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Synthesis and crystal-chemistry of alkali amphiboles in the system Na2O-MgO-FeO-Fe2O3- SiO2-H2O as a function of fO2

  • Giancarlo Della Ventura EMAIL logo , Gianluca Iezzi , Günther J. Redhammer , Frank C. Hawthorne , Bruno Scaillet and Daniela Novembre
Published/Copyright: March 28, 2015
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American Mineralogist
From the journal American Mineralogist Volume 90 Issue 8-9

Abstract

This paper reports the results of hydrothermal synthesis in the system Na2O-MgO-FeO-Fe2O3-SiO2- H2O. Four samples of stoichiometric magnesioriebeckite composition, ideally ◻Na2Mg3Fe23+Si8O22(OH)2, were run at 700-800 °C, 0.4 GPa, and redox conditions varying from NNO (Nickel.Nickel Oxide) to NNO + 2.3 log fO₂. Powder XRD and SEM-EDX show a high (>85%) amphibole yield for all samples; however, in no case was the end-member composition attained. EMP analyses show that the amphiboles obtained deviate strongly from nominal stoichiometry toward magnesio-arfvedsonite [NaNa2Mg4Fe3+Si8O22(OH)2]. Powder XRD patterns were indexed in the space group C2/m; refined cell-parameters reß ect variations in the amphibole composition, and the cell volume is correlated linearly with the A-site occupancy. Mössbauer spectra show that in all samples, Fe3+ is completely ordered at M2, whereas Fe2+ occurs at the M1, M3, and M4 sites. The Fe3+/Fe2+ ratio is a function of fO₂: for increasing oxidation conditions, there is significant increase in M2Fe3+ and decrease in Fe2+, notably in M4Fe2+. Mössbauer spectra also show significant variation in M1Fe2+ and M3Fe2+ quadrupole splitting as a function of the Fe3+ content in the amphibole. IR spectra in the OH-stretching region show a well-resolved quadruplet at frequencies <3680 cm-1, assigned to octahedral M1,3(Mg, Fe2+)-OH-A◻ configurations, and a broad band consisting of four overlapping components related to M1,3(Mg, Fe2+) configurations associated with occupied A-sites. Quantitative evaluation of the relative band intensities suggests a linear increase of A-site occupancy with decreasing fO₂ of synthesis. The composition of the amphiboles synthesized, can be best described by a combination of the C(Mg,Fe2+)1B(Mg,Fe2+)1 CFe3+-1BNa-1 and the ANa1C(Mg,Fe2+)1 A◻-1 CFe3+-1 exchange vectors. The experimental trend is in accord with the trend documented for natural amphiboles, and suggests that the amphibole composition can in fact be used to monitor changes in fO₂ during crystallization

Received: 2004-4-24
Accepted: 2005-2-7
Published Online: 2015-3-28
Published in Print: 2005-8-1

© 2015 by Walter de Gruyter Berlin/Boston

Articles in the same Issue

  1. Crystal-size and shape distributions of magnetite from uncultured magnetotactic bacteria as a potential biomarker
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  17. Compositional zoning in sphalerite crystals
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  22. Early diagenetic origin of Al phosphate-sulfate minerals (woodhouseite and crandallite series) in terrestrial sandstones, Nova Scotia, Canada
  23. Scandium silicates from the Baveno and Cuasso al Monte NYF-granites, Southern Alps (Italy): Mineralogy and genetic inferences
  24. Letter. The effect of Fictive temperature on Al coordination in high-pressure (10 GPa) sodium aluminosilicate glasses
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https://doi.org/10.2138/am.2005.1682

Articles in the same Issue

  1. Crystal-size and shape distributions of magnetite from uncultured magnetotactic bacteria as a potential biomarker
  2. Tourmaline-bearing rocks in the Singhbhum shear zone, eastern India: Evidence of boron infiltration during regional metamorphism
  3. High-resolution transmission electron microscopy (HRTEM) study of the 4a and 6a superstructure of bornite Cu5FeS4
  4. Possible Fe/Cu ordering schemes in the 2a superstructure of bornite (Cu5FeS4)
  5. TEM-specimen preparation of cell/mineral interfaces by Focused Ion Beam milling
  6. Direct observation of spinodal decomposition in the magnetite-hercynite system by susceptibility measurements and transmission electron microscopy
  7. Thermodynamics of uranyl minerals: Enthalpies of formation of rutherfordine, UO2CO3, andersonite, Na2CaUO2(CO3)3(H2O)5, and grimselite, K3NaUO2(CO3)3H2O
  8. Mixing and ordering behavior in manganocolumbite-ferrocolumbite solid solution: A single-crystal X-ray diffraction study
  9. Structure change of MgSiO3, MgGeO3, and MgTiO3 ilmenites under compression
  10. Dehydration processes in the meta-autunite group minerals meta-autunite, metasaléeite, and metatorbernite
  11. Investigation of the martensitic-like transformation from Mg2GeO4 olivine to its spinel structure polymorph
  12. A high-temperature diffraction study of the solid solution CaTiOSiO4-CaTiOGeO4
  13. The vibrational spectrum of synthetic hydrogrossular (katoite) Ca3Al2(O4H4)3: A low-temperature IR and Raman spectroscopic study
  14. Structural characterization of biogenic Mn oxides produced in seawater by the marine bacillus sp. strain SG-1
  15. Investigation of smectite hydration properties by modeling experimental X-ray diffraction patterns: Part I. Montmorillonite hydration properties
  16. Synthesis and crystal-chemistry of alkali amphiboles in the system Na2O-MgO-FeO-Fe2O3- SiO2-H2O as a function of fO2
  17. Compositional zoning in sphalerite crystals
  18. Structure and the extent of disorder in quaternary (Ca-Mg and Ca-Na) aluminosilicate glasses and melts
  19. Makarochkinite, Ca2Fe42+Fe3+TiSi4BeAlO20, a new beryllosilicate member of the aenigmatite-sapphirine-surinamite group from the Ilʼmen Mountains (southern Urals), Russia
  20. Formation of lava stalactites in the master tube of the 1792-1793 flow field, Mt. Etna (Italy)
  21. Crystal-size distributions of garnets in metapelites from the northeastern Bushveld contact aureole, South Africa
  22. Early diagenetic origin of Al phosphate-sulfate minerals (woodhouseite and crandallite series) in terrestrial sandstones, Nova Scotia, Canada
  23. Scandium silicates from the Baveno and Cuasso al Monte NYF-granites, Southern Alps (Italy): Mineralogy and genetic inferences
  24. Letter. The effect of Fictive temperature on Al coordination in high-pressure (10 GPa) sodium aluminosilicate glasses
  25. Letter. α-PbO2-type nanophase of TiO2 from coesite-bearing eclogite in the Dabie Mountains, China
  26. Letter. Morphological characteristics of ordered kaolinite: Investigation using electron back-scattered diffraction
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