High-pressure structural evolution and equation of state of analbite

Abstract

The volume and unit-cell parameters of analbite (i.e., NaAlSi3O8 with complete Al,Si disorder) have been determined by single-crystal X-ray diffraction to a maximum pressure of ~8.71 GPa. The volume variation with pressure is described by a fourth-order Birch-Murnaghan equation of state with K0T = 50.3(5) GPa, K0′ = 8.9(5), and K0″ = -2.4(3) GPa-1. The value of the room-pressure bulk modulus is ~4% lower than that of low albite, and the onset of volume softening in analbite is at ~6.7 GPa, some 1.7 GPa higher than the onset in albite. The anisotropy of compression of analbite is less than that in albite.