Substitution of [6,4]Al in phlogopite: high-temperature solution calorimetry, heat capacities, and thermodynamic properties of the phlogopite-eastonite join

S. Circone, A. Navrotsky

Research output: Contribution to journalArticlepeer-review

37 Scopus citations

Abstract

Enthalpies of solution of synthetic magnesium aluminum phlogopite samples K(Mg3-xAlx)(Al1+xSi3-x)O10(OH)2 with 0.00 ≤ XEast ≤ 0.92 were measured in molten 2PbO-B2O3 at 977 K. The solid solution is destabilized more by [6]Mg,[4]Si substitution into eastonite than by [6]Al,[4]Al substitution into phlogopite, reflecting the increased strain in the mica structure at high [6,4]Al content that arises from increased lateral misfit between the smaller octahedral and larger tetrahedral sheets. The thermodynamic data for phlogopite and eastonite are assessed using the metastable reaction Phl + 3 Qtz = San + 3 En + H2O, in which the breakdown of magnesium aluminum phlogopite also produces spinel. A standard enthalpy of formation of phlogopite from the elements at 298 K of -6215.0 ± 3.5 kJ/mol is consistent with both data from high-temperature solution calorimetry and results from phase equilibria experiments. The standard enthalpy of formation of eastonite from the elements at 298 K is between -6352 and -6363 kJ/mol. -from Authors

Original languageEnglish (US)
Pages (from-to)1191-1205
Number of pages15
JournalAmerican Mineralogist
Volume77
Issue number11-12
StatePublished - 1992
Externally publishedYes

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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