High-T behaviour of gedrite: thermoelasticity, cation ordering and dehydrogenation

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• 作者：Michele Zema (12)
  Mark D. Welch (3) mdw@nhm.ac.uk
  Roberta Oberti (2)
• 关键词：Gedrite &#8211 ; Thermoelasticity &#8211 ; Dehydrogenation &#8211 ; Cation ordering &#8211 ; Single ; crystal X ; ray diffraction at high ; T
• 刊名：Contributions to Mineralogy and Petrology
• 出版年：2012
• 出版时间：May 2012
• 年：2012
• 卷：163
• 期：5
• 页码：923-937
• 全文大小：680.7 KB
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  14. Oberti R (2010) HT behaviour and dehydrogenation processes in monoclinic and orthorhombic amphiboles of petrogenetic relevance. Acta Miner Petrogr 6:147
  15. Oberti R, Hawthorne FC, Cannillo E, C谩mara F (2007) Long-range order in amphiboles. Rev Miner Geochem 67:125–172
  16. Oberti R, Zema M, Boiocchi M, Tarantino S, Zanetti A (2009) A thermal expansion dehydrogenation processes in kaersutites: II—models at the atomic scale. Epitome 3:25
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  18. Reece JJ, Redfern SAT, Welch MD, Henderson CMB (2000) Mn–Mg disordering in cummingtonite: a high temperature neutron powder diffraction study. Miner Mag 64:255–266
  19. Reece JJ, Redfern SAT, Welch MD, Henderson CMB, McCammon CA (2002) Temperature-dependent Fe2+–Mn2+ order–disorder behaviour in amphiboles. Phys Chem Miner 29:562–570
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  22. Schindler M, Sokolova E, Abdu Y, Hawthorne FC, Evans BE, Ishida K (2008) The crystal-chemistry of the gedrite-group amphiboles. I. Crystal structure and site populations. Miner Mag 72:703–730
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  26. Welch MD, Reece JJ, Redfern SAT (2008) Rapid intracrystalline exchange of divalent cations in amphiboles: a high-temperature neutron diffraction study of synthetic K-richterite AK B(NaCa) C(Mg2.5Ni2.5) Si8 O22 (OH)2. Miner Mag 72:877–886
  27. Welch MD, C谩mara F, Oberti R (2011) Thermoelasticity and high-T behaviour of anthophyllite. Phys Chem Miner 38:321–334
  28. Zema M, Oberti R, Boiocchi M, Tarantino S (2009) Thermal expansion and dehydrogenation processes in kaersutites: I—effects on unit-cell parameters. Epitome 3:248
• 作者单位：1. Dipartimento di Scienze della Terra e dell鈥橝mbiente, Universit脿 di Pavia, via Ferrata 1, 27100 Pavia, Italy2. CNR-Istituto di Geoscienze e Georisorse, Unit脿 di Pavia, via Ferrata 1, 27100 Pavia, Italy3. Department of Mineralogy, The Natural History Museum, Cromwell Road, London, SW7 5BD UK
• 刊物类别：Earth and Environmental Science
• 刊物主题：Earth sciences
  Geology
  Mineral Resources
  Mineralogy
  
• 出版者：Springer Berlin / Heidelberg
• ISSN：1432-0967

文摘

The thermoelastic behaviour of a natural gedrite having the crystal-chemical formula ANa_0.47 B(Na_0.03 Mg_1.05 Fe_0.862+ Mn_0.02 Ca_0.04) C(Mg_3.44 Fe_0.362+ Al_1.15 Ti_0.054+) T(Si_6.31 Al_1.69)O₂₂ W(OH)₂ has been studied by single-crystal X-ray diffraction to 973 K (Stage 1). After data collection at 973 K, the crystal was heated to 1,173 K to induce dehydrogenation, which was registered by significant changes in unit-cell parameters, M1–O3 and M3–O3 bond lengths and refined site-scattering values of M1 and M4 sites. These changes and the crystal-chemical formula calculated from structure refinement show that all Fe2+ originally at M4 migrates into the ribbon of octahedrally coordinated sites, where most of it oxidises to Fe3+, and there is a corresponding exchange of Mg from the ribbon into M4. The resulting composition is that of an oxo-gedrite with an inferred crystal-chemical formula ANa_0.47 B(Na_0.03 Mg_1.93 Ca_0.04) C(Mg_2.56 Mn_0.022+ Fe_0.102+ Fe_1.223+ Al_1.15 Ti_0.054+) T(Si_6.31 Al_1.69) O₂₂ W[O_1.122− (OH)_0.88]. This marked redistribution of Mg and Fe is interpreted as being driven by rapid dehydrogenation at the H3A and H3B sites, such that all available Fe in the structure orders at M1 and M3 sites and is oxidised to Fe3+. Thermoelastic data are reported for gedrite and oxo-gedrite; the latter was measured during cooling from 1,173 to 298 K (Stage 2) and checked after further heating to 1,273 K (Stage 3). The thermoelastic properties of gedrite and oxo-gedrite are compared with each other and those of anthophyllite.