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 4th-order Birch Murnaghan Equation of State with K0T = 50.3(5) GPa, K’0 = 8.9(5) and K’’0 = - 2.4(3) GPa-1. The value of the room-pressure bulk modulus is ~ 1.9 % lower than that of low albite, and the on-set of volume softening in analbite is at ~ 6.7 GPa, some 1.7 GPa higher than the on-set in albite. The anisotropy of compression of analbite is less than that in albite. Single-crystal structure determinations of analbite to ~ 9.4 GPa show that there is no significant detectable compression of the T-O bonds within the structure, and the compression of the framework of tetrahedra is therefore accommodated by changes in the T-O-T angles which result in significant compression of the “crankshaft chains” within the framework. No significant shear of the tetrahedral rings of analbite was detected, in contrast to the structural compression of albite. Overall, the structural changes that occur in analbite from 0 to 9.4 GPa resemble those seen in ordered albite over the pressure range 0-4 GPa. Analbite shows a significantly greater structural rigidity than low albite over the larger pressure range. References. [1] Benusa, M.D., Angel, R.J., and Ross, N.L. (2005) American Mineralogist, 90, 1115-1120. [2] Downs, R.T., Hazen, R.M., and Finger, L.W. (1994) American Mineralogist, 79, 1042-1052. [3] Nestola F., Curetti N., Benna P., Ivaldi G., Angel R.J., and Bruno E. (2008) Canadian Mineralogist, 46, 1443-1454.
High-pressure structural evolution and equation of state of analbite.
CURETTI, Nadia;BENNA, Piera;
2010-01-01
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 4th-order Birch Murnaghan Equation of State with K0T = 50.3(5) GPa, K’0 = 8.9(5) and K’’0 = - 2.4(3) GPa-1. The value of the room-pressure bulk modulus is ~ 1.9 % lower than that of low albite, and the on-set of volume softening in analbite is at ~ 6.7 GPa, some 1.7 GPa higher than the on-set in albite. The anisotropy of compression of analbite is less than that in albite. Single-crystal structure determinations of analbite to ~ 9.4 GPa show that there is no significant detectable compression of the T-O bonds within the structure, and the compression of the framework of tetrahedra is therefore accommodated by changes in the T-O-T angles which result in significant compression of the “crankshaft chains” within the framework. No significant shear of the tetrahedral rings of analbite was detected, in contrast to the structural compression of albite. Overall, the structural changes that occur in analbite from 0 to 9.4 GPa resemble those seen in ordered albite over the pressure range 0-4 GPa. Analbite shows a significantly greater structural rigidity than low albite over the larger pressure range. References. [1] Benusa, M.D., Angel, R.J., and Ross, N.L. (2005) American Mineralogist, 90, 1115-1120. [2] Downs, R.T., Hazen, R.M., and Finger, L.W. (1994) American Mineralogist, 79, 1042-1052. [3] Nestola F., Curetti N., Benna P., Ivaldi G., Angel R.J., and Bruno E. (2008) Canadian Mineralogist, 46, 1443-1454.
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