Skip to content
Licensed Unlicensed Requires Authentication Published by De Gruyter July 2, 2018

The dynamics of Fe oxidation in riebeckite: A model for amphiboles

  • Giancarlo Della Ventura EMAIL logo , Boriana Mihailova , Umberto Susta , Mariangela Cestelli Guidi , Augusto Marcelli , Jochen Schlüter and Roberta Oberti
From the journal American Mineralogist


In this work, we investigate the oxidation behavior of a nearly end-member riebeckite, ideally Na2(Fe32+Fe23+) Si8O22(OH)2, by using vibrational FTIR and Raman spectroscopies. Combining these results with previous studies performed on the same sample by single-crystal structure refinement and Mössbauer spectroscopy, we conclude that iron oxidation in riebeckite is a multi-step process. (1) In the ~523 K < T < 623 K temperature range, the O-H bond lengthens and both the electrons and the hydrogen cations delocalize. Raman analysis shows that this step is reversible upon cooling to room temperature. (2) In the 623 K < T < 723 K range, the kinetic energy increases so that the electrons can be ejected from the crystal; beyond 723 K an irreversible oxidation of Fe occurs that couples with irreversible changes in the SiO4 double-chains leading to a contraction of the unit-cell volume, i.e., to structural changes detectable at the long-range scale. (3) Beyond 823 K, the irreversible oxidation is completed and H+ ions are forced to leave the crystal bulk. Because of this multi-step process, the onset of the deprotonation process is detected at ~700 K by single-crystal XRD analysis of the unit-cell parameters, but starts at 623 K as indicated by Mössbauer spectroscopy on powders (and by changes in the cation distribution observed by structure refinement). Also, Raman scattering shows that the release of H+ from the crystal surface starts ~100 K before the complete deprotonation of the crystal bulk is witnessed by FTIR absorption. Hence, the oxidation of Fe starts at the crystal surface and induces electron and H+ migration from the crystal interior to the rim and thus subsequent oxidation through the crystal bulk. No deprotonation is observed by FTIR either in powders embedded in KBr or in crystals heated in N2 atmosphere, implying that the release of H+ needs surficial (atmospheric) oxygen to form H2O molecules. Fe2+ → Fe3+ oxidation produces a flux of electrons throughout the crystal matrix, which generates electrical conductivity across the amphibole. An important implication of this work, which might have interesting applications in material science, is that iron oxidation in riebeckite (and possibly in other Fe-rich silicates) is reversible in a given range of temperature. Also, this work shows that complex processes cannot be fully understood or even monitored accurately without using a proper combination of independent techniques.


Financial support by the Deutsche Forschungsgemeinschaft (1127/7-2) to B.M. and J.S. is gratefully acknowledged. Thanks are due to Thomas Malcherek (Hamburg), for verifying the crystallinity and determining the crystallographic orientation of the samples that were subjected to in situ high-temperature Raman spectroscopy. Positive criticism of D. Jenkins and M.D. Dyar improved the clarity of our manuscript.

References cited

Addison, W.E., and Sharp, J.H. (1962) Amphiboles. Part III. The reduction of crocidolite. Journal of the Chemical Society, 3693–3698.10.1039/jr9620003693Search in Google Scholar

Addison, W.E., and Sharp, J.H. (1968) Redox behavior of iron in hydroxylated silicates. Eleventh Conference on Clays and Clay Minerals. Abstracts, 95–104.Search in Google Scholar

Addison, W.E., and White, A.D. (1968) The oxidation of Bolivian crocidolite. Mineralogical Magazine, 36, 791–796.10.1180/minmag.1968.036.282.05Search in Google Scholar

Addison, C.C., Addison, W.E., Neal, G.H., and Sharp, J.H. (1962a) Amphiboles. Part I. The oxidation of crocidolite. Journal of the Chemical Society, 1468–1471.10.1039/jr9620001468Search in Google Scholar

Addison, W.E., Neal, G.H., and Sharp, J.H. (1962b) Amphiboles. Part II. The kinetics of oxidation of crocidolite. Journal of the Chemical Society, 1472–1475.10.1039/jr9620001472Search in Google Scholar

Aines, R.D., and Rossman, G.R. (1985) The high temperature behaviour of trace hydrous components in silicate minerals. American Mineralogist, 70, 1169–1179.Search in Google Scholar

Clowe, C.A., Popp, R.K., and Fritz, S.J. (1988) Experimental investigation of the effect of oxygen fugacity on ferric-ferrous ratios and unit-cell parameters of four natural clinoamphiboles. American Mineralogist, 73, 487–499.Search in Google Scholar

Della Ventura, G., Marcelli, A., and Bellatreccia, F. (2014) SR-FTIR microscopy and FTIR imaging in the Earth Sciences. Reviews in Mineralogy and Geochemistry, 78, 447–479.10.2138/rmg.2014.78.11Search in Google Scholar

Della Ventura, G., Radica, F., Bellatreccia, F., Freda, C., and Cestelli Guidi, M. (2015a) Speciation and diffusion profiles of H2O in water-poor beryl: comparison with cordierite. Physics and Chemistry of Minerals, 42, 735–745.10.1007/s00269-015-0758-5Search in Google Scholar

Della Ventura, G., Radica, F., Bellatreccia, F., Cavallo, A., Cinque, G., Tortora, L., and Behrens, H. (2015b) FTIR imaging in diffusion studies: CO2 and H2O in a synthetic sector-zoned beryl. Frontiers in Earth Science, 33, 10.3389/feart.2015.00033.Search in Google Scholar

Della Ventura, G., Susta, U., Bellatreccia, F., Marcelli, A., Redhammer, G., and Oberti, R. (2017) Deprotonation of Fe-dominant amphiboles: Single-crystal HT-FTIR spectroscopic studies of synthetic potassic-ferro-richterite. American Mineralogist, 102, 117–125.10.2138/am-2017-5859Search in Google Scholar

Dowty, E. (1987) Vibrational interactions of tetrahedra in silicate glasses and crystals. II. Calculations on melilites, pyroxenes, silica polymorphs and feldspars. Physics and Chemistry of Minerals, 14, 122–138.10.1007/BF00308216Search in Google Scholar

Dyar, M.D., Mackwell, S.J., McGuire, A.V., Cross, L.R., and Robertson, J.D. (1993) Crystal chemistry of Fe3+ and H+ in mantle kaersutite: Implications for mantle metasomatism. American Mineralogist, 78, 968–979.Search in Google Scholar

Ernst, W.G., and Wai, M. (1970) Mössbauer, infrared, X-ray and optical study of cation ordering and dehydrogenation in natural and heat-treated sodic amphiboles. American Mineralogist, 55, 1226–1258.Search in Google Scholar

Hawthorne, F.C., and Oberti, R. (2007) Amphiboles: Crystal-chemistry. Reviews in Mineralogy and Geochemistry, 67, 1–54.10.1515/9781501508523-002Search in Google Scholar

Hawthorne, F.C., Oberti, R., Harlow, G.E., Maresch, W.V., Martin, R.F., Schumacher, J.C., and Welch, M.D. (2012) Nomenclature of the amphibole supergroup. American Mineralogist, 97, 2031–2048.10.2138/am.2012.4276Search in Google Scholar

Hodgson, A.A., Freeman, A.G., and Taylor, H.F.V. (1965) The thermal decomposition of crocidolite from Koegas, South Africa. Mineralogical Magazine, 35, 5–29.10.1180/minmag.1965.035.269.04Search in Google Scholar

Leissner, L., Schlüter, J., Horn, I., and Mihailova, B. (2015) Exploring the potential of Raman spectroscopy for crystallochemical analysis of complex hydrous silicates: I. Amphiboles. American Mineralogist, 100, 2682–2694.10.2138/am-2015-5323Search in Google Scholar

Momma, K., and Izumi, F. (2008) VESTA: a three-dimensional visulization system for electronic and structural analysis. Journal of Applied Crystallography, 41, 653–658.10.1107/S0021889808012016Search in Google Scholar

Oberti, R., Boiocchi, M., Zema, M., and Della Ventura, G. (2016) Synthetic potassic-ferro-richterite: 1. Composition, crystal structure refinement and HT behavior by in operando single-crystal X-ray diffraction. Canadian Mineralogist, 54, 353–369.10.3749/canmin.1500073Search in Google Scholar

Oberti, R., Boiocchi, M., Zema, M., Hawthorne, F.C., Redhammer, G.J., Susta, U., Della Ventura, G. (2018) The high-temperature behaviour of riebeckite: Expansivity, deprotonation, Fe oxidation and a novel cation disorder scheme. European Journal of Mineralogy, 10.1127/ejm/2018/0030-2712.Search in Google Scholar

Phillips, M.W., Popp, R.K., and Clowe, C.A. (1988) Structural adjustments accompanying oxidation-dehydrogenation in amphiboles. American Mineralogist, 73, 500–506.Search in Google Scholar

Phillips, M.W., Draheim, J.E., Popp, R.K., Clowe, C.A., and Pinkerton, A.A. (1989) Effect of oxidation-dehydrogenation in tschermakitic hornblende. American Mineralogist, 74, 764–773.Search in Google Scholar

Phillips, M.W., Popp, R.K., and Clowe, C.A. (1991) A structural investigation of oxidation effects in air-heated grunerite. American Mineralogist, 76, 1502–1509.Search in Google Scholar

Popp, R.K., Phillips, M.W., and Harrell, J.A. (1990) Accomodation of Fe3+ in natural Fe3+-rich calcic and subcalcic amphiboles: Evidence from published chemical analyses. American Mineralogist, 75, 163–169.Search in Google Scholar

Schmidbauer, E., Kunzmann, Th., Fehr, Th., and Hochleitner, R. (1996) Electrical conductivity, thermopower and 57Fe Mössbauer spectroscopy on an Fe-rich amphibole, arfvedsonite. Physics and Chemistry of Minerals, 23, 99–106.10.1007/BF00202305Search in Google Scholar

Susta, U., Della Ventura, G., Hawthorne, F.C., Abdu, Y.A., Day, M.C., Mihailova, B., and Oberti, R. (2018) The crystal-chemistry of riebeckite, ideally Na2Fe32+Fe23+ Si8O22(OH)2: a multidisciplinary study. Mineralogical Magazine, 10.1180/minmag.2017.081.064.Search in Google Scholar

Turci, F., Tomatis, M., and Pacella, A. (2017) Surface and bulk properties of mineral fibres relevant to toxicity. In A.F. Gualtieri, Ed., Mineral Fibres: Crystal chemistry, chemical physical properties, biological interaction and toxicity. EMU Notes in Mineralogy, 18, 171–214.Search in Google Scholar

Ungaretti, L. (1980) Recent developments in X-ray single crystal diffractometry applied to the crystal-chemical study of amphiboles. Godisnjak Jugonslavenskog Centra za Kristalografiju, 15, 29–65.Search in Google Scholar

Wang, D., Guo, Y., Yu, Y., and Karato, S. (2012) Electrical conductivity of amphibole-bearing rocks: influence of dehydration. Contributions to Mineralogy and Petrology, 164, 17–25.10.1007/s00410-012-0722-zSearch in Google Scholar

Watenphul, A., Malcherek, T., Wilke, F., Schlüter, J., and Mihailova, B. (2017) Composition-thermal expandability relations and oxidation processes in tourmaline studied by in-situ Raman spectroscopy. Physics and Chemistry of Minerals, 44, 735–748.10.1007/s00269-017-0894-1Search in Google Scholar

Zhang, M., Wang, L., Hirai, S., Redfern, S.A., and Salje, E.K.H. (2005) Dehydrohylation and CO2 incorporation in annealed mica (sericite): an infrared spectroscopic study. American Mineralogist, 90, 173–180.10.2138/am.2005.1615Search in Google Scholar

Zhang, M., Hui, Q., Lou, X.J., Redfern, S.A., Salje, E.K.H., and Tarantino, S.C. (2006) Dehydrohylation, proton migration, and structural changes in heated talc: an infrared spectroscopic study. American Mineralogist, 91, 816–825.10.2138/am.2006.1945Search in Google Scholar

Received: 2017-11-14
Accepted: 2018-03-10
Published Online: 2018-07-02
Published in Print: 2018-07-26

© 2018 Walter de Gruyter GmbH, Berlin/Boston

Downloaded on 27.3.2023 from
Scroll Up Arrow