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American Mineralogist, Volume 97, pages 918–929, 2012 0003-004X/12/0506–918$05.00/DOI: http://dx.doi.org/10.2138/am.2012.4041 918 Europium oxidation state and local structure in silicate glasses M. Rita CiCConi,1,* GabRiele Giuli,1 eleonoRa PaRis,1 WeRneR eRtel-inGRisCh,2 PeteR ulMeR,3 and donald b. dinGWell2 1School of Science and Technology, Geology Division, University of Camerino, Via Gentile III da Varano, I-62032 Camerino, Italy 2Department of Earth and Environmental Sciences, LMU, University of Munich, Theresienstrasse 41/III, D-80333 München

1 Preamble Like many other ideas in chemistry, the concept of oxidation state (OS; or oxidation number, ON), traces its origin prior to the development of the electronic theory of chemical bonding. As a result, and not surprisingly, a lot of ink has been devoted to this subject over the years – not only in attempts to define it clearly and uniquely but also to debate inconsistencies in terms used for it and misconceptions about its meaning. It must be admitted that IUPAC, inadvertently perhaps, may have contributed to some of the debate and polemics. Indeed

processes and laboratory experiments (e.g., Carmichael 1991 ; Kress and Carmichael 1991 ; Herd 2008 ). Many petrological and volcanological applications, such as analysis of glassy melt inclusions in minerals from volcanic rocks or interstitial glass in natural and experimental vesiculated and/or partially crystalline samples, require measurements at high spatial resolutions. There are various techniques for quantifying the Fe oxidation state of silicate glasses, with trade-offs between resolution, error, sample preparation requirements, necessity for standards, and

American Mineralogist, Volume 93, pages 1493–1504, 2008 0003-004X/08/0010–1493$05.00/DOI: 10.2138/am.2008.2795 1493 Amorphous mAteriAls: properties, structure, And durAbility† Oxidation state of iron in hydrous phono-tephritic melts JAn A. schuessler,1,* romAn e. botchArnikov,1 hArAld behrens,1 vAleriA misiti,2 And cArmelA FredA2 1Institut für Mineralogie, Leibniz Universität Hannover, Callinstrasse 3, D-30167 Hannover, Germany 2Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Sismologia e Tettonofisica, Via di Vigna Murata 605, Rome, I

American Mineralogist, Volume 97, pages 476–479, 2012 0003-004X/12/0203–476$05.00/DOI: http://dx.doi.org/10.2138/am.2012.4042 476 Letter Determination of the oxidation state of Cu in substituted Cu-In-Fe-bearing sphalerite via m-XANES spectroscopy NigeL J. Cook,1,* CristiaNa L. CiobaNu,1 JoëL brugger,1,2 barbara etsChmaNN,2 DaryL L. howarD,3 martiN D. De JoNge,3 Chris ryaN,4 aND DaviD PatersoN3 1School of Earth and Environmental Sciences, Centre of Tectonics, Resources and Exploration (TRaX), The University of Adelaide, North Terrace, South Australia

American Mineralogist, Volume 92, pages 873–885, 2007 0003-004X/07/0506–873$05.00/DOI: 10.2138/am.2007.2390 873 INTRODUCTION The difference in the geochemical behavior of Fe2+ and Fe3+ in conjunction with the Fe2+/Fe3+ ratio is an important indicator of the oxygen fugacity during mineral formation. It makes the determination of the Fe oxidation state in minerals a highly sought after aim in earth sciences. SpeciÞ cally, the in situ specia- tion of Fe on the microscale is relevant to geology and material sciences, since geomaterials and synthetic

presence of iron and at high temperatures, Cr2+ is not quenchable because of electron charge transfer with Fe3+ upon cooling. Changes in the oxidation state of transition elements have been predicted to be induced by high pressure (Li et al. 1995) but have not been veri- Þ ed experimentally, even though such changes would be critical for their partitioning behavior during differentiation processes. Also, the valence state of transition elements in ferropericlase is important because these elements play a role in properties such as electrical conductivity (Dobson

1 Preamble Oxidation state (OS) gives the degree of oxidation of an atom in terms of counting electrons. An alternative term «oxidation number» is also used in English. It is largely synonymous with OS, and may be preferred when the value represents a mere parameter or number, rather than being related to chemical systematics or a state of the atom in a compound. It scales trends in redox and acid-base properties, as well as in physical properties such as magnetism, and is a key component when tracking the course of chemical reactions. Thus, the concept of OS is

.A. Adolfsson E. Grins J. 2000 The chalcogenide phosphate apatites Ca 10 (PO 4 6 S, Sr 10 (PO 4 6 S, Ba 10 (PO 4 6 S and Ca 10 (PO 4 6 Se Zeitschrift für Kristallographie—Crystalline Materials 215 226 – 230 Herd, C.D., Borg, L.E., Jones, J.H., and Papike, J.J. (2002) Oxygen fugacity and geochemical variations in the martian basalts: implications for martian basalt petrogenesis and the oxidation state of the upper mantle of Mars. Geochimica et Cosmochimica Acta, 66, 2025–2036. 10.1016/S0016-7037(02)00828-1 Herd C.D. Borg L.E. Jones J.H. Papike J.J. 2002 Oxygen fugacity and

Introduction Sulfur is the third most abundant volatile in magmatic systems released during volcanic eruptions and degassing processes (cf. Faure 1986 ; Métrich and Mandeville 2010 ; Mandeville 2010 ) and is the fundamental chemical anomaly in arc-related magmatic-hydrothermal porphyry-type ore deposits, which are an important source of Cu, Au, Ag, and Mo ( Gustafson and Hunt 1975 ; Candela and Piccoli 2005 ). A growing body of data suggests that the oxidation state of S (e.g., S 2− , S 4+ , S 6+ ) plays a fundamental role in controlling ore metal