Site occupancies of minor elements in synthetic olivines as determined by channeling-enhanced X-ray emission

McCormick, Tamsin C.; Smyth, Joseph R.; Lofgren, G. E.

doi:10.1007/bf00309812

Cited by 22 publications

(13 citation statements)

References 6 publications

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“…It follows from the simulation results that the M1 site is energetically more favorable for monovalent than that in M1, in accordance with experimental evidence that Ca and Mn ions substitute for Mg primarily on the M2 site [37,38]. According to our calculations, trivalent impurities must preferentially occupy the M2 site.…”

Section: Computer Simulation Of Defectssupporting

confidence: 90%

Crystal-Melt Partition Coefficients of Impurities in Forsterite, Mg2SiO4: Experimental Determination, Crystal-Chemical Analysis, and Thermodynamic Evaluation

2005

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The forsterite-melt partition coefficients ä are determined experimentally for a large number of mono-, di-, tri-, and tetravalent impurities. The energies of native defects and impurities ( E d ) and the solution energies ( E s ) of impurities in forsterite are evaluated using computer simulation. The defect energy is shown to vary linearly with the difference in ionic radius between the host and substituent atoms ( ∆ r ) and with the impurity cation charge, while the partition coefficient and solution energy of impurities are quadratic functions of these parameters. The plots of ln K versus ( ∆ r ) 2 and E s versus ( ∆ r ) 2 for isovalent substitutions ( and ) pass close to the origin, in contrast to the plots for heterovalent substitutions ( and ). The significant y intercept of the latter plots is interpreted as evidence for the formation of extra defects maintaining electroneutrality. The y intercept of the plot of E s versus ( ∆ r ) 2 is 2 eV, which is about half the formation energy of Frenkel defects in forsterite. The best fit equations representing the correlation between the partition coefficients and solution energies of impurities demonstrate that heterovalent substitutions increase the entropy contribution to the free energy of solution of impurities. Me Mg × Me Si × Me Mg ' Me Si . 628 INORGANIC MATERIALS Vol. 41 No. 6 2005 DUDNIKOVA et al .

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Section: Computer Simulation Of Defectssupporting

confidence: 90%

Crystal-Melt Partition Coefficients of Impurities in Forsterite, Mg2SiO4: Experimental Determination, Crystal-Chemical Analysis, and Thermodynamic Evaluation

2005

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“…Polarized optical absorption spectroscopy results additionally agree on the M1 preference of this cation (Taran and Rossman 2001). Confirmation of the M2 site preference of Mn 2+ has been provided by channeling-enhanced X-ray emission spectroscopy (McCormick et al 1987). The effects of temperature on transition metal site occupancies in olivines have been extensively studied by XRD and other methods for samples typically in the range of about 10 to 50% of the non-forsterite component, and have been analyzed thermodynamically, demonstrating systematically increasing M1 preference from Fe 2+ to Co 2+ to Ni 2+ Morozov et al 2006;Heinemann et al 2007).…”

mentioning

confidence: 52%

Transition metal cation site preferences in forsterite (Mg₂SiO₄) determined from paramagnetically shifted NMR resonances

McCarty¹,

Palke²,

Stebbins³

et al. 2015

American Mineralogist

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In marked contrast to the single, narrow 29 Si MAS NMR resonance for pure forsterite (Mg 2 SiO 4 ), the spectra for synthetic forsterite containing 0.05 to 5% of the Mg 2+ replaced with Ni 2+ , Co 2+ , or Fe 2+ display between 4 and 26 additional, small, paramagnetically shifted peaks that are caused by interactions of the unpaired electron spins on the transition metal cations and the nuclear spins. Analyses of these relative peak areas, their numbers, and comparison of their positions to those in spectra of synthetic monticellites (CaMgSiO 4 ) containing similar levels of transition metals, allows at least partial assignment to the effects of cations in either the M1 octahedral site only or to both M1 and M2 sites. More detailed analyses indicate that in forsterite, Ni 2+ occupies only M1, Fe 2+ occupies M1 and M2 roughly equally, and Co 2+ occupies both M1 and M2 in an approximately 3:1 ratio. These findings for low concentrations agree with expectations from previous studies by other methods (e.g., XRD) of olivines with much higher transition metal cation contents. However, even low concentrations of Mn 2+ (e.g., 0.1%), as well as higher Fe 2+ contents (e.g., in natural San Carlos olivine) can broaden NMR peaks sufficiently to greatly reduce this kind of information content in spectra.

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“…() concluded that this peak is assigned to Mn almost certainly in octahedral coordination and probably concentrated in the M2 site (McCormick et al. ), compared with synthetic Mn‐doped forsterite (Steele ). In principle, the emission should differ between Mn sited on M1 and M2, and the position and shape of the emission peaks may reflect site occupancy factors.…”

Section: Discussionmentioning

confidence: 99%

Cathodoluminescence microscopy and spectroscopy of forsterite from Kaba meteorite: An application to the study of hydrothermal alteration of parent body

Gucsik

Endo

Nishido

et al. 2013

Meteorit & Planetary Scien

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Abstract-Highly forsteritic olivine (Fo: 99.2-99.7) in the Kaba meteorite emits bright cathodoluminescence (CL). CL spectra of red luminescent forsterite grains have two broad emission bands at approximately 630 nm (impurity center of divalent Mn ions) in the red region and above 700 nm (trivalent Cr ions) in the red-IR region. The cores of the grains show CL blue luminescence giving a characteristic broad band emission at 400 nm, also associated with minor red emissions related to Mn and Cr ions. CL color variation of Kaba forsterite is attributed to structural defects. Electron probe microanalyzer (EPMA) analysis shows concentrations of Ca, Al, and Ti in the center of the forsterite grain. The migration of diffusible ions of Mn, Cr, and Fe to the rim of the Kaba meteoritic forsterite was controlled by the hydrothermal alteration at relatively low temperature (estimated at about 250°C), while Ca and Al ions might still lie in the core. A very unusual phase of FeO (w€ ustite) was also observed, which may be a terrestrial alteration product of FeNi-metal.

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Site occupancies of minor elements in synthetic olivines as determined by channeling-enhanced X-ray emission

Cited by 22 publications

References 6 publications

Crystal-Melt Partition Coefficients of Impurities in Forsterite, Mg2SiO4: Experimental Determination, Crystal-Chemical Analysis, and Thermodynamic Evaluation

Crystal-Melt Partition Coefficients of Impurities in Forsterite, Mg2SiO4: Experimental Determination, Crystal-Chemical Analysis, and Thermodynamic Evaluation

Transition metal cation site preferences in forsterite (Mg₂SiO₄) determined from paramagnetically shifted NMR resonances

Cathodoluminescence microscopy and spectroscopy of forsterite from Kaba meteorite: An application to the study of hydrothermal alteration of parent body

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Site occupancies of minor elements in synthetic olivines as determined by channeling-enhanced X-ray emission

Cited by 22 publications

References 6 publications

Crystal-Melt Partition Coefficients of Impurities in Forsterite, Mg2SiO4: Experimental Determination, Crystal-Chemical Analysis, and Thermodynamic Evaluation

Crystal-Melt Partition Coefficients of Impurities in Forsterite, Mg2SiO4: Experimental Determination, Crystal-Chemical Analysis, and Thermodynamic Evaluation

Transition metal cation site preferences in forsterite (Mg2SiO4) determined from paramagnetically shifted NMR resonances

Cathodoluminescence microscopy and spectroscopy of forsterite from Kaba meteorite: An application to the study of hydrothermal alteration of parent body

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Transition metal cation site preferences in forsterite (Mg₂SiO₄) determined from paramagnetically shifted NMR resonances