Compression of albite, NaAlSi3O8

Abstract

The structure and equation of state of low albite, NaAlSi3O8, has been determined using high-pressure single-crystal X-ray diffraction to a maximum pressure of 9.43 GPa. Low albite remains triclinic in space group C1̄ over the entire pressure range and no phase transitions were observed although the evolution of the unit-cell parameters and volume exhibit some unusual features at pressures above 4 GPa. A third-order Birch-Murnaghan equation of state fit to 6 P-V data points up to 3.4 GPa has K0 = 54.2(7) GPa and K’ = 5.3(6). At higher pressures the volume-pressure curve exhibits d2V/dP2 < 0 and the entire P-V data set can be approximated with a fourth-order Birch-Murnaghan equation of state with K0 = 52.3(9) GPa, K0’ = 8.8(6), and K0’’ = .2.8(2) GPa-1.