and concentration of Fe3+     

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   

A new Cu-rich variety of lyonsite from fumarolic sublimates of the Tolbachik volcano (Kamchatka, Russia) and its crystal structure     

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 Cu_4.33Fe _2.37 ³⁺ Ti_0.26Al_0.26Zn_0.07(V_5.85As_0.07Mo_0.07P_0.01S_0.01)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) ų, and Z = 2. The structural formula is (Cu_0.6Ti_0.3Al_0.3Fe _0.2 ³⁺ □_0.6)_Σ2Cu₂(Fe _2.2 ³⁺ Cu_1.8)_Σ4(V_5.8As_0.1Mo_0.1)_Σ6O₂₄. It is proposed to recast the simplified formula of lyonsite as Cu_3+x (Fe _4?2x ³⁺ Cu_2x )(VO₄)₆, where 0 ≤ x ≤ 1.  相似文献   

Hydrogen bonding in coquimbite, nominally Fe2(SO4)3·9H2O, and the relationship between coquimbite and paracoquimbite     

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) ų, 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 Fe_1.5Al_0.5(SO₄)₃·9H₂O. Hence, even a “simple” sulfate Fe_2-x Al _x (SO₄)₃·9H₂O may be structurally rather complex.  相似文献   

Evidence for absorption by exchange-coupled Fe2+-Fe3+ pairs in the near infra-red spectra of minerals     

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   

Crystal chemistry of Fe3+-bearing (Mg,Fe)SiO3 perovskite: a single-crystal X-ray diffraction study     

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 Mg_0.946(17)Fe_0.056(12)Si_0.997(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   

Synthetic Mn3+-kyanite and viridine, (Al2-xMn x 3+ ) SiO5, in the system Al2O3-MnO-MnO2-SiO2     

I. Abs-Wurmbach  Prof. Dr. K. Langer 《Contributions to Mineralogy and Petrology》1975,49(1):21-38

Experiments on the join Al₂SiO₅-“Mn₂SiO₅” of the system Al₂O₃-SiO₂-MnO-MnO₂ in the pressure/temperature range 10–20 kb/900–1050° C with gem quality andalusite, Mn₂O₃, and high purity SiO₂ as starting materials and using /_O2-buffer techniques to preserve the Mn³⁺ oxidation state had following results: At 20 kb/1000°C orange-yellow kyanite mixed crystals are formed. The kyanite solid solubility is limited at about (Al_1.88Mn _0.12 ³⁺ )SiO₅ and, thus, equals approximately that on the join Al₂SiO₅-“Fe₂SiO₅” (Langer and Frentrup, 1973) indicating that there is no Jahn-Teller stabilisation of Mn³⁺ in the kyanite matrix. 5 mole % substitution causes the kyanite lattice constants a _o, b _o, c _o, and V _o to increase by 0.015, 0.009, 0.014 Å, and 1.6 ų, resp., while α, β, γ, remain unchanged. Between 10 and 18 kb/900°C, Mn³⁺-substituted, strongly pleochroitic (emeraldgreen-yellow) andalusite_ss (viridine) was obtained. At 15 kb/900°C, the viridine compositional range is about (Al_1.86Mn _0.14 ³⁺ )SiO₅-(Al_1.56Mn _0,44 ³⁺ )SiO₅. Thus, Al→Mn³⁺ substitutional degrees are appreciably higher in andalusite than in kyanite, proving a strong Jahn-Teller effect of Mn³⁺ in the andalusite structure, which stabilises this structure type at the expense of kyanite and sillimanite and, thus, enlarges its PT-stability range extremely. 17 mole % substitution cause the andalusite constants a _o, b _o, c _o, and V _o to increase by 0.118, 0.029, 0.047 Å and 9.4 ų, resp. At “Mn₂SiO₅”-contents smaller than about 7 mole %, viridine coexists with Mn-poor kyanite. At “Mn₂SiO₅”-concentrations higher than the maximum kyanite or viridine miscibility, braunite (tetragonal, ideal formula Mn²⁺Mn³⁺[O₈/Si0₄]), pyrolusite and SiO₂ were found to coexist with the Mn³⁺-saturated ky _ss or and _ss, respectively. In both cases, braunites were Al-substituted (about 1 Al for 1 Mn³⁺). Pure synthetic braunites had the lattice constants a _o 9.425, c _o, 18.700 Å, V _o 1661.1 ų (ideal compn.) and a _o 9.374, c _o 18.593 ų, V _o 1633.6 ų (1 Al for 1 Mn³⁺). Stable coexistence of the Mn²⁺-bearing phase braunite with the Mn⁴⁺-bearing phase pyrolusite was proved by runs in the limiting system MnO-MnO₂-SiO₂.  相似文献