title: Pressure induced elastic softening in framework aluminosilicate- albite (NaAlSi3O8).
abstract: Albite (NaAlSi3O8) is an aluminosilicate mineral. Its crystal structure consists of 3-D framework of Al and Si tetrahedral units. We have used Density Functional Theory to investigate the high-pressure behavior of the crystal structure and how it affects the elasticity of albite. Our results indicate elastic softening between 6-8 GPa. This is observed in all the individual elastic stiffness components. Our analysis indicates that the softening is due to the response of the three-dimensional tetrahedral framework, in particular by the pressure dependent changes in the tetrahedral tilts. At pressure <6 GPa, the PAW-GGA can be described by a Birch-Murnaghan equation of state with  = 687.4 Å3,  = 51.7 GPa, and  = 4.7. The shear modulus and its pressure derivative are  = 33.7 GPa, and  = 2.9. At 1 bar, the azimuthal compressional and shear wave anisotropy  = 42.8%, and  = 50.1%. We also investigate the densification of albite to a mixture of jadeite and quartz. The transformation is likely to cause a discontinuity in density, compressional, and shear wave velocity across the crust and mantle. This could partially account for the Mohorovicic discontinuity in thickened continental crustal regions.
authors.affiliation: Earth Materials Laboratory, Earth, Ocean and Atmospheric Sciences, Florida State University, Tallahassee, FL, 32310, USA.
authors.forename: Mainak
authors.initials: M
authors.lastname: Mookherjee
authors.affiliation: Géosciences Montpellier UMR CNRS 5243, Université Montpellier, 34095, Montpellier, France.
authors.forename: David
authors.initials: D
authors.lastname: Mainprice
authors.affiliation: Center for Simulation and Modeling, University of Pittsburgh, Pittsburgh, PA, 15260, USA.
authors.forename: Ketan
authors.initials: K
authors.lastname: Maheshwari
authors.affiliation: Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA.
authors.forename: Olle
authors.initials: O
authors.lastname: Heinonen
authors.affiliation: Earth Materials Laboratory, Earth, Ocean and Atmospheric Sciences, Florida State University, Tallahassee, FL, 32310, USA.
authors.forename: Dhenu
authors.initials: D
authors.lastname: Patel
authors.affiliation: Earth and Atmospheric Sciences, Cornell University, NY 14850, USA.
authors.forename: Anant
authors.initials: A
authors.lastname: Hariharan