High temperature crystal chemistry of hydrous Mg- and Fe-rich cordierites

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dc.contributor.authorHochella, Michael F. Jr.en
dc.contributor.committeechairGibbs, Gerald V.en
dc.contributor.committeememberRibbe, Paul H.en
dc.contributor.committeememberRoss, F. K.en
dc.contributor.committeememberBloss, F. Donalden
dc.contributor.departmentGeological Sciencesen
dc.date.accessioned2014-03-14T21:41:28Zen
dc.date.adate2010-07-28en
dc.date.available2014-03-14T21:41:28Zen
dc.date.issued1977-07-05en
dc.date.rdate2010-07-28en
dc.date.sdate2010-07-28en
dc.description.abstractStructural refinements have been completed using data recorded for a Mg-rich cordierite at 24°C, 375°C, 775°C and 24°C (after heating to 775°C) and for an Fe-rich cordierite at 24°C and 375°C. The mean T-0 bond lengths in both cordierites remain unchanged but the mean octahedral bonds (M-0) lengthen upon heating. The unusually low thermal expansion of the Mg-cordierite is the result of its relatively "rigid" tetrahedral framework and the anisotropic expansion of octahedra isolated from each other. This anisotropic expansion leads to a slight rotation of the six-membered rings, a concomitant collapse of the structure parallel to c, and an expansion parallel to a and b. In the Fe-cordierite, the Fe-octahedron is more flattened, resulting in c being smaller and a and b being larger than the cell dimensions in the Mg-cordierite. Upon heating Fe-cordierite, there is no evidence for a rotation of the rings and a, b and c increase as the M-O bonds expand. A re-examination of the water orientation in the cavities of the Mg-cordierite using neutron and X-ray Δp maps confirms the orientation obtained previously by spectroscopic methods for type I water, i.e., H-O-H near (100) with the H-H vector nearly parallel to e. However, no evidence was found in the Δp maps for type II water. A peak ascribed to the alkali atoms that centers the six-membered ring becomes elongated parallel to a upon heating through 375°C, while the peak ascribed to the oxygen associated with H2O is absent in the Mg-cordierite at 775°C and in the Fe-cordierite at 375°C. After heating the Mg-cordierite to 775°C the peak reappeared in the Δp maps computed from data recorded at 24°C, but it no longer showed an elongation parallel to a as it did before heating.en
dc.description.degreeMaster of Scienceen
dc.format.extent110 leavesen
dc.format.mediumBTDen
dc.format.mimetypeapplication/pdfen
dc.identifier.otheretd-07282010-020312en
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-07282010-020312/en
dc.identifier.urihttp://hdl.handle.net/10919/43955en
dc.language.isoenen
dc.publisherVirginia Techen
dc.relation.haspartLD5655.V855_1977.H62.pdfen
dc.relation.isformatofOCLC# 06828424en
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjectanisotropic expansionen
dc.subject.lccLD5655.V855 1977.H62en
dc.titleHigh temperature crystal chemistry of hydrous Mg- and Fe-rich cordieritesen
dc.typeThesisen
dc.type.dcmitypeTexten
thesis.degree.disciplineGeological Sciencesen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.levelmastersen
thesis.degree.nameMaster of Scienceen

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