Syntheses, volume, and structural changes of garnets in the pyrope- grossular join: implications for stability and mixing properties

J. Ganguly, Cheng Weiji Cheng, H. S.C. O'Neill

Research output: Contribution to journalArticle

79 Scopus citations

Abstract

Eleven garnet compositions in the pyrope-grossular join were synthesized from glass starting materials by a combination of hydrothermal synthesis and recycling of most of the products at ~40 kbar, 1400°C, in graphite capsules. The lattice parameters of the synthetic garnets have been determined with a precision of 0.0002-0.0004 Å. The results show a slightly positive excess volume of mixing, which is asymmetric toward the grossular end, and can be described by a subregular or Margules formulation with WV CaMg = 0.36 ± 0.23 and WV MgCa = 1.73 ± 0.3 cm3/mol (12 O atom basis). Powder X-ray diffraction (XRD) structural refinements show linear dependence of the O positional parameters and cation to O distance in dodecahedral, octahedral, and tetrahedral sites on the Ca content of garnet. The partial molar volume of grossular in pyrope-grossular and almandine-grossular joins varies smoothly and similarly between the terminal compositions and exceeds the molar volume by <1%. The partial molar volumes of pyrope and almandine change very similarly as a function of the Ca content of garnet. -from Authors

Original languageEnglish (US)
Pages (from-to)583-593
Number of pages11
JournalAmerican Mineralogist
Volume78
Issue number5-6
StatePublished - Jan 1 1993

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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