Abstract
The crystal structure and chemical composition of a crystal of (Mg14−x Cr x )(Si5−x Cr x )O24 (x ≈ 0.30) anhydrous Phase B (Anh-B) synthesized in the model system MgCr2O4–Mg2SiO4 at 12 GPa and 1600 °C have been investigated. The compound was found to be orthorhombic, space group Pmcb, with lattice parameters a = 5.900(1), b = 14.218(2), c = 10.029(2) Å, V = 841.3(2) Å3 and Z = 2. The structure was refined to R 1 = 0.065 using 1492 independent reflections. Chromium was found to substitute for both Mg at the M3 site (with a mean bond distance of 2.145 Å) and Si at the octahedral Si1 site (mean bond distance: 1.856 Å), according to the reaction Mg2+ + Si4+ = 2Cr3+. Such substitutions cause a reduction in the volume of the M3 site and an increase in the volume of the Si-dominant octahedron with respect to the values typically observed for pure Anh-B and Fe2+-bearing Anh-B. Taking into account that Cr3+ is not expected to be Jahn–Teller active, it appears that both the Cr3+–for–Mg and Cr3+–for–Si substitutions in the Anh-B structure decrease the distortion of the octahedra. Electron microprobe analysis gave the Mg13.66(8)Si4.70(6)Cr0.62(4)O24 stoichiometry for the studied phase. The successful synthesis of this phase provides new information for the possible mineral assemblages occurring in the Earth’s deep upper mantle and shed new light on the so-called X discontinuity that has been observed at 275–345 km depth in several subcontinental and subduction zone environments.
Similar content being viewed by others
References
Albee AL, Ray L (1970) Correction factors for electron probe analysis of silicate, oxides, carbonates, phosphates, and sulfates. Anal Chem 48:1408–1414
Allègre JA, Poirier JP, Humler E, Hofmann AW (1995) The chemical composition of the Earth. Earth Plan Sci Lett 134:515–526
Bence AE, Albee AL (1968) Empirical correction factors for the electron microanalysis of silicate and oxides. J Geol 76:382–403
Bindi L, Sirotkina E, Bobrov AV, Irifune T (2014a) Chromium solubility in perovskite at high pressure: the structure of (Mg1–xCrx)(Si1–xCrx)O3 (with x = 0.07) synthesized at 23 GPa and 1600 C. Am Miner 99:866–869
Bindi L, Sirotkina E, Bobrov AV, Irifune T (2014b) X-ray single-crystal structural characterization of MgCr2O4, a post-spinel phase synthesized at 23 GPa and 1600 C. J Phys Chem Solids 75:638–641
Bindi L, Sirotkina E, Bobrov AV, Irifune T (2014c) Chromium solubility in MgSiO3 ilmenite at high pressure. Phys Chem Minerals 41:519–526
Bindi L, Sirotkina E, Bobrov AV, Irifune T (2015) Structural and chemical characterization of Mg[(Cr, Mg)(Si, Mg)]O4, a new post-spinel phase with sixfold-coordinated silicon. Am Miner 100:1633–1636
Boffa Ballaran T, Nestola F, Tribaudino M, Ohashi H (2009) Bulk modulus variation along the diopside-kosmochlor solid solution. Eur J Mineral 21:591–597
Brese NE, O’Keeffe M (1991) Bond-valence parameters for solids. Acta Crystallogr B47:192–197
Finger LW, Ko J, Hazen RM, Gasparik T, Hemley RJ, Prewitt CT, Weidner DJ (1989) Crystal chemistry of Phase B and an anhydrous analogue: implications for water storage in the upper mantle. Nature 341:140–142
Finger LW, Hazen RM, Prewitt CT (1991) Crystal structures of Mg12Si4O19(OH)2 (Phase B) and Mg14Si5O24 (phase AnhB). Am Miner 76:1–7
Ganguly J, Frost DJ (2006) Stability of anhydrous Phase B: experimental studies and implications for phase relations in subducting slab and the X discontinuity in the mantle. J Geophys Res 111:B06203
Hazen RM, Finger LW, Ko J (1992) Crystal chemistry of Fe-bearing anhydrous Phase B: implications for transition zone mineralogy. Am Miner 77:217–220
Herzberg C, Gasparik T (1989) Melting experiments on chondrite at high pressures: stability of anhydrous Phase B. Eos 70:484
Ibers JA, Hamilton WC (eds) (1974) International Tables for X-ray crystallography, vol IV. Kynock, The Netherlands, p 366
Irifune T, Kurio A, Sakamoto S, Inoue T, Sumiya H, Funakoshi K (2004) Formation of pure polycrystalline diamond by direct conversion of graphite at high pressure and high temperature. Phys Earth Planet Inter 143–144:593–600
Katsura T, Ito E (1989) The system Mg2SiO4-Fe2SiO4 at high pressure and temperatures: precise determination of stabilities of olivine, modified spinel, and spinel. J Geophys Res 94:15663–15670
Kesson SE, Ringwood AE (1989) Slab-mantle interactions 2. The formation of diamonds. Chem Geol 78:97–118
O’Neill HStC, Palme H (1998) Composition of the silicate earth: implications for accretion and core formation. In: Jackson I (ed) The Earth’s mantle-composition, structure and evolution. Cambridge University Press, U.K, pp 3–126
Ottonello G, Civalleri B, Ganguly J, Perger WF, Belmonte D, Vetuschi Zuccolini M (2010) Thermo-chemical and thermo-physical properties of the high-pressure phase anhydrous B (Mg14Si5O24): an ab initio all-electron investigation. Am Miner 95:563–573
Oxford Diffraction (2006) CrysAlis RED (Version 1.171.31.2) and ABSPACK in CrysAlis RED. Oxford Diffraction Ltd, Abingdon, Oxfordshire, England
Revenaugh J, Williams Q (2000) The seismic X discontinuity: Observations and modeling, Eos Trans. AGU, 81(48), Fall Meet. Suppl., Abstract S21E − 05
Ringwood AE (1979) Origin of the Earth and Moon. Springer, New York
Robinson K, Gibbs GV, Ribbe PH (1971) Quadratic elongation: a quantitative measure of distortion in coordination polyhedra. Science 172:567–570
Sheldrick GM (2008) A short history of SHELX. Acta Crystallogr A 64:112–122
Sirotkina EA, Bobrov AV, Bindi L, Irifune T (2015) Phase relations and formation of chromium-rich phases in the system Mg4Si4O12–Mg3Cr2Si3O12 at 10–24 GPa and 1600 C. Contr Min Petr 169:2
Stachel T (2001) Diamonds from the asthenosphere and the transition zone. Eur J Min 13:883–892
Stachel T, Harris JW (1997) Diamond precipitation and mantle metasomatism-evidence from the trace element chemistry of silicate inclusions in diamonds from Akwatia, Ghana. Contr Mineral Petrol 129:143–154
Yamada A, Inoue T, Irifune T (2004) Melting of enstatite from 13 to 18 GPa under hydrous conditions. Phys Earth Planet Inter 147:45–56
Acknowledgments
The manuscript took advantage from the revision of Kenneth Collerson and Sabrina Nazzareni. The research was supported by “progetto di Ateneo 2013, University of Firenze” to LB, by C.N.R., Istituto di Geoscienze e Georisorse sezione di Firenze, Italy, the Russian Foundation for Basic Research (Project No. 15-55-50033 YaF) to ES and AB. ES thanks Geodynamics Research Center, Ehime University, Matsuyama, Japan, for support of her visit in 2014. FN thanks the ERC Starting Grant 2012 (Grant agreement No. 307322).
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Bindi, L., Sirotkina, E.A., Bobrov, A.V. et al. Chromium solubility in anhydrous Phase B. Phys Chem Minerals 43, 103–110 (2016). https://doi.org/10.1007/s00269-015-0777-2
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00269-015-0777-2