Home Physical Sciences Synthesis of a quenchable high-pressure form of magnetite (h-Fe3O4) with composition Fel(Fe2+0.75Mg0.26)Fe2(Fe3+ 0.70Cr0.15Al0.11Si0.04)2O4
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Synthesis of a quenchable high-pressure form of magnetite (h-Fe3O4) with composition Fel(Fe2+0.75Mg0.26)Fe2(Fe3+ 0.70Cr0.15Al0.11Si0.04)2O4

  • Monika Koch-Müller EMAIL logo , Enrico Mugnaioli , Dieter Rhede , Sergio Speziale , Ute Kolb and Richard Wirth
Published/Copyright: November 12, 2014
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American Mineralogist
From the journal American Mineralogist Volume 99 Issue 11-12

Abstract

We report the synthesis of h-magnetite, ideally h-Fe3O4 with considerable amounts of substitutional cations (Cr, Mg, Al, Si) and quenchable to ambient conditions. Two types of experiments were performed at 18 GPa and 1800 °C in a multi-anvil press. In one, we used an oxide mixture with a majoritic stoichiometry Mg1.8Fe1.2(Al1.4Cr0.2Si0.2Mg0.2)Si3O12, with Si and Mg in excess as starting material (MA-367, MA-380). In the second type of experiment (MA-376), we started from an oxide mixture on the composition of the Fe-oxide phase obtained in MA-367. The Fe-oxide phases of both experiments were investigated by electron microprobe and transmission electron microscopy including electron diffraction tomography. Our investigations show that the Fe-oxide phases crystallize in the structure-type of h-magnetite. However, electron diffraction data show that keeping the cell setting from literature, this phase crystallizes in space group Amam and not in space group Bbmm as previously proposed. In the experiment MA-367, the Fe-oxide phase are mutually intergrown with majorite, the major phase of the run products. The formula for h-magnetite in this run was calculated as Fe1(Fe2+ 0.75Mg0.26)Fe2(Fe3+ 0.70 Cr0.15Al0.11Si0.04)2O4. In the experiment on the bulk composition of the Fe-oxide, the main phase was h-magnetite with composition Fe1(Fe2+ 1.02)Fe2(Fe3+ 0.65Cr0.19Al0.13Si0.03)2O4 and traces of nearly pure endmember wadsleyite and stishovite. Our results indicate that the substitution of 20 to 30% of Fe (0.7 to 0.9 atoms per formula unit) by smaller cations favored the preservation of the high-pressure form to ambient conditions. We prove that the h-magnetite-type oxide is also stable in chemical systems more complex than Fe-O. Based on our results, which were obtained at 18 GPa and 1800 °C in a system (MA-367) that is closely related to Fe-enriched oceanic lithospheric material, we suggest that a Fe3O4-rich phase may be present in environments connected to deeply subducted slabs and possibly associated with deep carbonatitic melting. Our observations show that Cr strongly partitions in the oxide phase such that the coexisting silicates are depleted in Cr compared to Fe3O4-free assemblages. This may significantly affect the chemical signature of melts produced in the deep mantle.

Keywords: : Fe-oxide; h-Fe3O4; high pressure; electron transmission microscopy; electron diffraction tomography; electron energy-loss spectroscopy; electron microprobe analyses; crystal chemistry
Received: 2014-2-19
Accepted: 2014-5-26
Published Online: 2014-11-12
Published in Print: 2014-11-1

© 2014 by Walter de Gruyter Berlin/Boston

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https://doi.org/10.2138/am-2014-4944
Keywords for this article
Fe-oxide; h-Fe3O4; high pressure; electron transmission microscopy; electron diffraction tomography; electron energy-loss spectroscopy; electron microprobe analyses; crystal chemistry

Articles in the same Issue

  1. Highlights and Breakthroughs Merrillite and apatite as recorders of planetary magmatic processes
  2. Highlights and Breakthroughs Comparing clays from Mars and Earth: Implications for martian habitability
  3. Data-driven abductive discovery in mineralogy
  4. Thermal expansion of fluorapatite-hydroxylapatite crystalline solutions
  5. Synthesis and structure of carbonated barium and lead fluorapatites: Effect of cation size on A-type carbonate substitution
  6. Optical absorption spectroscopy study of the causes for color variations in natural Fe-bearing gahnite: Insights from iron valency and site distribution data
  7. Si-magnetite nano-precipitates in silician magnetite from banded iron formation: Z-contrast imaging and ab initio study
  8. Ordering kinetics in synthetic Mg(Al,Fe3+)2O4 spinels: Quantitative elucidation of the whole Al-Mg-Fe partitioning, rate constants, activation energies
  9. Experimental study of phlogopite reaction rim formation on olivine in phonolite melts: Kinetics, reaction rates, and residence times
  10. Etch-pit size, dissolution rate, and time in the experimental dissolution of olivine: Implications for estimating olivine lifetime at the surface of Mars
  11. Ferrian saponite from the Santa Monica Mountains (California, U.S.A., Earth): Characterization as an analog for clay minerals on Mars with application to Yellowknife Bay in Gale Crater
  12. A large spectral survey of small lunar craters: Implications for the composition of the lunar mantle
  13. In-situ characterization of oxalic acid breakdown at elevated P and T: Implications for organic C-O-H fluid sources in petrologic experiments
  14. Slawsonite-celsian-hyalophane assemblage from a picrite sill (Prague Basin, Czech Republic)
  15. Determining hematite content from NUV/Vis/NIR spectra: Limits of detection
  16. The role of water in generation of group II kimberlite magmas: Constraints from multiple saturation experiments
  17. Quantum mechanical modeling of hydrolysis and H2O-exchange in Mg-, Ca-, and Nisilicate clusters: Implications for dissolution mechanisms of olivine minerals
  18. Redox-driven exsolution of iron-titanium oxides in magnetite in Miller Range (MIL) 03346 nakhlite: Evidence for post crystallization oxidation in the nakhlite cumulate pile?
  19. Energetics of lanthanide-doped calcium phosphate apatite
  20. Thermal conductivity of molten and glassy NaAlSi3O8, CaMgSi2O6, and Mg2SiO4 by non-equilibrium molecular dynamics at elevated temperature and pressure
  21. Energetics of heterometal substitution in ε-Keggin [MO4Al12(OH)24(OH2)12]6/7/8+ ions
  22. Ab initio calculations of elastic constants of plagioclase feldspars
  23. Diagenetic formation of interlayer-deficient fluorophlogopite as a clay mineral in Early Cambrian phosphorite (Lesser Himalaya, India): The trioctahedral analog of illite
  24. Natural sepiolite: Enthalpies of dehydration, dehydroxylation, and formation derived from thermochemical studies
  25. A new interpretation of decomposition products of serpentine under shock compression
  26. model for calculating the viscosity of natural iron-bearing silicate melts over a wide range of temperatures, pressures, oxygen fugacites, and compositions
  27. The replacement of chalcopyrite by bornite under hydrothermal conditions
  28. Characterization of porosity in sulfide ore minerals: A USANS/SANS study
  29. Synthesis of a quenchable high-pressure form of magnetite (h-Fe3O4) with composition Fel(Fe2+0.75Mg0.26)Fe2(Fe3+ 0.70Cr0.15Al0.11Si0.04)2O4
  30. High-pressure elasticity of sodium majorite garnet, Na2MgSi5O12
  31. Armstrongite from Khan Bogdo (Mongolia): Crystal structure determination and implications for zeolite-like cation exchange properties
  32. Steinhardtite, a new body-centered-cubic allotropic form of aluminum from the Khatyrka CV3 carbonaceous chondrite
  33. New Mineral Names
  34. Book Review
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