Original paper

Compressibility of clinochlore to 8 GPa at 298 K and a comparison with micas

Welch, Mark D.; Crichton, Wilson A.

Abstract

The equation of state of deuterated synthetic end-member C2/m clinochlore, Mg5Al(Si3Al)O10(OD)8, has been determined by synchrotron X-ray powder diffraction in the pressure range 0 - 7.7 GPa. The room-temperature bulk modulus K0 obtained from a fit of sixteen measurements to a second-order Birch-Murnaghan equation of state (K0' = 4) is K0 = 81.0 ± 0.5 GPa. Fitting to a third-order Birch-Murnaghan equation of state gives K0 = 83.1 ± 1.7 GPa and K0' = 3.3 ± 0.6 and, within error, the two fits are indistinguishable over this pressure range. Axial moduli (K0' = 4) for clinochlore are: K0a = 91(1) GPa, K0b = 89(1) GPa, K0c = 67(2) GPa. Comparison with published compressibilities for phlogopite, muscovite and phengite reveals that the micas are slightly less compressible along [100] and [010] than clinochlore, but micas are three times more compressible than clinochlore normal to the (001) structural layering. The very different compressibilities of micas and clinochlore normal to their polyhedral sheets indicates that the type of interlayer bonding has a major effect upon compressibility.

Keywords

synthetic clinochloremicascompressibilitybulk modulussynchrotron powder xrd