Elasticity of tetragonal end-member majorite and solid solutions in the system Mg4Si4O12-Mg3Al2Si 3O12

S. V. Sinogeikin, J. D. Bass, B. O'Neill, T. Gasparik

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The adiabatic elastic moduli of polycrystalline En50Py50 and En80Py20 majorite-garnet solid solutions (where En=4MgSiO3, Py=Mg3Al2Si3O12) and the end-member En100 tetragonal majorite were determined at ambient conditions using Brillouin spectroscopy. The adiabatic bulk modulus, K, and shear modulus, μ, of En50Py50 were found to be K=173.1 (20) and μ=92.3 (10) GPa, and are indistinguishable from those of the end-member pyrope, Py100. The moduli of the more majorite-rich samples are significantly lower and are virtually identical to each other (K=162.6(11) and μ=85.7(7) for En80Py20; K=166(5) and μ=88(2) for En100). In combination with previously reported moduli for this system, we conclude that both K and μ are constant over the compositional range from Py100 to a majorite content of about 70-80%, whereupon the moduli decrease substantially. For compositions ranging from En80Py20 to the end-member majorite, the moduli are also approximately independent of composition, but at a lower value. An alternative model with a continuous decrease in moduli with increasing majorite content cannot be excluded, within the uncertainties of existing measurements. The contrast in moduli between aluminous pyrope garnet and Al-free majorite are small compared with the modulus changes accompanying the pyroxene - majorite phase transformation.

Original languageEnglish (US)
Pages (from-to)115-121
Number of pages7
JournalPhysics and Chemistry of Minerals
Issue number2
StatePublished - Feb 1997

ASJC Scopus subject areas

  • Materials Science(all)
  • Geochemistry and Petrology


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