American Mineralogist · 1981 · 35 citations · 4 references
Crystal StructureEngineeringChemistryInorganic MaterialL0a PhaseCalcium AluminateMaterials ScienceInorganic ChemistryAtomic PhysicsPhysical ChemistryHydrogenSystem Mgo-sio 2Crystallography-H 2L2-coordinated Interlayer H2oMica FamilyPhysicochemical AnalysisPhase EquilibriumApplied PhysicsCondensed Matter Physics
The l0A phase is a unique pressure-dependent hydrous phyllosilicate in the system MgOSiOr-H2O which is stable at pressures between 32 and 95 kbar and temperatures up to 535'C. Although it was previously characterized as a 2rh-octahedral member of the mica family, reexamination of this phase has resulted in a new chemical and structural model represented by the formula [(H3O)2xrIMgyISilOrr(OH)r]. The results of X-ray powder difraction analysis, thermal analysis, and experiments in which the stoichiometry of oxide starting mixtures was carefully controlled indicate that the structure of the l0A phase is that of a fully trioctahedral 2:l phyllosilicate; it is similar to talc, but contains additional chemically-bound water in l2-coordinated sites [(HrO)]IIMg]ISi[O2.(OH[1.The results of infrared spectroscopy, however, indicate that this water is best represented as oxonium ions (H.O*) formed by interaction of the l2-coordinated interlayer H2O molecules with certain octahedral-layer hydroxyl groups accordiag to the relation:
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