57Fe Mössbauer-effect studies of Ca-rich, Fe-bearing clinopyroxenes: Part III. Diopside
-
Eddy De Grave
und
Sigrid G. Eeckhout
Abstract
Three natural Fe-bearing diopside samples, hereafter labeled Dp1, Dp2, and Dp3, have been examined by Mössbauer spectroscopy at temperatures from 4.2-800 K. The Fe contents are 0.01, 0.06, and 0.30 atoms per formula unit (apfu), respectively. All three species contain some Fe in the trivalent state. The spectra are adequately described by a superposition of three quadrupole doublets arising from Fe2+(M1), Fe2+(M2), and Fe3+. The Fe3+ fraction seems to increase with increasing total Fe. The coordination of the ferric ions could not be inferred, but the observed line broadening of the Fe3+ doublet indicates that they possibly substitute at both M1 and M2. The ferrous ions have a strong preference for the M1 sites. For the ferroan diopside sample Dp3 a spectrum at 80 K in an applied field of 60 kOe was recorded to determine the signs and the asymmetry parameters of the electric-field gradient. The signs are all negative and the asymmetry is large (~0.9), implying that an additional distortion is superimposed on the trigonal compression of the polyhedra. The center shifts d for the two Fe2+ sites are equal within experimental error limits. From their temperature variations, equal values for the lattice temperatures, ΘM, and hence for their recoilless fractions, ƒ2, at any given temperature have been deduced. The recoilless fraction, ƒ3, for Fe3+ is higher. The ƒ2/ƒ3 ratio was found to be ~0.95 at 80 K, and decreases with increasing temperature. The temperature variations of the ferrous quadrupole splittings show the importance of spin-orbit coupling. They were calculated from the thermal populations of the 25 electronic levels within the 5D term. The energies of these levels were determined by diagonalization of the complete crystal-field Hamiltonian. For the numerical expression of this Hamiltonian, use was made of the point-charge approach, which takes into account the real point symmetry of the M1 and M2 lattice sites by considering the positions and the effective charges of the various cations and anions in the diopside unit cell. The lattice contribution to the electric-field gradient and the spin-orbit coupling were included. We found that this theoretical treatment yielded excellent results for the M1 sites, correctly predicting the temperature dependencies of the quadrupole splittings for all three diopside species and the high magnitude of the asymmetry parameter. In contrast, the analyses for the M2 sites were less successful. We argue that the failure is due to a lack of correct crystallographic data concerning the coordination of Fe2+ at M2 in diopside.
© 2015 by Walter de Gruyter Berlin/Boston
Artikel in diesem Heft
- Bonding preferences of non-bridging O atoms: Evidence from 17O MAS and 3QMAS NMR on calcium aluminate and low-silica Ca-aluminosilicate glasses
- BNa–BLi solid-solution in A-site-vacant amphiboles: synthesis and cation ordering along the ferri-clinoferroholmquistite–riebeckite join
- A new uranyl carbonate sheet in the crystal structure of fontanite, Ca[(UO2)3(CO3)2O2](H2O)6
- XANES calibrations for the oxidation state of iron in a silicate glass
- Dissolution of strontianite at high P-T conditions: An in-situ synchrotron X-ray fluorescence study
- Intergrown niobian rutile phases with Sc- and W-rich ferrocolumbite: An electron-microprobe and Rietveld study
- Bulk moduli and high-pressure crystal structures of minium, Pb3O4, determined by X-ray powder diffraction
- Slow oxygen diffusion rates in igneous zircons from metamorphic rocks
- Chemistry of grain boundaries in mantle rocks
- Heats of mixing of silicate liquid in the systems diopside-anorthite-akermanite, diopside-anorthite-forsterite, and diopside-silica
- High-pressure crystal structure of kosmochlor, NaCrSi2O6, and systematics of anisotropic compression in pyroxenes
- Monte Carlo simulations of ordering of Al, Fe, and Mg cations in the octahedral sheet of smectites and illites
- Influence of F content on the composition of Al-rich synthetic phlogopite: Part II. Probing the structural arrangement of aluminum in tetrahedral and octahedral layers by 27Al MQMAS and 1H/19F-27Al HETCOR and REDOR experiments
- Dawsonite: An inclusion mineral in quartz from the Tin Mountain pegmatite, Black Hills, South Dakota
- Hydrogen-bonded water in laumontite II: Experimental determination of site-specific thermodynamic properties of hydration of the W1 and W5 sites
- High P-T phase relations and stability of a (21)-hydrous clinopyribole in the system K2ONa2O- CaO-MgO-Al2O3-SiO2-H2O: An experimental study to 18 GPa
- The crystal chemistry of julgoldite-Fe3+ from Bombay, India, studied using synchrotron X-ray powder diffraction and 57Fe Mössbauer spectroscopy
- Partitioning of Sr, Ba, Rb, Y, and LREE between plagioclase and peraluminous silicic magma
- Infrared and TEM characterization of amphiboles synthesized near the tremolite-pargasite join in the ternary system tremolite-pargasite-cummingtonite
- Coupling between non-convergent ordering and transition temperature in the C2/c ↔ P21/c phase transition in pigeonite
- 57Fe Mössbauer-effect studies of Ca-rich, Fe-bearing clinopyroxenes: Part I. Paramagnetic spectra of magnesian hedenbergite
- 57Fe Mössbauer-effect studies of Ca-rich, Fe-bearing clinopyroxenes: Part II. Magnetic spectra of magnesian hedenbergite
- 57Fe Mössbauer-effect studies of Ca-rich, Fe-bearing clinopyroxenes: Part III. Diopside
- Letters. Aluminum substitution in MgSiO3 perovskite: Investigation of multiple mechanisms by 27Al NMR
- Studtite, [(UO2)(O2)(H2O)2](H2O)2: The first structure of a peroxide mineral
- Nanometer-scale measurements of iron oxidation states of cronstedtite from primitive meteorites
Artikel in diesem Heft
- Bonding preferences of non-bridging O atoms: Evidence from 17O MAS and 3QMAS NMR on calcium aluminate and low-silica Ca-aluminosilicate glasses
- BNa–BLi solid-solution in A-site-vacant amphiboles: synthesis and cation ordering along the ferri-clinoferroholmquistite–riebeckite join
- A new uranyl carbonate sheet in the crystal structure of fontanite, Ca[(UO2)3(CO3)2O2](H2O)6
- XANES calibrations for the oxidation state of iron in a silicate glass
- Dissolution of strontianite at high P-T conditions: An in-situ synchrotron X-ray fluorescence study
- Intergrown niobian rutile phases with Sc- and W-rich ferrocolumbite: An electron-microprobe and Rietveld study
- Bulk moduli and high-pressure crystal structures of minium, Pb3O4, determined by X-ray powder diffraction
- Slow oxygen diffusion rates in igneous zircons from metamorphic rocks
- Chemistry of grain boundaries in mantle rocks
- Heats of mixing of silicate liquid in the systems diopside-anorthite-akermanite, diopside-anorthite-forsterite, and diopside-silica
- High-pressure crystal structure of kosmochlor, NaCrSi2O6, and systematics of anisotropic compression in pyroxenes
- Monte Carlo simulations of ordering of Al, Fe, and Mg cations in the octahedral sheet of smectites and illites
- Influence of F content on the composition of Al-rich synthetic phlogopite: Part II. Probing the structural arrangement of aluminum in tetrahedral and octahedral layers by 27Al MQMAS and 1H/19F-27Al HETCOR and REDOR experiments
- Dawsonite: An inclusion mineral in quartz from the Tin Mountain pegmatite, Black Hills, South Dakota
- Hydrogen-bonded water in laumontite II: Experimental determination of site-specific thermodynamic properties of hydration of the W1 and W5 sites
- High P-T phase relations and stability of a (21)-hydrous clinopyribole in the system K2ONa2O- CaO-MgO-Al2O3-SiO2-H2O: An experimental study to 18 GPa
- The crystal chemistry of julgoldite-Fe3+ from Bombay, India, studied using synchrotron X-ray powder diffraction and 57Fe Mössbauer spectroscopy
- Partitioning of Sr, Ba, Rb, Y, and LREE between plagioclase and peraluminous silicic magma
- Infrared and TEM characterization of amphiboles synthesized near the tremolite-pargasite join in the ternary system tremolite-pargasite-cummingtonite
- Coupling between non-convergent ordering and transition temperature in the C2/c ↔ P21/c phase transition in pigeonite
- 57Fe Mössbauer-effect studies of Ca-rich, Fe-bearing clinopyroxenes: Part I. Paramagnetic spectra of magnesian hedenbergite
- 57Fe Mössbauer-effect studies of Ca-rich, Fe-bearing clinopyroxenes: Part II. Magnetic spectra of magnesian hedenbergite
- 57Fe Mössbauer-effect studies of Ca-rich, Fe-bearing clinopyroxenes: Part III. Diopside
- Letters. Aluminum substitution in MgSiO3 perovskite: Investigation of multiple mechanisms by 27Al NMR
- Studtite, [(UO2)(O2)(H2O)2](H2O)2: The first structure of a peroxide mineral
- Nanometer-scale measurements of iron oxidation states of cronstedtite from primitive meteorites
